Pigments
Alizarin Crimson
Madder lake was made from the European madder root, Rubia tinctorum.
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.
Vine Black:
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.
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.
Lead white("flake white," "kerms white," "Berlin white," "silver white," "slate white") :
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.
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.
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, that 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.
Carmine("Cochineal," "Crimson Lake"):
A dyestuff precipitated on clay, made from the ground female Coccus cacti, or cochineal, insect which 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.
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.
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.
Vermilion("Cinnabar"):
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).
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.
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.
Burnt Sienna:
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.
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.
The inhabitants of the principal Phoenician cities of Byblos, Sidon and Tyre were granted Roman citizenship. These cities were centers of the pottery, glass and purple dye industries.
Because of the Phoenicians' unique purple potion, one possible meaning for the word Phoenician is "dealer in purple!" Others think it means "blood-red" because their purple dye had a reddish undertone.
Another name for this superb color was "Tyrian purple" because Tyre was a famous Phoenician city located on the eastern shore of the Mediterranean. Everyone called Tyre the "queen of the seas" because it was the center of the Phoenicians' trade empire. Soon they realized that they needed a simpler writing system for their bookkeeping because so many people wanted the dye and their business exploded. They didn't have the patience to write in artistic hieroglyphics, so they invented a simple alphabet in the twelfth century B.C. Tyre was at the height of its influence, and traders carried the Phoenician alphabet to Greece.
From Greece, the alphabet went to Italy, Egypt, and Eastern Europe. By 900 B.C., the Phoenician system of writing quickly spread along the Mediterranean coast and into Asia. The Hebrews and their neighbors used a form of the Phoenician system in Palestine. Another form of the Phoenician alphabet spread to the area of present-day Yemen, and on to what is now called Ethiopia. Unfortunately, just as the unique alphabet spread around the world, Alexander the Great destroyed the city of Tyre by filling its prosperous harbors with silt and killing or enslaving its inhabitants. However, the Phoenician alphabet lived on.
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.
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.
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 which 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 which 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.