Pigments: Historical, Chemical, and Artistic
Alizarin crimson ("Alizarin madder lake," "Alizarin"; also see Madder lake):
Origin and History: Madder lake was made from the European madder root, Rubia tinctorum. Since the 1850s (approximately) it has been made synthetically—under the name alizarin—with an identical chemical composition to madder but with a superior clear transparent tone and lightfastness. By manipulating these chemicals, a range of shades has been made from scarlet to ruby.
Making the Pigment: Roots of the madder plant are dried, crushed, hulled, boiled in weak acid to dissolve the dye, and fermented to hydrolyze anthraquinones from the glycosides. The extracted dye is made into a pigment by dissolving the dye in hot alum (aluminum potassium sulphate; AlK(SO4)2 × 12 H2O) solution, and precipitating pigment with soda or borax. Synthetic alizarin lakes are prepared by reaction of alizarine with aluminum hydroxide.
Chemical Properties: Stable di-arylide (PY 83). The base on which both varieties are substrated is indistinguishable under the microscope. Nor can the natural and artificial be identified even at high magnification. They are both soluble in hydrochloric acid.
Artistic Notes: All alizarin lake colors are permanent to light and to the gaseous atmospheres of urban areas. However, when mixed with ochre, sienna and umber, they lose their permanence, and when mixed with blacks or oxides, their permanence is not affected at all. Excellent as a glazing color over a dry surface. Alizarin madder lake is a coal-tar color, and in permanence exceeds the natural product, which in contrast ages more gracefully than the artificial.
Origin and History: Brazilwood dye comes from the Caesalpinia tree, and was named "brazil" even before the discovery of that country. In its natural state, brazilwood is a light, brownish red; mahogany in appearance. It is sold nowadays in blocks or chips, and sometimes in scrapings or shavings (as of 1960s). In the Middle Ages it was always sold in blocks, and the craftsman was obliged to reduce the solid wood to powder by scraping it with a piece of glass, or filing or pounding, as the finer the powder the more easily the color can be extracted from it.
Making the Pigment: When the brownish powder of brazilwood is wet it turns reddish. When steeped in a solution of lye it colors the liquid deep, purplish red, and hot solutions of alum extract the color from the wood in the form of an orange-red liquor. Most medieval brazil lakes were made either from the extract made with lye (a weak solution of potassium carbonate) or from the alum extract, as these solutions get the color out of the wood more thoroughly than plain water. Just what the shade is that is extracted depends on how acid or alkaline the mixture of solutions is made. The more alum: the warmer the color, the more lye: the colder the red. The precipitate is collected by settling and pouring off the liquid. The pasty mass is smeared on an absorbent surface such as a new brick or tile to dry. Then it is ground, and has the same degree of transparency as the alumina of which it is chiefly composed. When chalk is added to the alum, a more opaque pink rose is produced by the resulting admixture of calcium sulphate to the alumina lake. When white lead was used, it had no other effect than to give substance to the lake and slightly less transparency, rather than to make it opaque. When marble dust and powdered egg shells were added to newly formed lakes, they further controlled the color produced by reacting chemically with any excess of alum which might give a brown cast instead of rose. In all these cases the brazil color was mordanted upon the white material, so to speak, dyed with the brazil, and the pigment so formed was different from a mixture of a finished lake with a white pigment.
Artistic Notes: Brazil lakes are not very permanent.
Chemical Properties: Cadmium seleno-sulfide (PR 108).
Artistic Notes: Regarded as the best substitute for vermilion (which is mercury based as a sulphide of Mercury). As an oil color it needs a little wax and 40% oil. In tempera the color easily solidifies in the tube and is therefore better for the painter to prepare the color just before use. It is known to turn brown in outdoor frescos; with copper colors such as emerald green it turns black, as do all cadmiums. It should be noted that none of the reds the old masters used were as permanent as the cadmium range. In commercially available colors, it comes in light, medium and dark. Over-grinding can often make the paint gummy in feel, and quite dense, needing extra emulsions to attempt to bring it back to the feel of "paint". Cadmiums should never be mixed with lead white or other lead based paints, but can be mixed with the older Lithopone, Titanox and zinc oxides, and the more contemporary titanium whites.
Carmine ("Cochineal," "Crimson Lake"):
Origin and History: A dyestuff precipitated on clay, made from the ground female Coccus cacti, or cochineal, insect that lives on various cactus plants in Mexico and in Central and South America. It was brought to Europe shortly after the discovery of those countries, first described by Mathioli in 1549. The finest quality, known as nacarat carmine, is non-poisonous and quite beautiful with the peculiarity of being more permanent in transmitted light as a transparent color, than when under direct light.
Chemical Properties: Soluble in ammonia. Carmine is an aluminum and calcium salt of carminic acid, an anthraquinone derivative, and carmine lake is an aluminum or aluminum-tin lake of cochineal extract, whereas crimson lake is prepared by striking down an infusion of cochineal with a 5 per cent solution of alum and cream of tartar. Purple lake is prepared like carmine lake with the addition of lime to produce the deep purple tone. Carmine lake is insoluble in water. It burns completely leaving a white ash, and smells in the process like burnt horn.
Artistic Notes: According to Maximillian Toch, it is only legitimate as a food coloring, as exposure to the sunlight for three months bleaches the pigment completely. Carmine lake does not behave much better, being even weaker and less stable; it is of a maroon shade.
Origin and History: An important vegetable source or red is an East Indian shrub known as Pterocarpus draco, or Dradacoena draco. The sap of this shrub dries into a deep brownish-red gum resin which is known now as it was in the Middle Ages, as dragonsblood. The long, slender stems of the genus are flexible, and the older trees develop climbing propensities. The leaves have prickly stalks which often grow into long tails and the bark is provided with many hundreds of flattened spines. In classical times, dragonsblood was called Indian cinnabar by Greeks writers, but Pliny (whose word was law in the Middle Ages) professed that it was a product of a battle between the dragon and the elephant which ended in the mingling of the blood of each.
Making the Pigment: The berries are about the size of a cherry, and pointed. When ripe they are covered with a reddish, resinous substance which is separated in several ways, the most satisfactory being by steaming, or by shaking or rubbing in coarse, canvas bags. An inferior kind is obtained by boiling the fruits to obtain a decoction after they have undergone the second process.
Chemical Properties: Dragonsblood is not acted upon by water, but most of it is soluble in alcohol. It fuses by heat, and if heated gives off benzoic acid. It is astringent. The solution will stain marble a deep red, penetrating in proportion to the heat of the stone. It is very brittle, and breaks with an irregular, resinous fracture, is bright red and glossy inside, and darker red sometimes powdered with crimson, externally. Small, thin pieces are transparent. Various chemical analyses: 1) 50 to 70 per cent resinous compound of benzoic and benzoyl-acetic acid, with dracoresinotannol, and also dracon alban and dracoresene. (2) 56.8 per cent of red resin compounded of the first three mentioned above, 2.5 per cent of the white, amorphous dracoalban, 13.58 of the yellow, resinousdracoresene, 18.4 vegetable debris, and 8.3 per cent. ash. (3) 90.7 per cent of red resin, draconin, 2.0 of fixed oil, 3.0 of benzoic acid, 1.6 of calcium oxalate, and 3.7 of calcium phosphate. (4) 2.5 per cent of draco-alban, 13.58 of draco resen, 56.86 of draco resin, benzoic dracoresinotannol ester and benzoylaceticdracoresinotannol ester, with 18.4 of insoluble substances.
Artistic Notes: The main uses of this red resin in the Middle Ages were coloring metal, improving the color of gold, and for glazing other metals to imitate gold. It was used as a pigment chiefly by book painters. Though not a lake pigment, it resembles them in transparency.
Origin and History: The work "Lake" in pigments derives from a material known as Lacca from which they were prepared. We don't know what just was meant by lacca but have supposed that was the material we now call Lac, the gum lac of India, a dark-red encrustation of resin which is produced on certain kinds of trees by the sting of certain insects. This resin is the source of our shellac.
Making the Pigment: Crude lac, known as stick-lac, consists of the resin, the encrusted insects, lac dye, and twigs. When crushed and washed free of the dye, twigs, and insects, it becomes granular and is known as seed-lac or grained lac. If the crude material is boiled with water and a little alkali, the coloring matter dissolves in the water; it is dried into thin layers or flakes and sold (rarely now) as "lac dye".
Chemical Properties: Lac dye is pH sensitive and produces its red color in acidic mediums only; alkaline mediums produce a bluish color.
Artistic Notes: Lac dye is used for painting, or a lake can be colored with it. The one pigment still made with it is called Indian Lake. The colors that lac dye produces are generally violet, and not very brilliant. The color is too dark and dull for books, and not stable enough for walls.
Origin and History: The boiled root of Rubia tinctoria, a field plant which grows wild in Italy and was cultivated in France as a dyestuff in the end of the thirteenth century. As an extract of the root of the madder plant, which was allowed to grow for two years in the ground, the root is not red itself, but contains alizarine, which can be made to produce red lakes of several shades and precipitated on a clay base.
Artistic Notes: It is a beautiful transparent red, but impermanent. In the trade it is available as rose, light, medium to dark, and violet. Rose madder bleaches out in a few months, but the darker tones are more permanent. In fresco, lime destroys madder completely. In the original root there is a second coloring agent called purpurin, which when removed creates a superior permanence. Madder lake requires about 70% binder, dries poorly and should therefore be first mixed with linseed oil and ground with an addition of varnish (damar). It has been observed over time that madder lake bleeds, and when so it has been an indication that it has not been used properly, perhaps too thickly in underpainting, or that it has been mixed with impermanent coal-tar dyes.
Minium ("Saturn red," "red lead"):
Chemical Properties: Red oxide of lead, not to be confused with iron oxide. It is highly poisonous, sensitive to hydrogen sulphide, attacked by hydrochloric acid but indifferent to alkalis. Red lead also should not discolor alcohol; if it does it has been adulterated with coal-tar dye (most likely a test of the color upon purchase from the chemists at that time); also, when doctored with coal-tar it has a tendency to bleed when painted over with white lead. Dilute nitric acid turns red lead into brown lead peroxide: the last stage to which white lead may be oxidized. Under great heat red lead becomes a light violet, and when cooled again, a yellowish red.
Making the Pigment: It is produced by heating white lead in the presence of air.
Artistic Notes: As a pigment, it quickly turns dark in the light, but when mixed with oil (and it requires only 15% binder), it is fairly permanent. When mixed in oil with white lead, it tends to fade rather than turn dark, and stands up better than white lead with vermilion. It can only be used as an oil color; as a powder and in fresco it eventually turns black. Freshly ground is best, and when red lead is produced under insufficient heat, red-yellow oxide forms, which is not sufficiently permanent. This can be eliminated by washing with sugar-water. When it is ground in oil, a little wax should be added to guard against its hardening too quickly. Red lead ground in oil dries the quickest of all pigments.
Origin and History: Realgar was not as common as orpiment in medieval paintings, with references limited largely to preservation of glair, and only sometimes used as a pigment.
Chemical Properties: The first cousin of orpiment, both being an arsenic disulphide; realgar is an orange-scarlet to orpiment's yellow. Arsenic tri-sulfide is sometimes made, if you can find it.
Artistic Notes: This is a color rarely available today, but the best crystals look clear and transparent.
Sinopia ("Sinoper, "Sinope"):
Origin and History: The name of a shade of red ocher that eventually was used to describe any red ocher, of which there are many variations in color: a light and warn tone is Venetian Red, or Mars Red; darker, more cool-toned purple versions are called Indian Red, Mars Violet or Caput Mortuum; Terra Rosa from Pozzuoli has a salmon pink color which is easily recognizable in some medieval Italian wall paintings, whereas the dark wine red of ground hematite is more common on the wall paintings of Florence. The red iron oxides are artificial pigments made from iron ore or the waste material of chemical industries, though they are closely related to the red earths and have very similar properties.
Artistic Notes: Red iron oxides, if ground too finely in oil, have a tendency to bleed, whereas versions of sinopia will not. English red, which is a light red, is often cut with gypsum when in the powder form, making it dangerous to use in fresco. All of these pigments need 40-60% binder, possess good covering power, and dry fairly well. When mixed with whites, they yield cool tones, and can be used for all purposes in all techniques. Sinopias work well for underpainting.
Origin and History: Vermilion is the standard name given to the red pigment based on artificially-made mercuric sulfide. The common red crystalline form of mercuric sulfide is cinnabar, a name reserved only for the natural mineral. The natural product found chiefly in Almaden and Idria has been eliminated for practical purposes (including that it is slightly poisonous).
Making the Pigment: The synthesis of these mercury and sulphur into cinnabar is accomplished by mixing them together and heating them; if simply mixed and ground together, a black sulfide of mercury is formed, but at the proper temperature this vaporizes and recondenses in the top of the flask in which it is heated. The flask is then broken and the vermilion is removed and ground. Upon grinding the red color begins to appear, and the longer it is ground, the finer the color becomes. This process was understood before the year 800 AD.
Chemical Properties: The properties of both natural and artificially prepared are practically identical. Cinnabar, a dense red mineral, is the principal ore of mercury or quicksilver. Vermilion is not generally considered today to be a permanent pigment. It has been known since Roman times that specimens of vermilion darken when exposed to light. In tests it has been discovered that impurities in the alkali polysylfides used to "digest" the pigment, leading to the instability of the red. This catalyzes the transition of the red to black. Also, we've found that the darkening of vermilion occurs mainly in paintings in egg tempera but it is not unknown in oil paintings. It is however fairly unreactive to other colors' chemical makeups; therefore, when mixed with lead white to produce flesh tones, it did not produce the black sulfides.
Artistic Notes: The traditional use of red glazes of madder, kermes, and cochineal lakes over vermilion underpaint not only increases the purity of the color but has been shown to reduce the tendency to darken as well. It is also known that the farther light can penetrate into the binding medium, the more quickly the vermilion will darken. To give vermilion an agreeable luster in manuscript decoration, the use of egg yolk along with the glair was how the color was normally tempered in books.
Barium yellow ("Permanent yellow," "yellow ultramarine"):
Chemical Properties: Barium chromate. When heated it becomes reddish, and returns to yellow when cooled.
Artistic Notes: It appears to be similar to zinc yellow, but somewhat brighter, and is luminously bright under artificial light, almost white. It is also slightly poisonous, and superior to zinc yellow in its permanence, and its requirement for binder being only 30% and thus leaner. It is fairly permanent in tempera, watercolor and pastel, but doubtful in fresco, though even then better than zinc yellow.
Cadmium yellow ("Aurora yellow"):
Origin and History: The cadmium yellows are bright and opaque, permanent and non- poisonous, first introduced to the public at the 1851 Exhibition, and said to have been made first in 1846.
Making the Pigment: A solution of 9,7 g Cd(NO3)2 × 4 H2O in 50 ml deionized water is added slowly to a stirred solution of 8,3 g Na2S × 9 H2O in 50 ml deionized water. The resulting precipitate is filtered, dried and homogenized in a mortar.
Chemical Properties: Cadmium zinc sulfide (PY 35) = Cadmium Yellow Lemon; cadmium sulfide (PT 37) = Cadmium Yellow Light, Medium. They are also permanent in lyes, but behaves oddly when heated: if heated to red it returns to yellow, but turns to orange within a year. In the open, they turn brown when mixed with lime. Cadmium lemon is precipitated upon a white filler.
Artistic Notes: Some commercial samples turn green under light, but others stand up well. The darker cadmiums have more covering power and are more permanent. Cadmium is not compatible with copper colors such as emerald green, as in mixtures with them turns them permanently black. Many cadmiums in powder form show streaks under light; the cause being cadmium salts other than sulphide.
Gamboge ("rattan yellow," "wisteria yellow"):
Origin and History: The earliest evidence of the use of gamboge comes from eighth century East Asia. After its arrival in Europe in the seventeenth century, gamboge was used as a transparent oil color by Flemish painters, but additives such as resin or wax were necessary to enhance its permanence and durability. The pigment was also made more usable by mixing it with other yellow pigments such as lemon yellow or alumnia. Many sources refer to gamboge being used to make a transparent yellow varnish for the coloring of wood, metals, and leather.
Making the Pigment: Gamboge is most commonly extracted by tapping from the tree Garcinia hanburyi. The trees must be ten years old before they are tapped. The resin is extracted by making spiral incisions in the bark and by breaking off the leaves and shoots of the tree and letting the milky yellow resinous gum drip out. The resulting latex that exudes out is collected in hollow bamboo. When the latex is congealed, the bamboo is broken away and large rods of raw gamboge remain. Raw gamboge is usually in the form of hard, brittle lumps of a dull, dark yellow color, which when pulverized, turns into a bright yellow powder. This powder is ground or mixed with a variety of binders in order to make paints and varnishes.
Chemical Properties: It burns with an odor of resin, is poisonous, is not attacked by acids, and turns red in alkalis. Gamboge usually contains about 70% to 80% yellow resin, and 15% to 25% water-soluble gum. the remaining portion is composed of esters, hydrocarbons, wax, ash residue, and vegetable detritus. Most investigation of commercial gamboge products have found that the major constituent of the resin is gambogic acid. R1=(CH2)2C=CH(CH2)2,R 2=CO2H,R3=CH3 There has been less investigation of the gum component of the pigment, but it is hydrocarbon based.
Artistic Notes: A transparent dark mustard yellow gum resin pigment much used in watercolor, which is neither lightproof alone or when mixed with other pigments. In thick layers it shows a gloss because of its resin content, and as an oil color it strikes through, therefore being unusable. When mixed with most high-chroma pigments, the gamboge eventually disappears and what was once a beautiful green or orange turns back into blue or red. Economically, other pigments are more sensible to use, so the use of gamboge has drastically declined in the twentieth century. In fact, modern-day pigment experts recommend that the only admissible use for gamboge is in leaf-gilding on paper or parchment by pre-coating the support, then breathing on the paper to make it tacky.
Gold leaf and shell gold:
Origin and History: The most important yellow color of the Middle Ages, the light reflecting from gold leaf was the source of the term "illuminated" manuscript.
Making the Pigment: Gold leaf is composed of 22k or 23k gold, pounded to a thickness of only a few m (micrometers). Shell gold is made from powdered gold held together with a binder such as gum arabic; it is called "shell" gold because the pigment is commonly stored in a shell. You can make your own shell gold from gold leaf scraps.
Origin and History: All of the paintings that have been identified as containing lead-tin yellow date between approximately 1300 and 1750. This hue was used most frequently in the 15th, 16th, and 17th centuries. One of the most important uses of lead-tin yellow pigment was in the color glass production in Venice and Bologna in the Middle Ages. It was used widely in Western Europe in frescoes and panels.
Chemical Properties: Lead-tin oxide, or lead stannate, Pb2SnO4. Massicot pigment decomposes very slowly even when boiling with very concentrated acids. This pigment can be used in lime medium because it is not affected by alkalis. Soluble sulfides cause darkening of the pigment with formation of lead sulfide.
Artistic notes: Commonly used in foliage with green and earth pigments.
Massicot ("Cassel Yellow," "Litharge"):
Origin and History: May also have been called "giallorino" in the Middle Ages. Massicot is a very old pigment that can be dated back to as early as 1300 in Medieval Europe.
Chemical Properties: White monoxide of lead, PbO. Heated slowly, it forms a warm yellow. It is the heaviest of the lead pigments, slightly orange in color, and forms a cement which is impervious to water when mixed with linseed oil. To form an actual cement, it is mixed with glycerine. It makes a drier known as lead drier when cooked at over 500 degrees F and mixed with linseed (this is the lowest temperature in which it becomes soluble).
Naples yellow ("Lead antimonate yellow"):
Origin and History: It was used as early as 500 BC, replenished 79 AD in the Vesuvius eruption, and said to have been found on the tiles of Babylon.
Making the Pigment: Twelve oz. of ceruse, 2 oz. of the sulphuret of antimony, 1/2 oz. of calcined alum, 1 oz. of sal ammoniac. Pulverize these ingredients, and having mixed them thoroughly, put them into a capsule or crucible of earth, and place over it a covering of the same substance. Expose it at first to a gentle heat, which must be gradually increased till the capsule is moderately red. The oxidation arising from this process requires, at least, 5 hours' exposure to heat before it is completed. The result of this calcination is Naples yellow, which is ground in water on a porphyry slab with an ivory spatula, as iron alters the color. The paste is then dried and preserved for use. There is no necessity of adhering so strictly to the doses as to prevent their being varied. If a golden color be required in the yellow, the proportions of the sulphuret of antimony and muriate of ammonia must be increased. In like manner, if you wish it to be more fusible, increase the quantities of sulphuret of antimony and calcined sulphate of alumina.
Chemical Properties: Opaque lead antimoniate. Identical crystal-structure with the mineral, bindheimite.
Artistic Notes: It is very heavy and dense, and therefore of exceptional covering power; moreover, as a lead color it is a good dryer, but poisonous as all leads are. Manufacturers distinguish between Naples yellow and dark Naples yellow; both are very permanent. In oil, tempera and even fresco, excellent use can be made of Naples yellow as it is compatible with all other colors. It is a much more compact compound of lead than lead white, requiring only 15% binder, and it is totally unaffected by light. It seldom cracks, and in varnished tempera is invaluable because of its covering power. Discoloration has been proven in tempera colors from the tube, where the metal of the tube was attacked by disinfectants contained in the tempera medium, which creates a dirty gray. Naples yellow needs little grinding; only a brief working with the spatula, and if too finely ground becomes heavier and earthy in texture, therefore best when made by hand, and not previously manufactured.
Orpiment ("King's Yellow"):
Origin and History: Orpiment is a stone, found throughout the world as a low-temperature product of hydrothermal veins, hot-spring deposits, and volcanic sublimation. In its natural state, it has a mica-like sparkle that recalls the luster of metallic gold. An ancient pigment, used throughout the Middle East and Asia through the late 19th century. During the Renaissance, orpiment was imported to Venice from Asia Minor.
Making the Pigment: Mineral orpiment is heated with sulfur, allowing a more pure orpiment to sublime out. Orpiment is particularly difficult to grind into a pigment. An artificial variety of pigment is made by fusing of arsenic or arsenic oxide with sulfur.
Chemical Properties: Yellow Arsenic Tri-sulfide, As2S3. Monoclinic, transparent to opaque. In close proximity, orpiment can react with lead colors such as flake white and minium ("red lead," an orange color). It outgases, meaning that orpiment vapors will creep over to the lead colors and corrupt them, reverting them to a lead-gray color. This process can creep a couple of inches in as many months, or less. It cannot be used to modify green tones containing verdigris, as the sulphur of the orpiment attacks copper in the same way. It also has a corrosive action on binding materials, and has quite often decayed and come away from panels and parchment. Orpiment is highly toxic.
Artistic Notes: Its color is light, vivid yellow in color, sometimes pure yellow but often inclined toward orange. When mixed with zinc or titanium white, it loses its yellow tones becoming a pale brown/beige.
Making the Pigment: Colored earth is mined, ground and washed, leaving a mixture of minerals—essentially rust-stained clay. Ochre can be used raw (yellowish), or roasted for a deeper (brown-red) color from loss of water of hydration.
Chemical Properties: One of many earth-tones created by natural iron hydoxide (PY 43). When heated, it turns red, losing its chemically bound water content to become thick and dense. Under moderate heat, yellowish-red colors are produced; however, the stronger the heat, the more rich and saturated the color produced, which if mixed with white create colder tones than one would expect. The coloring agent is of an iron oxide. To heat, the ochres have to be pure and free from adulterant admixtures such as chalk, because this would create quick-lime if heated. Artistic Notes: Gypsum should also never be present especially if intended for fresco use. They are opaque and non-poisonous, but require a high percentage of binder. Produces a quick-drying oil paint.
Chromium oxide green ("chrome green"):
Origin and History: First made in 1809, this is a permanent, opaque, and less toxic alternative to emerald green.
Chemical Properties: Anhydrous chromium senquioxide (PG 17), Cr2O3. The relatively weak ligand field of the chromium-oxygen bonding at the chromiums produces color in a similar manner to that of the emerald green below.
Origin and History: This pigment of mineral origin was known to the Egyptians, the Greeks and the Romans. Chrysocolla was a classical name to indicate various compounds that were useful in the hard soldering of gold, and among these were certain green copper minerals, the basic carbonate, the silicate, etc. The name is now used by mineralogists, specifically, for natural copper silicate (approx. CuSiO3.nH2O), a mineral fairly common in secondary copper ore deposits. Often chrysocolla is found together with malachite and azurite in the same deposit. In its natural state, chrysocolla appears similar to malachite, except that the color is somewhat more bluish. Microscopically, it is nearly amorphous or cryptocrystalline, and is practically colorless or, at most, only a pale green by transmitted light.
Chemical Properties: CuSiO3 * nH2O + Cu2CO3(OH)2 + CuCO3(OH)2 monoclinic aggregate, idiochromatic copper. Copper silicate.
Artistic Notes: Chrysocolla is stable to light and fairly opaque. When ground to a powder it retains its green color quite satisfactorily and may serve for a pigment in an aqueous medium. Since the copper is bound in a silicate matrix, it is not as soluble when in an acidic medium. Therefore chrysocolla, unlike azurite and malachite may be used in oil. It can be used for fresco and tempera. It is not suitable for encaustic. It had mostly fall into disuse by the early 17th century, possibly clinging on longest as a watercolor pigment.
Emerald green ("Paris green," "Veronese green," "Schweinfurt green"):
Origin and History: Emerald green was developed in 1808 in an attempt to improve Scheele's green. It was first produced commercially by the firm of Wilhelm Sattler at Schweinfurt, Germany in 1814.
Making the Pigment: Justus Von Liebig and Andre Bracconot separately published papers on its method of manufacture. Verdigris (or acetic acid) was dissolved in vinegar and warmed. A watery solution of white arsenic was added to it so that a dirty green solution was formed. To correct the color, fresh vinegar was added to dissolve the solid particles. The solution was then boiled and bright blue-green sediment was obtained. It was then separated from the liquid, washed and dried on low heat and ground in thirty- percent linseed oil.
Chemical Properties: A basic copper aceto-arsonite, Cu3(AsO4)2 * 4H2O Highly poisonous; it will blacken any adjacent sulphur color (ie: vermilion, French ultramarine, cadmium yellow). Emerald turns black when heated and smells of garlic. Potassium hydroxide discolors emerald to an ochre color, and in weak sulfuric acid it dissolves, turning the solution blue. The copper colors of the old masters look under the microscope like coarse glass splinters as compared with modern colors which have a mud-like character.
Artistic Notes: It can be used for tempera and oil. Not advised for fresco and encaustic. The color is luminous by itself, bluish or yellowish green, highly permanent and would be very useful except that it is incompatible with sulphur colors such as cadmium yellow, vermilion and ultramarine. As an oil color, emerald green requires only small amounts of oil: no more than 30%, and dries well.
Malachite ("mountain green," "Bremen green," " Olympian green," "copper green," "green bice"):
Origin and History: Malachite is found in many parts of the world in the upper oxidized zones of copper ore deposits, associated in nature with azurite, the native blue carbonate of copper, which contains less chemically bound water. Geologically, azurite is the parent, and malachite a changed form of the original blue deposit. Malachite was first used in Egypt and China. In fact, Egyptians probably used the pigment as eye paint even before the first Egyptian dynasty. In Western China, malachite is found in many paintings from the ninth and tenth centuries. Europeans did not use malachite very much in medieval times, but it was very popular during the Renaissance. However, it had been replaced by synthetic green pigments by about 1800.
Making the Pigment: The natural mineral is crushed, ground to a chalk-like powder, then washed and levigated—swirled in water to separate the finer particles. The powder becomes paler the more it is ground. In the lab, 12,5 g CuSO4 × 5 H2O are solved in 50 ml deionized water. A solution of 5,8 g Na2CO3 in 55 ml deionized water is added slowly to the vigorously stirred solution of copper(II) sulfate. After adding of approximately 40 ml solution strong reaction sets in and carbon dioxide is being developed. The remaining solution should be added slowly after the onset of the reaction. The reaction mixture is let to stand for one to two days at temperatures between 5 and 10°C in order to obtain finely crystallized precipitate. The suspension is decanted two times with deionized water, filtered off and washed thoroughly.
Chemical Properties: A secondary mineral ore of copper carbonate, CuCO3.Cu(OH)2. When it is slowly heated, finely crushed malachite gives off water and carbon dioxide (CO2), finally becoming black cupric oxide (CuO). In acid solution, it dissolves and releases carbon dioxide, but remains green. In reaction with hot sodium hydroxide (NaOH), cupric oxide forms on the surface, but the pigment does not react with cold sodium hydroxide. Finely powdered malachite is also slowly darkened by hydrogen sulfide (H2S).
Artistic Notes: To be useful as a bright green it must be ground coarse, as finely ground renders it too pale. It is moderately permanent and unaffected by strong light. When used as a paint, malachite's shade also changes with the medium used. As a watercolor, it is a pale green, but it becomes darker in oil. It works better in egg tempera than in oil.
Phthalocyanine green ("phthalo green," "monastral green"):
Origin and History: A bright blue-green developed in 1935 and in use since 1938.
Chemical Properties: Chlorinated copper phthalocyanine (PG 7), or copper with one of its atoms removed to make a non-metallic pigment.
Artistic Notes: Phthalo green has a very high tinting strength and transparency. Many painters have been warned away from it because of this color strength. This pigment doesn't react to sulfur as metallic copper does; it's transparent and covers from yellow-green to cyan.
Origin and History: The berries of buckthorn, in the genus Rhamnus, were gathered when they were ripe, yielding the color now known as sap green. When gathered before ripening, they yielded a yellow color; the compound of their unripe juice with alum was not much used, but was recorded in the sixteenth century under the name berry yellow. The fourteenth century method was to use the verjuice alone in its natural state to enrich mixed greens. Rhamnus berries are still sold, dried, under the name of graines d'Avignon, or Persian berries.
Artistic Notes: Not permanent or lightfast.
Terre verte ("green earth"):
Origin and History: The name terre verte is applied to several different minerals, but most importantly in medieval painting is the light, cold green of celadonite, found chiefly in small deposits in rock in the area of Verona, Italy. The chief deposits of glauconite that yield the yellowish and olive sorts are in Czechoslovakia. Today the color is chiefly a durable mixture of chromium oxide, black, white and ochre, since the natural product is scarcely obtainable, though possible with effort.
Chemical Properties: They are not poisonous, dissolve partially with a yellowish-green color in hydrochloric acid, but not in alkalis, and should not discolor water, alcohol or ammonia.
Artistic Notes: Can be rather dull, transparent, and soapy in texture, like a clay. The color is also not constant, ranging from a light bluish gray with a greenish cast to a dark, brownish olive. In manuscripts and on panels they were chiefly used to underpaint the warm flesh tones.
Verdigris ("green of Greece," "salt green"):
Making the Pigment: Made by treating copper sheets with the vapors of vinegar, wine, or urine and scraping the resultant corroded crust. Placing copper in ammonia will cause it to turn blue; adding a few drops of acetic acid (vinegar) precipitates a light cyan-green salt. Copper sheets can also be spread with honey and sprinkled with salt before treated with the acid for a slightly different shade termed "salt green."
Chemical Properties: Copper acetates ranging in color from green to blue. Reactions with copper acetate vary among substances such as the following: copper acetates dissolve in mineral acid, alkalis convert them into blue copper hydroxide, oils, resins and proteins react to form green transparent copper oleates, resinates, and proteinates. Of the many different types of verdigris each type can be classified into either basic or acidic. Neutral verdigris is Cu(CH3COO)2× H2O, and basic verdigris contains more Cu(OH)2 and H2O. Neutral verdigris is neutral copper acetate that occurs when basic acetates are dissolved in acetic acid, or when basic verdigris is ground up with strong acidic acid. Decomposition of neutral verdigris occurs when a solution is boiled. This verdigris is dissolved in acidic acid. The shape of neutral verdigris is hexagonal and rhombic with distinct boundaries. Basic verdigris forms from the combination of air, water vapor, acetic acid vapor, and copper or copper alloy mix. It forms a solid of blue, or blue-green. It is often made up of fine needles. In the presence of HCl, verdigris is soluble and forms a green solution. From interaction with NaOH it is soluble and precipitates. In the first three months of use the verdigris formulations can change from blue-green to green. All verdigris reacts with resin to form copper resinates. This copper resinate is rather transparent and often used as an overpaint to increase depth of saturation of an opaque green.
Artistic Notes: Verdigris is reactive and unstable, requiring painters to use isolating varnishes to protect its color. Sulfur compounds in the air darken all forms of verdigris. It is, however, lightfast.
Viridian ("Guignet's green," "Permanent Green"):
Origin and History: Guignet of Paris patented the process for manufacturing viridian or transparent oxide of chromium in 1859. Viridian is a non-poisonous, permanent color that replaced verdigris and emerald green as a glazing color by the turn of the 20th century.
Making the Pigment: Mix 3 parts of boracic acid and 1 part of bichromate of potassa, heat to about redness. Oxygen gas and water are given off. The resulting salt when thrown into water is decomposed. The precipitate is collected and washed.
Chemical Properties: Hydrated chromium sesquioxide (PG 18). Its tint is muted like colors of the natural world. Interestingly, viridian becomes very permanent when roasted into chromium oxide green. Viridian is distinguished microscopically by its large particle size. Viridian's particles are slightly rounded and the pigment is insoluble and unchanged in chemical tests.
Artistic Notes: Although viridian requires much more binder to grind it as an oil paint (50-100%) compared to thirty percent in chromium oxide green, both are good driers. Viridian, however, is prone to cracking if one uses this transparent pigment too thickly.
Azurite ("Blue verditer," "mountain blue," "lapis armenius," "azurium citramarinum," "blue bice"):
Origin and History: Latin borrowed a Persian word for blue, lajoard, which in the form of lazurium became azurium, and gave us our word azure. It is composed of a basic carbonate of copper, found in many parts of the world in the upper oxidized portions of copper ore deposits. Azurite mineral is usually associated in nature with malachite, the green basic carbonate of copper that is far more abundant. Azurite was the most important blue pigment in European painting throughout the middle ages and Renaissance by contrast, despite the more exotic and costly ultramarine having received greater acclaim.
Making the Pigment: To prepare a color from it, lump azurite is ground into a powder, and sieved. Coarsely ground azurite produces dark blue, and fine grinding produces a lighter tone; however if not ground fine enough, it is too sandy and gritty to be used as a pigment. The medieval system included washing it to remove any mud and then separating the different grains by some process of levigation. If plain water is used it is a slow, laborious process, so they used solutions of soap, gum and lye. When azurite is washed, the very fine particles are rather pale, greenish sky-blue, and not much admired for painting. The best grades of azurite for painting were coarse: not sandy, but so coarse that it could be quite laborious to lay them on.
Chemical Properties: Cu3[CO3]2[0H]2, H3.5, SG-3.7, monoclinic. Azurite sometimes looks a little like lapis lazuli, and the two were often confused in the Middle Ages. To tell them apart with certainty the stones were heated red-hot. Azurite turns black when this is done, and true lapis is not injured. It does not blacken from the effects of sulphur gases as some chemists have supposed, but from the action of the strong alkalis improperly used in picture cleaning, and from the purely optical effect of darkened varnish surrounding its particles. The color can, however, be ruined by the presence of acids.
Artistic Notes: Glue size was often used as a binder to hold the pigment grains firmly in place. (Size is more easily affected by protracted dampness or by washing than egg tempera, and blues in wall paintings have therefore sometimes perished through the destruction of their binder where colors in tempera have stood.) It was necessary to apply several coats of azurite to produce a solid blue, but the result was quite beautiful. The actual thickness of the crust of blue added to the richness of the effect, and each tiny grain of the powdered crystalline mineral sparkled like a minute sapphire, especially before it was varnished. The open texture of a coat of azurite blue has often been its undoing on panels; the varnish sinks into it and surrounds the particles of blue. As the varnish yellows and darkens, the power of the azurite to reflect blue light is destroyed, strangled by the varnish--a large number of blacks in medieval paintings were originally blues, only obscured by the discoloration of the varnish. It is incredibly permanent.
Origin and History: Although Höpfner introduced cerulean blue as early as 1821, it was not widely available until its reintroduction in 1860 by George Rowney in England. Its name was derived from the Latin word caeruleum, meaning sky or heavens. Cerulean was used in classical times to describe various blue pigments. This is a greenish, light, very pure and dense compound of cobaltous and tin oxides (is supposed to be a stannate of cobalt). You can get a similar blue by mixing and firing tin and copper chalcanthite with quartz sand like the Egyptians did to make their highly prized frit colors.
Making the Pigment: Cerulean is cobaltous stannate and is made by mixing cobaltous chloride with potassium stannate. The mixture is thoroughly washed, mixed with silica and calcium sulfate and heated.
Artistic Notes: As a color, it is very valuable to the landscape artist in atmospheric tones, though this color can also be made by using greenish Prussian blue with zinc oxide. It is absolutely permanent (though in the tube it needs an addition of 2% wax). This variety is a fairly true blue (not greenish or purplish) but it does not have the opacity or richness of cobalt blue. It is not recommended for use in watercolor painting because of chalkiness in washes. In oil, it keeps its color better than any other blue.
Cobalt blue ("Azure"):
Origin and History: A modern replacement for smalt, cobalt blue is a non-poisonous metal color. The isolation of the blue color of smalt was discovered in the first half of the eighteenth century by the Swedish chemist Brandt. In 1777, Gahn and Wenzel found cobalt aluminate during research on cobalt compounds, but the color was not manufactured commercially until late in 1803 or 1804.
Making the Pigment: 1 g Cobalt(II)-chloride (CoCl2 × 6H2O) and 5 g Aluminum chloride are homogenized in a mortar and heated in a test tube with a gas burner for about 3 to 4 minutes.
Chemical Properties: Cobalt oxide and aluminum oxide (PB 28); black cobalt oxide fires blue. It is unaffected by acids, alkalis and heat. It has coarse particles, like azurite and ultramarine, genuine but is distinguished microscopically by their non-crystalline appearance. It is chemically insoluble and unchanged, even in strong hydrochloric acid.
Artistic Notes: Cobalt blue is useful in all techniques, as well as being lightproof. It needs 100% binder but dries very quickly in oil, with the same drying power as the metal lead. Because of this, it often causes cracks in the picture when painted over layers which are not sufficiently dry. Cobalt blue is susceptible to the yellowing of oils, as all cool tones do, but yields a clear tone whereas ultramarine in thick layers, if not mixed with sufficient white, appears to be black. It is totally stable in watercolor and fresco techniques.
Egyptian blue ("frit," "Pompeiian blue"):
Origin and History: Very stable synthetical pigment of varying blue colour. It is one of the oldest man-made colors commonly found on wall paintings in Egypt, Mesopotamia and Rome. Many specimens, well over 3000 years old, appear to be little changed by the time.
Making the Pigment: Heating a mixture of a calcium compound (carbonate, sulfate or hydroxide), copper compound (oxide or malachite) and quartz or silica gel in proportions that correspond to a ratio of 4 SiO2 : 1 CaO : 1 CuO to a temperature of 900°C using a flux of sodium carbonate, potassium carbonate or borax. The mixture is then maintained at a temperature of 800°C for a period ranging from 10 to 100 hours.
Chemical Properties: Calcium copper silicate, CaCuSi4O10. It is insoluble in acids even in warm temperatures.
Artistic Notes: It has a discreet covering power. It can be used in fresco. Not advised in tempera, oil and encaustic.
French ultramarine ("French blue," Guimet's blue," "permanent blue," "synthetic ultramarine"):
Origin and History: Ultramarine is imitated nowadays by a process that was invented in France in the eighteenth century as a result of a prize offered by the French government. The raw materials of ultramarine manufacture are soda and china clay and coal and sulphur, all common and inexpensive materials. The process requires skill, is inexpensive, and the product is many thousand times less costly than genuine ultramarine prepared from lapis lazuli. The first observance of the substance was made by Goethe in 1787, when he noticed blue deposits on the walls of lime kilns near Palermo. He mentioned that the glassy blue masses were cut and used locally as a substitute for lapis in decorative work. In 1928, Jean Baptiste Guimet perfected a method of producing an artificial, and cheaper, ultramarine pigment.
Making the Pigment: Artificial ultramarine, also known as French ultramarine was made by heating, in a closed-fire clay furnace, a finely ground mixture of China clay, soda ash, coal or wood, charcoal, silica and sulfur. The mixture was maintained at red heat for one hour and then allowed to cool. It was then washed to remove excess sodium sulfate, dried and ground until the proper degree of fineness was obtained.
Chemical Properties: Because the particles in synthetic ultramarine are smaller and more uniform than natural ultramarine, they diffuse light more evenly. Chemically, the artificial ultramarines are not distinguishable from the blue particles of genuine lapis; you can only tell by the percentage of colorless optically active crystals, whereas the artificial is pure blue and free from diluting elements.
Artistic Notes: Synthetic ultramarine is not as vivid a blue as natural ultramarine. Synthetic ultramarine is also not as permanent as natural ultramarine. French ultramarine is light-resisting, but owing to the use of sulphur in its manufacture, may discolor in the presence of acid.
Indigo (also see Woad):
Origin and History: Indigo was probably used as a painting pigment by ancient Greeks and Romans. Marco Polo (13th century) was the first to report on the preparation of indigo in India. The Indiagofera tinctoria thrives in a tropical climate; the active ingredient is found in the leaves, an indol derivative is fermented from a sugar. Aniline blue has the same chemical composition and replaced it in 1870.
Making the Pigment: To prepare the dye, freshly cut plants are soaked until soft, packed into vats and left to ferment. It is then pressed into cakes for use as a watercolor or dried and ground into a fine powder for use as an oil paint. In the lab, 4 g o-nitrobenzaldehyde is dissolved in 40 ml acetone using a 200 ml erlenmeyer flask. 20 ml deionized water are then added and the flask is shaken thoroughly. Next, 16 ml of a 1 molar solution of sodium hydroxide is added slowly. The mixture is stirred with a glass rod and left standing for five minutes. The precipitated indigo is then filtered off and dried at room temperature.
Chemical Properties: C16H10 N2O2. Some of the various chemical tests by which indigo may be identified are: sublimation test, nitric acid test, hydrosulfite test, solubility tests, and thin-layer chromatography. Indigo is characterized as having a good lightfastness (light resistance), good to moderate alcohol resistance, and low oil resistance. Indigo's chemical properties make it difficult to dissolve in hot ethanol, amyl alcohol, acetone, ethyl acetate, and pinene, but readily soluble in boiling aniline, nitrobenzene, naphthalene, phenol and phthalic anhydride. It is heat resistant to 150 degrees Celsius and is resistant to air. This precipitation is insoluble in water. Alkalis dissolve it and form the sodium salt indigo white, which oxidizes into many shades of blue. A by-product of this natural plant dye formed a pigment which is heavy and impermanent, therefore cumbersome to use, along with Thioindigo, a red-violet coal tar pigment which is permanent, though only in watercolor.
Artistic Notes: Indigo does not hold up in an oil base. It has fair tinting strength and may fade rapidly when exposed to strong sunlight. Worked in tempera or beneath varnish it can be very stable. It is also stable when exposed to hydrogen sulfide.
Lapis lazuli ("Genuine ultramarine," "azzurrum ultramarine", "azzurrum transmarinum", "azzuro oltramarino", "azur d'Acre", "pierre d'azur", "Lazurstein"):
Origin and History: Made from the semi-precious stone lapis lazuli. A rock of many compounds: lazurite, a sodium sulfosilicate ore, deep blue crystals. Hauyne, sodalite (a sodium aluminum silicate with sodium chloride that occurs in crystals and masses), and nosean. Lapis lazuli is a contact metamorphic mineral found in limestone and granite; the best is found in Afghanistan, from ancient times until today. The earliest occurrence of use as a pigment was in the sixth and seventh century wall paintings in cave temples at Bamiyan in Afghanistan. When it was used in medieval Italy, its most extensive use was in illuminated manuscripts and panel paintings, complementing the use of vermilion and gold, and was as expensive as gold to work in. The highest quality and most intensely blue-colored ultramarine was often reserved for the robes of Christ and the Virgin. Graduations of color were easily achieved and quite beautiful, but the cost eventually drove it into obsolescence.
Making the Pigment: As it is such a hard stone, it is difficult to separate the pigment from the other constituents. The blue cannot be separated from the impurities by washing with water, as noted in Byzantine texts, as doing so would create a gray powder. Natural ultramarine is purified from ground lapis lazuli by mixing it with wax and kneading in a dilute lye bath. The brilliant blue lazurite crystals preferentially wash out and are collected.
Chemical Properties: A complex sulfur-containing sodium aluminum silicate, Na8-10Al6Si6O24S2-4. Chemically, the mineral lapis lazuli from which the pigment is made is an extremely hard and complex rock mixture: a mineralized limestone containing grains of the blue cubic mineral called lazurite, which is the essential constituent of the pigment. Also present, however, are two isomorphous minerals, one containing sulphate and the other, chloride, both of which sometimes occur in a blue form, as well as other colors. There are other silicates which may also be present, creating variables in the quality and appearance of the stone. The best are of a uniform deep blue, but can be paler as there is a great deal of white calcite and iron pyrites in it that sparkle like gold; there is also the possible intermingling with white crystalline materials.
Artistic Notes: Natural ultramarine has a high stability to light as is proven by the fact that examples on paintings as much as five hundred years old have as intense and pure a blue color as either the freshly extracted pigment or the best synthetic. There is a disorder known as "ultramarine sickness" which has occasionally been noted on paintings as a grayish or yellowish gray mottled discoloration of the paint surface which also occurs from time to time with artificial ultramarine used industrially, which is brought about by the action of atmospheric sulphur dioxide and moisture. An alternative cause may be the acidity of an oil or oleo-resinous paint medium: the slow drying of the oil during which time water may have been absorbed to cause swelling, opacity of the medium and therefore whitening of the paint film. A difference in color tone and value was achieved by glazing with other colors, such as ochre and white, particularly in skies, over the ultramarine. This was made necessary by the cost of the pigment, which would be largely lost in mixtures.
Phthalocyanine blue ("Monastral blue," "heliogen blue," "phthalo blue," "copper phthalocyanine"):
Origin and History: An organic blue dyestuff that was developed by chemists under the trade name, "monastral blue," and presented as a pigment in London, November 1935.
Making the Pigment: It is prepared by fusing together phthalic anhydride and urea to copper chloride, first washing it in dilute caustic soda and then in dilute hydrochloric acid. It then becomes copper phthalocyanine, but is not conditioned as a pigment until it is dissolved in concentrated sulfuric acid and carefully washed in excess water and filtered, the resulting paste being used thus directly in the preparation of lakes by adsorption on aluminum hydrate, or dried for incorporation into non-aqueous mediums.
Chemical Properties: It is a highly complex organic synthesis. Pure copper phthalocyanine in crystalline form is a deep blue with a strong bronze reflection, but when dry in pigment form is bright blue without any bronziness. They' re lightfast, and an ideal pure blue for it absorbs light almost completely except for the green and blue bands. When photographed, this line of colors tends to turn brown in the camera lens, being logically attributed to the fact that though it absorbs all other colors of light, there must be some refractive or reflective bounce of the initial bronze tone of the mineral in crystal that is not evident to the eye.
Artistic Notes: Phthalo green has a very high tinting strength and transparency. Many painters have been warned away from it because of this color strength. It doesn't react to sulfur as metallic copper does. The pigment is extremely fine and light in its powdered form; a drop of denatured alcohol helps it go into solution with a binder.
Prussian blue ("Paris blue"):
Origin and History: The pure pigment, called the first of the modern pigments, is Paris blue and has a coppery reddish sheen. Its invention at the beginning of the eighteenth century displaced azurite from the European palette. It was made by the colormaker Diesbach of Berlin in about 1704. Diesbach accidentally formed the blue pigment when experimenting with the oxidation of iron. The pigment was available to artists by 1724 and was extremely popular throughout the three centuries since its discovery.
Making the Pigment: Dissolve sulphate of iron (copperas, green vitriol) in water; boil the solution. Add nitric acid until red fumes cease to come off, and enough sulphuric acid to render the liquor clear. This is the persulphate of iron. To this add a solution of ferrocyanide of potassium (yellow prussiate of potash), as long as any precipitate is produced. Wash this precipitate thoroughly with water acidulated with sulphuric acid, and dry in a warm place.
Chemical Properties: It is a compound of iron and cyanogen, ferri-ammonium ferrocyanide (PB 27:1). Antwerp blue and Milori blue are adulterated products which, because of their intense chromatic power, are often met with. Paris blue is instantly discolored by potassium hydroxide, and is sensitive to all alkalis.
Artistic Notes: Paris blue is non-poisonous, uncommonly strong in coloring power and very permanent in all techniques except fresco, where it loses intensity and leaves rust colored spots. It can also in very light mixtures be known to bleach out. Paris blue dries well but takes up 80% binder. Paris blue in paintings is splendid when used with oxide of chromium brilliant or in shadows when mixed with madder lake; being sparing in its use, because as an oil color, it tends to give the picture a darker, heavier character than cobalt blue or ultramarine. It can be used in tempera and watercolors, where when mixed with zinc white, it has the peculiar characteristic of fading when exposed to light, but completely regaining its chromatic strength in the dark.
Smalt ("starch blue"):
Origin and History: First described by Borghini in 1584. A moderately fine to coarsely ground potassium glass of blue color, due to the small but variable amounts of cobalt added as cobalt oxide during manufacture. The principal source of cobalt used in this preparation in Europe during the Middle Ages appearing to be the mineral smaltite, one of the skutterudite mineral series. In the seventeenth and eighteenth centuries other associated cobalt minerals were probably used as well (erythrite and cobaltite). Cobalt ores were also used for coloring glass in Egyptian and classical times. The origin or cobalt tinted glass probably coincided with the development of vitreous enamel techniques; near east in origin, as enamels were made from easily fusible powdered and colored materials similar to glass.
Making the Pigment: The cobalt ore was roasted and the cobalt oxide obtained was melted together with quartz and potash or added to molten glass. When poured into cold water, the blue melt disintegrated into particles, and there were ground in water mills and elutriated. Several grades of smalt were made according to cobalt content and grain size. In the complex ores in Saxony, as they were first roasted, much of the arsenic was volatilized. The oxides of cobalt, nickel and iron were then melted together with siliceous sand, and the resulting product called Zaffre or Zaffera were, in part, sold to potters and glassmakers. The rest of the product was used instead of potash. A violet tint was obtained.
Artistic Notes: As smalt is a glass, its particles are transparent, and its hiding power is lower, even than that of cobalt blue. Therefore it must be coarsely ground for use as a pigment. When used in oil medium, it has a tendency to settle and streak down perpendicular surfaces. Like all glass-based pigments, it is stable unless improperly made, and is better in aqueous media and lime for fresco.
Turnsole ("folium," "heliotrope"):
Origin and History: An organic pigment made from the plant now called Crozophora tinctoria. The turnsole violet was highly esteemed in fourteenth century Italy, as a common and universal shading for all colors. The clothlets were the most convenient form of colors for illuminators, as it was placed in a dish, wetted with a little glair or gum water, and the color would dissolve out of the cloth and into the medium, forming a transparent stain.
Making the Pigment: The dye was called turnsole when blue, and folium when red, the variation being a result of pH sensitivity. Extraction of the color from the seeds was done by saturating bits of cloth with the juice of the seed of capsules, which were gathered in the summer. The juice was extracted by squeezing gently so that the kernels were not broken; when a good supply was collected the cloths were dipped into it, dried, and re-dipped and re-dried over and over until they had soaked up substantial color. For red, plain linen cloth would work, for violet, they were first soaked in lime-water and dried so the lime would neutralize the acidity; for blue the cloths were used to soak up the color and then exposed to ammonia to increase the alkaline content. As a blue it was impermanent and would revert to violet, but this was not considered a flaw, and large quantities of turnsole were used in the later Middle Ages.
Woad (also see Indigo):
Origin and History: A substitute for the imported Indian indigo (even in classic times) was known in the native European weed called in Latin, Glastum or Isatic, and in English, woad: a shrubby herb with broad, green leaves which contain the raw material of a blue dyestuff. Both indigo and woad were a very dark, purplish, even blackish color, and less attractive than when it is mixed with a material to lighten it. Color was also sometimes made with a lime made from eggshells. A whole family of indigo or woad pigments consisting of mixtures of indigo with powdered marble, natural and calcined, calcined gypsum, calcined eggshells and white lead we now regard as pigments in themselves, independent of the indigo from which they were made. However, considering the extra cost of indigo, naturally it was largely replaced in the Middle Ages by domestic indigo from woad. Woad was grown commercially in England until the early 1950s as an adjunct to dyeing with true indigo. It's known as a "gross feeder" that exhausts the land it's grown on unless the salts it extracts are constantly replaced.
Making the Pigment: Simply gathering the leaves produces a deep and lasting blue-black stain on the hands. Woad leaves were stripped from the plants, crushed, made up into balls forming the common raw material of commerce in domestic indigo; for use in dyeing they were powdered, spread out, damped and allowed to ferment. They were then made up into a dye bath with water and bran (other materials were used as well) and subjected to further fermentation, all of which took great skill. In the course of dyeing, a scum collects on he surface of the vat. Called "Florey" or the flower of the woad, this was skimmed off, dried and used alone or in elaborate compounds under the name of indigo in the Middle Ages.
Chemical Properties: Chemically, there is little difference between this blue and that of indigo.
Origin and History: A purplish-brown iron oxide color. Adding heat [calcine] brings out the red side of iron oxide and adds a transparent quality if silicates are involved, as in sienna. Magnesium is also present in caput mortuum.
Origin and History: The remarkable range of pigments that could be produced with cobalt included cobalt violet, known since 1859. Salvetat first described the preparation of cobalt violet, dark in Comptes Rendus des Seances de l'Academie des Sciences XLVIII in an article titled, "Matieres minerales colorantes vertes et violettes." The light variety was developed in Germany in the early nineteenth century and is anhydrous cobalt arsenate.
Making the Pigment: The dark variety is anhydrous cobalt phosphate which was made by mixing soluble cobalt salt with disodium phosphate. It is washed and then heated at a high temperature. The light variety is particularly poisonous because of its arsenic content. 2 g of cobalt chloride and 1,3 g of sodium hydrogenphosphate are each solved in 20 ml deionized water, the solutions are poured together and the resulting precipitate is filtered off.
Chemical Properties: Co3(PO4)2 or Co3(AsO4)2. This French product is a cobaltous oxide arsenate, and therefore extremely poisonous. Dark cobalt violet, a cobaltous phosphate, is a German product and is very permanent as opposed to the French variety, but is quite expensive, and thus hardly necessary. Cobalt violets appear as irregular-shaped particles and particle clusters under the microscope and are largely unaffected by chemical tests.
Artistic Notes: In tempera it is not a good tube color as it hardens too easily, and the commercial watercolors of this pigment also have an extremely short tube life. The light variety of cobalt violet turns dark in oil due to the yellowing of linseed oil. Both of the cobalt violets are considered to be very permanent. They are both compatible with all painting media. Their transparency, weak tinting strength and high cost limited their use but their fastness to light made them more desirable than the older organic dye violets.
Origin and History: This is a Nuremberg violet, a mineral violet and is permanent, heat-proof and non-poisonous. However, as a manufactured product, it is not a beautiful tone, tinting use occasionally in fresco and mineral painting. The new manganese violets of German manufacture are powerful, fast colors furnished in several tones. This pigment was invented by Leykhuf in 1868.
Chemical Properties: Manganese ammonium phosphate (PV 16), (NH4)2Mn2(P2O7)2 - Mn3(PO4)2 * 3H2O. When heated it fuses into a hard white substance. It is a pyrophosphate mananoso ammoniac and a manganese phosphate with phosphoric acid, by making the purple mass boil with carbonate ammonium. It is filtered, washed and finally fused.
Artistic Notes: It covers and dries well in oil and tempera, and works well in pastel, encaustic and watercolor, but not in fresco. It has a discreet opacity.
Tyrian purple ("Royal purple"):
Origin and History: This organic dye was prepared from various mollusks or whelks, including Murex brandaris, Purpura haemostoma, Purpura lapillus, and Carpillus purpura, which can be found on the shores of the Mediterranean and Atlantic coasts and which excrete the fluid from which the dye is won. One gram of this dye is made from the secretion of 10,000 of these large sea snails.
Chemical Properties: This purple color is remarkably stable, resisting alkalis, soap, and most acids. It is insoluble in most organic solvents.
Artistic Notes: Tyrian purple was used in the preparation of a purple ink and in dyeing parchments upon which the codices of Byzantium were written. It was also the traditional "Imperial Purple" of ancient emperors, kings, and magistrates.
Origin and History: A French brown pigment of organic, vegetal and synthetic origin, which as used as a chalk or an ink. In Britain, and especially France from where the name derives, the color is in fact produced from beechwood, the root of which is mixed with gum Arabic and water. In the seventeenth century, it was used primarily as a wash, as can be seen in Rembrandt's drawings, which were mostly done in this technique. Questionable, however, is whether bistre's source was done with or without the presence of air in the process.
Chemical Properties: It is a compound not clearly identified in chemistry.
Artistic Notes: Its major use is the watercolor medium because its color is similar to asphaltum that is used in oil medium, although it can be used in oils if required. It is soluble in turpentine and naphtha and it is also used in the oil technique. Not advised for fresco, encaustic and tempera.
Bitumen ("Asphaltum," "Judaic Bitumen," "Antwerp Brown"):
Origin and History: A pigment of mineral organic and natural origin and is a mixture of hydrocarbons, waxes and petroleum. It is sometimes classified as dark brown. Found in Egypt, Trinidad, Perù, this blackish reddish color, which can vary dependant on source, became of more importance in oil painting techniques, in which it is often responsible for a characteristic cracking or 'alligatoring' of the surface. Very popular in sixteenth and seventeenth to provide fleshtone shadows.
Making the Pigment: It is produced from the slow oxidation and slow polymerization of petrol and similar organic materials.
Chemical Properties: CnH2n + 2. It is soluble in turpentine, naphtha and organic solvents while it is insoluble in water and alcohol.
Artistic Notes: It has a discreet opacity but is sometimes difficult to dry. Not advised in the tempera technique, fresco and encaustic.
Making the Pigment: Like bone black, it is made by charring bones, but the brown is an incomplete process, and therefore contains tarry matter which is non-drying and retards the drying of all other pigments it is mixed with. This matter also makes the pigment fugitive to light, further reducing the value of it in traditional methods.
Making the Pigment: Burnt sienna is prepared by calcining raw sienna which in the process undergoes a great change in hue and depth of color; in going from ferric hydrate of raw earth to ferric oxide, it turns to a warm, reddish brown.
Chemical Properties: Fe2O3 * nH2O + Al2O3 (60%) Manganese dioxide (1%), calcined natural iron oxide (PBr 7). Microscopically, heating makes the pigment more even in color and the grains are reddish brown by transmitted light.
Artistic Notes: Because of its transparency, burnt sienna is used as a fiery glazing color which requires much binder, about 180%, and as an oil color is apt to jelly. This is remedied by washing, which however dilutes the intensity of the color. In 1768, Martin Knoller stated that very strong heat will produce a sienna resembling vermilion that may be used in fresco out of doors. American Burnt Sienna is a strong type of ochre and is neither as clear nor as brilliant as the Italian Sienna. It supposedly imparts a muddy tone but is very permanent in all techniques.
Making the Pigment: Burnt umber is a combination of iron oxide, oxide of manganese and clay, made by burning raw umber to drive off the liquid content.
Chemical Properties: An ochre containing manganese oxide and iron hydroxide (PBr 7), Fe2O3 × MnO2. In acids it dissolves in part leaving a yellow solution; hydrochloric acid gives it an odor of chlorine. In alkalis it discolors a little and when heated, becomes a reddish brown. It has the same properties as natural umber.
Artistic Notes: Completely lightfast and unaffected by gases, and makes a good glaze when thinned with oil or varnish. Because of the manganese content it is an excellent dryer. It can be used in all techniques but requires 80% binder, with an additional 2% wax when in tubes to prevent hardening. Many umbers have a greenish tinge, and in oil, it tends to turn dark later on, especially if the underlayers were not thoroughly dried, but this darkening may also occur in alla prima painting. It is best not to use the color in fresco, as in the open it tends to decompose and produces a burnt heavy tone. Can be mixed with all other pigments except for the Lakes. Burnt umber turns especially dark, surprisingly as the burnt tones are usually more reliable in this respect. This tendency to darken is increased by the modern practice of grinding the tube colors too finely.
Vandyke brown ("Cassel brown", "cologne earth," "Caste Earth"):
Origin and History: Made from humic substances in soil, peat or brown coal, this color is found in the pictures of the old masters, among them Rubens, who used it mixed with gold ochre as a warm, transparent brown, which held up particularly well in resin varnish.
Artistic Notes: It is partially soluble in oil and has a slight tendency to turn gray (most apparent when used in whites). When used with resin ethereal varnish it is more permanent than when used in oil; however, this is impossible in painting, and unnecessary. It requires 70% binder. For restoring purposes it is useful when mixed with varnish. It is sensitive to lyes and becomes a cold gray in fresco, making it useless on a wall. This color is fugitive to light and unreliable.
Origin and History: Made from bones which have not been entirely charred, and treasured by painters for their warm tones.
Artistic Notes: This is the least permanent of all the black colors, requires 100% binder as all blacks do, and doesn't always dry well.
Origin and History: Prepared by charring bones, horns etc., in the absence of air. Ivory black was established in antiquity by the example of Apelles, but there is no evidence that it was continued in the Middle Ages.
Chemical Properties: It is partially soluble in acids.
Artistic notes: It is the purest and deepest black. It is the best dryer, and can be used in all techniques. When used by itself over a smooth white ground of for example, lead or cremnitz white, it cracks, but not when slightly mixed with other colors.
Making the Pigment: Lampblack is made by allowing a flame to play on a cold surface and collecting the soot which the flame deposited. Sometimes a beeswax candle, sometimes tallow; sometimes the flame of a lamp burning linseed, hempseed or olive oil; or by burning pitch or incense. It makes a difference as to what the source of the flame is as the black itself is pure carbon, but there are apt to be unburnt particles which may affect the color and working properties of the pigment. You can make your own lampblack ink using this method.
Artistic Notes: Lampblack is often used for ink-making as it has an extremely fine grain and doesn't need grinding; it only needs to be mixed with a little gum water to make what we call India ink. Lampblack pigment is absolutely permanent; we know that pure carbon black will never fade, but the material with which the ink was bound has often perished or become brittle, and the surface of parchment is so hard and close grained that even the fine grains of lampblack may fail to penetrate it if the lampblack is suspended in a strong solution of gum. When mixed with water or water media, it becomes so light that the powder floats and is not very manageable; a drop or two of denatured alcohol helps it go into solution. It tends to be a bit greasy; and though an excellent pure black, apt to muddy a bit in mixtures.
Origin and History: Charcoal made from young shoots of grape vines were referred to in medieval times as the best of blacks. It is now referred to as more of a blue-black, considering the coolness of the grays that it produces in mixtures.
Making the Pigment: It is important that the vine sprigs be thoroughly burnt and reduced to carbon, otherwise the color will be brownish and an unpleasant consistency; but they must not be burnt in the air or they might reduce to ashes instead of to carbon. They are packed tightly in little bundles in casseroles, covered and sealed, and baked in a slow oven. You can make your own vine black with a similar method. The resulting charcoal is used in sticks for drawing; for painting it is first powdered and ground up dry, and then mixed with water and ground for a long time between two hard stones.
Cremnitz white (Also see Lead white.):
Origin and History: Some companies offer the color Cremnitz white, but this is a misnomer because the original pigment for Cremnitz white has not been made since 1938.
Chemical Properties: The same as lead or flake white, but made by a slightly different chemical process which leaves a faint vinegar odor.
Artistic Notes: Not very permanent to sulphur gases, and therefore other whites are far better to use.
Lead white ("flake white," "kerms white," "Berlin white," "silver white," "slate white"):
Origin and History: Used since antiquity, lead white was the only white used in European easel paintings until the 19th century. Lead white strongly absorbs X-rays, thus can be detected in paintings easily. It is one of the oldest man-made pigments, and its history dates back to the Ancient Greeks and Egyptians.
Making the Pigment: It is a by-product of lead, and the purity of the color depends on the purity of the lead. Purifying processes greatly increase the cost of the product. White lead has always been one of the most important pigments in many painting techniques; yet chemists are still undecided as to just what our normal modern lead white is. The traditional method is called "the stack process." The "stack" consists of hundreds or thousands of earthenware pots containing vinegar and lead, embedded in fermenting tanbark or dung. They are shaped in a way that the vinegar and lead are separate, but the lead is still exposed to the vapors of the vinegar, by being coiled into a spiral which stands on a ledge inside the pot, above the well of vinegar in the bottom. It is then loosely covered with a grid of lead, which keeps the tan from falling in, allowing the carbon dioxide formed by the fermenting of the tan to enter the pot and act upon the coils and plates of lead with the vapors of vinegar and moisture. A thick layer of tan is spread out on the ground: the bottom of the pit, and the pots with lead and vinegar are arranged upon it, covered with their leaden grids. More tan is laid over them and then usually a loose flooring of boards, followed by more pots, more tan, and so on until all the pots are imbedded. Old tan partly used up, in certain proportions, will continue to maintain proper heat. The heat, moisture, acetic acid vapor and carbon dioxide do their work for a month or so, and the stacks are dismantled. The metallic lead by this point has been largely converted into a crust of white lead on the coils and grid. These are then separated from the unconverted metal and washed free of acid and soluble salts, and ground for future use in painting.
Chemical Properties: Lead is a poison that builds up an incurable case of lead poisoning by breathing in a little of the dust of white lead, day after day, over time. Once it gets into the human system, it stays there until the body's tolerance level is met, and then becomes symptomatic. Medieval writers warn against the dangers of apoplexy, epilepsy, and paralysis, which come with exposure to it. Lead white darkens in the presence of sulphur, so should not be used in conjunction with cadmium colors or French ultramarine.
Artistic Notes: Lead white has the warmest masstone of all the whites. It has a very subtle reddish-yellow undertone that is almost unnoticeable unless you are looking for it, or comparing lead white side by side with other kinds of white. This undertone is minimal in the best quality of lead whites. You will notice that lead white has a heavier consistency than other whites. This is because the pigment is particularly dense and does not lend itself to a paint of soft consistency. Lead white is also the fastest drying of all of the whites because of the drying action of the lead pigment upon the oil. This makes lead white particularly valuable for painters who need a relatively fast drying time for underpainting or alla Prima techniques.
Origin and History: A titanium pigment, manufactured by F. Weber Co. of Philadelphia in 1921. Was at one time the best known white pigment used by artists. Today it is not nearly so well-known. Artistic Notes: It was 78% pigment with 22% oil, which must have prevented it from yellowing. Its hiding power was greater than that of flake white, and had no chemical reactions to other pigments. It was completely permanent and worked in all techniques.
Origin and History: Titanium White is truly the white of the 20th century. Although the pigment titanium dioxide was discovered in 1821, it was not until 1916 that modern technology had progressed to the point where it could be mass produced. First made commercially in Norway for industrial purposes. There are many industrial grades of titanium white pigment, none of which are used in their pure form for artists oil color. In oil, it dries to a spongy film that is quite unsuitable for artistic purposes. For this reason, titanium dioxide is always blended with one or more of the other white pigments, or an inert pigment to make a suitable artists oil color. Since titanium dioxide, by itself, dries to a spongy film and zinc oxide dries to a brittle film, the two are combined in a balanced blend for better quality, professional grade titanium whites. In some brands, where zinc oxide predominates in the mixture, the color is called titanium-zinc white. Cheaper brands of budget grade paint are known to use a mixture of titanium dioxide with Barytes or other inert pigments. Use of these types of whites is really a false economy because they lack both the brilliance and tinting strength of professional grade color.
Chemical Properties: Titanium dioxide, TiO2.
Artistic Notes: A non-poisonous, good covering paint that is useful in all techniques. The masstone of titanium white is neither warm nor cool and lies somewhere between lead white and zinc white, in that respect. It has a tinting strength superior to either of the other whites, and a drying time that is slower than that of lead white but faster than that of zinc white. It is truly an all-purpose white oil color. There is certain dispute about its drying abilities, but does remain even in mixtures. It yellows easily, especially in tube paints that have been mixed with heavy oil. Avoid any tubes of titanium that have oil residue at the top of the tube when opening, as these will surely yellow, and within a very short time. Titaniums are sometimes cut with large quantities of zinc white to improve their drying time and cohesion with the oil.
Zinc white ("Chinese white," "silver white"):
Origin and History: First introduced in 1840, this white is colder in appearance than lead white, and doesn't cover nearly as well, yet it is far less expensive. Zinc has been known as a mineral since antiquity when it was melted with copper to form brass. It was also known then, as it is today, as a medicinal ointment. In 1782, zinc oxide was suggested as a white pigment. Guyton de Morveau at L'Académie de Dijon, France, reported zinc oxide as a substitute for white lead. Metallic zinc had originally come from China and the East Indies. When zinc ore was found in Europe, large-scale production of the extracted metallic zinc began. In 1834, Winsor and Newton, Limited, of London, introduced a particularly dense form of zinc oxide which was sold as Chinese white. It was different from former zinc white in that the zinc was heated at much higher temperatures than the late eighteenth century variety. By 1844, a better zinc white for oil was developed by LeClaire in Paris. He ground the zinc oxide with poppy oil that had been made fast drying by boiling it with pyrolusite (MnO2). In 1845, he was producing the oil paint on a large scale.
Making the Pigment: The French method of manufacturing, known as the 'indirect process' used the zinc smoke derived from molten zinc, which was heated to 150°C and collected in a series of chambers.
Chemical Properties: Zinc oxide, ZnO. If you heat zinc white, it turns to lemon yellow, but will revert to white when cooled. It differs from lead white in this respect. Since zinc oxide is derived from smoke fumes, its particles are very fine and are difficult to observe except at very high magnification. It readily dissolves in alkaline solutions, acids and ammonia without foaming.
Artistic Notes: It is non-poisonous, permanent and doesn't yellow, though these factors are true only with pure zinc white. It also disintegrates quickly out of doors, and increases in volume causing massive crackling, so it is not useful in fresco. Ground in oil it dries slowly, especially in poppy oil, where the retarded drying time is needed. It does not dry as solid as lead white, due to some transparency in the pigment. A small addition of damar or mastic varnish speeds up the drying time. As it is very fine in powder form, it can be sufficiently mixed with only a spatula, requiring 30% binder and an addition of 2% wax in the tube to prevent hardening. It is compatible with all other pigments, including copper-based, but in watercolor it is destructive to the permanency of coal-tar colors and accelerates the process of fading (though it doesn't do this in oil.) Zinc is essentially permanent in sunlight although the yellowing in oil affects its brightness. It is neither as opaque nor heavy as lead white and it takes much longer to dry. Because zinc white is so "clean" it is very valuable for making tints with other colors. Tints made with zinc white show every nuance of a color's undertones to a degree greater than tints made with other whites, and the artist has time to complete his work before the paint dries. Despite its many advantages over lead white, zinc white oil color also has a drawback; it makes a rather brittle dry paint film when used unmixed with other colors. Zinc whites' lack of pliancy can cause cracks in paintings after only a few years if this color is used straight up to excess.