Art Education: Types of Pigments

Types of Pigments

Natural Organic Pigments

For today’s artists almost every natural organic pigment has been replaced by a synthetic organic alternative. These pigments only survive in their quaint historical names, which commercial paint companies use to lend romance to their modern mixtures. To determine the actual pigments in your paint tube, read the color index names listed on the paint label.

Madder was the many rose or crimson dyes from madder root which was native to Greece and cultivated extensively throughout Asia Minor. Madder was first manufactured as a laked pigment (madder lake)  around 1804, which greatly improved its permanence and also afforded an expanded range of colors depending on the specific salt or substrate used in the laking process: Two important pigments were first separated in 1826: orange purpurin and deep red alizarin. Both pigments are impermanent, but purpurin is especially fugitive, and is the source of genuine madder’s warm, fiery color. The bluest lakes were made by precipitating pure alizarin on alumina.

Carmine (New World cochineal) is made from the dried bodies of female wingless scale insects that feed on prickly pear or torch thistle cactus throughout Central America and Mexico. The carmine of antiquity (Old World kermes) was extracted from a similar insect that lives on scarlet oaks native to the Near East. Kermes carmine was used as a dye and a laked pigment in ancient Egypt and Greece and is one of the oldest organic pigments.  Cochineal carmine was used by the Aztecs and was first imported to Europe in the 1530’s from Spanish conquests in America. The dye is still available today as a food coloring, and carmine is one of the few red pigments considered safe enough for use in eye cosmetics in the USA.

Indian lake or lac is made from the blood red secretion of female scale insects that feed on the twigs of various trees native to India. The twigs become encrusted with a reddish, bumpy and glossy resin which is processed to extract the red colorant; lighter grades of the resin are used as the basis for shellac. Chemically lac is closely related to carmine, and is equally fugitive.

Dragon’s blood is a dark red resin exuded from the fruit of the rattan palm indigenous to eastern Asia; most often used as a colorant in varnishes, especially when applied over gold leaf, and is very fugitive.

Indian yellow was made from the urine of cows fed exclusively mango leaves. The urine was collected and evaporated, and the salty precipitate was rolled into balls which were exported for processing into pigment. The color is a deep yellow with a greenish fluorescence, but is only moderately lightfast.

Gamboge was a moderately saturated middle yellow pigment made from the gum of the several species of garcinia tree native throughout Southeast Asia but cultivated primarily in Cambodia and India.

Sap green was originally made from dried, ripe berries of plants in the buckthorn family.

Persian berries lake was made from dried, unripe buckthorn berries, and especially popular in France and England during the 18th century. These and similar pigments are very fugitive.

Stil-de-grain was a fugitive deep yellowish brown lake made from the inner bark of a species of oak indigenous to North America and commonly used in the 18th and early 19th centuries.

Indigo is an very old and widespread colorant made from the fermented gray green leaves and flowering stalks of over 30 related plant species native to India, Asia and Europe. The dye was used in China and India since 2000 BC, was known to ancient Egyptians as far back as the 16th century BC. The dye molecule was first artificially synthesized in 1870.

Van dyke brown originally was a brown pigment made from deposits of peat or brown coal.

Sepia was made from the ink of the cuttlefish found in the Adriatic Sea and was also made from walnuts.

Vine black is made from carbon obtained by burning wood.

Lamp black is a fine fluffy powder obtained by collecting soot from burning oils, etc..

Ivory black was made by slowly calcining ivory in hot ovens. All modern supplies are made from bone, as ivory is an internationally banned product.

Egyptian mummy or caput mortuum a tarry brown pigment was made from mummies excavated during the 18th to 19th centuries from ancient Egyptian communal tombs; these dried bodies had been embalmed with asphaltum (a petroleum residue) and resins.

Tyrian purple was made from a species of marine snail. It was the celebrated imperial purple of the Romans and Greeks. The dye was highly prized in ancient times, was prohibitively expensive and only afforded by the highest ranking aristocracy.

Iris green was the name of a lake made from the juice of iris flowers.

Safflower was a fugitive red lake made from dried flower petals of the safflower plant.

Saffron was the fugitive bright yellow color obtained from the dried petals of Crocus sativus used in Roman times.

Synthetic Organic Pigments

Synthetic organic pigments are carbon based molecules manufactured from petroleum compounds, acids, and other chemicals, usually under intense heat or pressure. The techniques for producing these substances on an industrial scale were invented after 1860, which created the modern era of consumer color.

Aniline, an oily, poisonous liquid chemical extracted from the distillation of coal tar compounds, was the jumping off point for a wide range of synthetic organic pigments. Many other dyes created from coal tar (and using ingredients other than aniline) soon followed, including the first artificial production of a natural dye: alizarin.

Originally, the aniline pigments as a group tended to be very fugitive, but the research into these early dyes involved modern organic chemistry and economic methods of colorant synthesis, which eventually provided all the synthetic organic pigments in use today.

Organic simply means “containing carbon atoms,” and the key to organic pigment chemistry lies in carbon’s amazing flexibility. It combines with itself in a great variety of atomic structures — rings, chains and branches — including the most important and basic, the benzene ring of six interconnected carbon atoms. These structures in turn can attach to each other, and to a variety of other atoms or chemical compounds (especially of nitrogen and hydrogen), to produce almost limitless molecular variations. Out of this chemical diversity come a large number of molecules with intense color attributes.

Many synthetic organic pigments, especially the azo pigments, are derived from water soluble dyes. The dyes are laked – bonded chemically to a colorless, transparent, insoluble salt that often acts as its own mordant – which turns the dye into an insoluble pigment. The most common base for modern laked pigments is aluminum hydrate, also used as an extender in oil paints; more opaque lakes are made with barium sulfate. Modern synthetic organic dyes can also be laked onto other relatively inert pigments, especially oxides of chromium, iron, tin or other metals, to increase the color of the finished product.

There several important groups of water insoluble, crystal pigments that do not require laking, including the phthalocyanines, quinacridones and vat dyes such as the perylenes and anthraquinones. (Vat dyes are insoluble unless mixed with specific chemicals)

Synthetic organic pigments are manufactured to be very potent and are often the most saturated and strongest tinting colorants available for any specific hue. However, they can be expensive to manufacture, and their lightfastness can change dramatically depending on particle size, crystal form, or the type of substrate used in laking. Synthetic organic pigments can also take on a variety of crystal modifications (especially in the phthalocyanines and quinacridones), and these can have very different color and lightfastness characteristics, although all are grouped under the same color index name.

Azo pigments form the largest, most diverse and most important group of synthetic organic colorants. Of the 336 currently manufactured synthetic organic pigments, 60% are in the azo family. From a noxious brewery come some of the brightest and most beautiful pigments ever discovered. Azo pigments can be made in almost any hue, but in practice the range is limited to the warm side of the color wheel: yellow, orange, red and brown.

Monoazo (arylide): A family of about 30 azo pigments, identified by the term arylide, providing almost exclusively yellow hues.  Arylide tinting strength not as strong as diarylide.

Disazo (diarylide): Another family of about 30 azo pigments developed around 1940, identified by the term diarylide, and (like the monoazos) providing mostly yellow hues of special significance to the printing industries. The three orange hue diarylide pigments are relatively impermanent.

Disazo Condensation: A small group of 17 azo pigments formed, like the diarylides, of two coupled arylide molecules: but these are joined in condensation with a bi-functional hydrocarbon molecule — hence the name. The few available as artists’ colors are semitransparent, have high tinting strength, and are typically very lightfast (more lightfast than monoazo pigments, though also more expensive).

Benzimidazolone: An important group of about 20 azo pigments with a broad range of hues; from yellow through orange and red, to a maroon of good lightfastness. Developed and patented by Hoechst in 1960, they are relatively expensive, but are also among the most durable pigments used in artists’ paints.

Beta Naphthol A relatively small group of azo pigments, among the oldest synthetic organic pigments, providing primarily red and a few orange hues. First produced around 1870, today only a few of these colors are still used, primarily because they are cheap to manufacture and moderately lightfast.

Naphthol: Developed in 1911, the naphthol compounds represent the single largest group of azo dyes and pigments. (In fact, about 20% of all synthetic organics available, over 50 in the red category alone are naphthol pigments.) They were first used in artists’ colors in the 1920’s. The most important group for artists is the naphthol AS pigments. The color range is concentrated in the long wavelength end of the spectrum, including warm orange, scarlet, many reds, carmines, maroon violet and brown. Can bleed in organic solvents.

Isoindoline & Isoindolinone: These are high performance, specialized forms of diazomethane pigments, in the azo group, first offered commercially in the 1960’s. Less than a dozen are available, in colors that range from yellow to orange and red. Although they are not widely used in artists’ colors at present, it’s likely that continued refinements on these compounds will create important new lightfast pigments for future artistic use.

Triarylcarbonium: Two groups of triphenylmethane pigments, obtained by laking basic dyes. The useful colors are green, blue, red and violet. Some shades are mildly fluorescing and are still used for their brilliance, especially as unlaked basic dyes (for example the rhodamine B, BV10, used in Holbein’s opera). Their lightfastness ranges from poor to worthless and no paint containing these pigments or any unlaked basic dye should be used in professional quality artworks.

The following do not require laking:

Phthalocyanine: Available as both copper and metal free phthalocyanine. Its blue shade has similar properties to Prussian blue and has replaced it on most artists’ pallets. It was commercially introduced in 1935 as monastral blue; the green shades in 1938. The phthalos form complexes with nearly every heavy metal atom (66 different metal complexes are known). The colors used in artists’ paints range in hue from a reddish blue to greenish blue, cyan, turquoise, bluish green and yellowish green; only the metal free form (PB16, a dull greenish blue) is a true synthetic organic pigment. The natural scarcity of blue and green pigments is illustrated by the fact that phthalo blue is the most important blue pigment discovered since cobalt blue (1804) or ultramarine blue (1828); phthalo green is the most important green pigment since emerald green (1814) or viridian (1838). It is a very strong pigment and it is normally reduced from 50 to 75% with alumina hydrate or blanc fixe.

Quinacridones: A large family of modern, moderately saturated and highly colorful pigments, recognized as useful pigments until 1955. They contain two pair of oxygen and nitrogen atoms set in five interlocking rings of carbon, hence the name “quin” for five. The first quinacridones were marketed in 1958 as artists’ paints. The available hues range from golden yellow, through reddish orange, coral, red, rose, magenta, maroon and a dark reddish violet. Nearly all quinacridones have excellent lightfastness ratings. Much of the color variation arises from differences in the way the quinacridone molecules combine into crystals, which can be altered through grinding with salts or heating in solvents. All quinacridones are nontoxic, mid valued and transparent.

Perinone: A handful of important vat dyes that have been known since the 1920’s, but have been available as pigments only since the 1960’s. Hues cover a relatively limited range, including perinone orange and the somewhat dull perinone red deep. Perinone orange has good lightfastness and (when combined with aluminum flake pigments) makes a fine copper metallic paint.

Perylene: Described and used since around 1912 as vat dyes that are chemically related to the perinones, the perylenes were first manufactured and sold commercially as pigments in 1957. Available colors are limited to moderately saturated scarlets, reds, dark maroons and a very dark green. All the perylenes are nontoxic, mid valued, transparent with very good to excellent lightfastness.

Anthraquinone: A small group of about 10 pigments, most of them with a long history as textile vat dyes. They made dull, weak pigments until methods of purification, careful precipitation and grinding were discovered that retained most of the dye’s color brilliance. The group includes anthrapyrimidine yellow, anthraquinoid red and indanthrone blue.

Diketo-Pyrrolo Pyrrole: A small but very important group of new synthetic organic pigments discovered in the early 1980’s and systematically developed into pigments with very good lightfastness. About six are currently offered, in the shades orange, scarlet, red and carmine. Pyrroles have also been crystallized with quinacridones to produce hybrid pigments.

Dioxazine: A small group of chloranil derived colorants with one very important color, dioxazine violet, developed in 1952 as a dye. The pigment is obtained by dissolving the dye in a very hot acid, then washing and salt grinding the precipitate that results. It has “very good” to” excellent” lightfastness.

Thioindigoide: A red vat dye pigment often called permanent red or garnet lake. It is a relatively clean color with excellent lightfast properties.

Natural Inorganic Pigments

Natural inorganic pigments are among the oldest used by humans. They first appear in the funeral preparation of human remains from 60,000 years ago and in polychrome cave art from about 20,000 years ago. Mined in prehistory from surface deposits of clay and rock, many inorganic pigments have shown extraordinary permanence over long periods of time. With few exceptions, inorganic pigments are combinations of a mineral element with oxygen and other elements (most often sulfur, silicon or carbon) that fall in the chemical classes known as oxides, oxide hydroxides, sulfides, sulfates, silicates and carbonates.

Red Earths: A large and diverse category of pigments, all made from earths (mostly clays) containing large proportions of iron oxide.  The pigment color may range from a dull yellow through a dull deep yellow, dull orange, dull red or dark brown. The color depends on the average particle size, the presence of manganese or other elements and whether water is chemically bonded within the iron oxide crystals. The dull red orange to yellow hydrous oxides contain water, the maroon to dull red anhydrous oxides do not. These earths are often “burned” (calcinated or roasted at a dull red heat) to darken them (burnt sienna, burnt umber), a technique that was probably suggested around 2000 BC by the visible reddening or darkening of pottery after it had been fired or glazed. (Due to growing scarcity of high quality natural deposits of iron oxides, most artists’ colors are now made from synthetic iron oxides.

Yellow Earths: Natural earths containing silica and clay, hydrous forms of iron oxide and traces of gypsum or manganese carbonate. French ochre, historically one of the best grades of limonite, contains about 20% iron oxide and is high in silica. Currently workable deposits for yellow oxides are located in the Republic of South Africa and France. Most often sold as yellow ochre or brown ochre. Most yellow clays are normally not “burnt” as heat does relatively little to alter their color.

Green Earths: Clays containing large amounts of silica and the green minerals glauconite and celadonite, consisting essentially of hydrous iron, magnesium, and aluminum potassium silicates. Completely lightfast and chemically inert, green earth or terre verte has been used around the world since ancient times. In Europe, the first documented use in paintings is in Roman frescos; it was also commonly used in the Middle Ages as an underpainting for flesh tones and shadows.

Lapis Lazuli: A complex rock mixture of the deep blue mineral lazurite (natural ultramarine, chemically the most complex mineral pigment) with calcite or calcspar and iron pyrite. Lapis is found in China, Tibet and Central Asia, and used in jewelry, sculpture and painting in ancient Babylonian and Egyptian cultures.

Azurite: The less common (greenish blue) crystals of copper carbonate, called “mountain blue” (Bergblau) in Germany, which occurs in copper ore deposits around the world. Azurite has been used as a pigment since antiquity. An important pigment in Europe from the 15th to 17th centuries, it fell out of use when Hungary, the primary source of the natural pigment, was conquered by the Turks.

Malachite: The more common (green) form of hydrous copper carbonate, called mountain green, mineral green or verdeazzuro (“green azure”), found around the world in surface deposits of copper. The ancient Egyptians ground it to a powder for use as a green pigment; since Roman times the brighter synthetic copper pigments have usually been preferred for artistic uses. Used in European tempera and oil paintings from the 15th to 17th centuries; it fell out of use entirely by the end of the 18th century.

Synthetic Inorganic Pigments

Synthetic inorganic pigments are mineral compounds created through chemical manufacturing rather than by grinding and washing clays or minerals taken directly from the earth. The techniques for producing these substances on an industrial scale were developed after 1800, making them the first modern synthetic pigments of importance to artists.

Nearly all synthetic inorganic pigments were discovered or identified in the grand European flowering of inorganic chemistry that occurred in the century after 1750, when European industries sponsored intensive mineralogical and metallurgical research, and early chemists isolated and identified many new metallic elements — cadmium, cobalt, chromium, zinc, manganese, magnesium, and so on. Several synthetic inorganic pigments still used today, including iron blue, cobalt green, cobalt blue and zinc oxide, were discovered prior to 1800. These manufactured pigment compounds generally have excellent chemical purity and color consistency, and are cheaper to buy and available in larger quantities than natural inorganic pigments.

Cadmium Compounds: Cadmium paints were not commercially available until significant deposits of cadmium were developed around 1840. The first cadmium sulfide paints were marketed around 1842. Today the cadmium pigments range in hue from a bright, whitish lemon yellow through middle and deep shades of yellow and orange to scarlet, red, and dull crimson. The hue shifts result because the included metals expand (selenium, mercury) or contract (zinc) the average lattice dimensions within the cadmium crystals, placing the reflectance boundary at longer (“yellow”) or shorter (“green”) light wavelengths. Cadmiums are saturated, semi opaque to opaque, lustrous, dense and very smooth pigments, expensive but extremely permanent in pure form and if not mixed with lead or iron paints. The dark value of the reds makes them mix poorly with other colors, especially blues and greens. Cadmiums are considered mildly to moderately toxic.

Chromium Compounds: Chromium, a constituent of several green, yellow, orange and red pigments was discovered in 1797. The many related pigments include barium chromate, molybdenum chromate, zinc yellow and strontium chromate. Use of chrome colors began to decline steadily in the 20th century because most shades contain lead and the light yellow shades are impermanent and blacken when mixed with sulfur pigments. Among the greens, the hydrous (water containing) chromium oxide, commonly known as viridian, is a moderately saturated, weakly tinting, granular, transparent and moderately staining blue green. The anhydrous (water free) chromium oxide, usually sold as chromium oxide green. Chromium is also a compound in cobalt compounds such as cobalt green deep and the green shades of cerulean blue and cobalt turquoise.

Cobalt Compounds: Cobalt produces the most diverse range of pigments currently used in artists’ paints: its colors range from cobalt violets through several shades of cobalt blue, two shades of cobalt turquoise, several varieties of cobalt green, and cobalt yellow — even a grayish cobalt black. Cobalt blue has been used since antiquity in porcelain or glassware, and as a pigment (smalt) since the late Middle Ages. The first modern cobalt paints date from around 1835. All cobalt pigments are manufactured by calcining (roasting at extremely high temperatures) a mixture of cobalt oxide with an alkaline carbonate and, to produce the various colors, compounds of other metals (phosphorus, aluminum, tin, chromium, titanium, zinc or potassium). These pigments are semitransparent, moderately saturated, and very permanent.

Copper Compounds: Historically copper is a major source of blue or green pigments, which only recently have been available as lightfast synthetic organic compounds. The natural mineral forms chrysocolla (hydrated copper silicate), malachite and azurite were known and used since antiquity. Copper is more important as a constituent of several impermanent, synthetic inorganic green pigments. Verdigris is an ancient pigment manufactured by exposing copper strips to acetic vinegar. Scheele’s green was discovered around 1775 and it was the first modern synthetic green pigment. Schweinfurt green is an intense, light valued, blue green compound of arsenic and verdigris and commercially manufactured from public recipes after 1822 under a variety of names — Vienna green, King’s green, Paris green and Emerald green. All these synthetic copper compounds fell out of use by the mid 20th century because they have very poor permanency and because those containing arsenic are extremely toxic. Copper is also the metallic atom in the green azomethine pigments and the green and blue phthalocyanines, all described in the section on synthetic organic pigments.

Iron Compounds: Iron represents an extraordinarily old, widespread and versatile family of relatively dull but extremely permanent and nontoxic pigments. All the common iron oxides have been used since antiquity. Its manufactured use in artists’ paints did not emerge until the middle 19th century. The purest and finest oxides are produced from the precipitation and hydrolysis of iron salt solutions; hue and tinting strength are affected by hydration, particle size and by the presence of additives such as manganese. They can also be mixed to match precisely any yellow, orange, red or brown hue, including near black browns. For these reasons the natural pigments have been almost entirely replaced by synthetic oxide mixtures, currently marketed in watercolors under the names venetian red, english red, indian red, or light red and mars yellow, but are now also used in hues formerly made of natural red or yellow iron oxides.

A more exotic iron pigment is iron blue (hydrous ferriammonium ferrocyanide, sometimes with sodium or potassium ions substituted for the ammonia ion) known to 18th and 19th century artists as Prussian blue, Berlin blue, Paris blue, Milori blue or Chinese blue. This is the first modern synthetic inorganic pigment, discovered by chance in Berlin in 1704 when a color maker attempted to make a crimson pigment from cochineal, alum, ferrous sulfate and potash that was contaminated with animal blood.  The label “Chinese” derives from the blue patterns on Meissen china. The majority of artists now prefer the more intense phthalocyanine pigments. It has excellent lightfastness, but it loses permanency if mixed with impurities such as potassium ferrocyanide or with titanium dioxide. The pigment Prussian green is a fused matrix of iron blue and lead chromate; cyanine blue is a mixture of iron blue and cobalt blue.

Lead Compounds: These have been discontinued in most paints because of their excessive toxicity. They will darken when mixed with cadmium pigments. Historically important forms of lead are primarily red (lead tetroxide), yellow (lead tin oxide) and white (lead carbonate mixed with lead hydroxide and/or lead oxide and lead sulfate).  These pigments have been used in Europe and China from antiquity up to the present day. Both lead carbonate (as flake white or cremnitz white) and lead antimony (naples yellow, have marvelous pigment attributes. Lead white is probably the most important white pigment in the history of painting, and is still favored in oil paints for its warmth, opacity and buttery handling. Lead pigments turn black in the presence of sulfur (urban air pollution) so the finished painting must be varnished.

Magnesium Compounds: Historically, magnesium is most important as magnesium euxanthate, commonly called peoli, gaugoli or indian yellow. In daylight the fresh color fluoresces in “yellow green” wavelengths; this combines with a deep yellow pigment color to produce a unique luminescent, duo-toned golden yellow hue. This synthetic inorganic pigment was made from the urine of cows fed on mango leaves; crystals of the concentrated dried urine were formed into balls and covered with mud for shipment to England. The pigment was displaced by the new cadmium yellows, cobalt yellow (which often inherited the name “indian yellow”) and gamboge.

Manganese Compounds: An important but shadowy mineral, currently found mostly as a secondary component of many blue, green and iron oxide pigments. The most important pigment is manganese violet (manganese ammonium pyrophosphate), which was offered as an artists’ pigment until 1890. It is a moderately saturated, granulating, semitransparent purple. Manganese blue (barium manganate) is a weakly tinting, moderately saturated, granular, semitransparent and greenish blue, a near perfect cyan for the subtractive “primary” colors. Many manufacturers offer a “manganese blue hue” made from phthalocyanine.

Mercury Compounds: The earliest mercury pigment is natural mercuric sulfide, found in the mineral cinnabar, the primary ore of mercury, and used as a pigment since Roman times. Synthetic mercuric sulfide or vermilion was widely used in European oil painting up until 1850’s. The color is a bright, opaque scarlet red. It is not a satisfactory pigment by modern standards because it is highly toxic (mercury will cause severe metal poisoning) and fugitive (it quickly withers to a dull brown in the presence of light). Modern substitutes (“vermilion hue”) have been formulated of cadmium scarlet. Iodine scarlet (mercury iodide in 1814 and sold in England under the name scarlet lake, is a brilliant orangish red — unfortunately very fugitive and extremely toxic.

Sulfur Compounds: Sulfur is a constituent of many pigments, including arsenic, cadmium, mercury, chromium and lead. It has always been a troublesome chemical, because of its tendency to blacken other metallic pigments it is mixed with. The most poisonous of these pigments — arsenic sulfide or orpiment, mercury sulfide or vermilion, and lead sulfate are no longer used in artists’ materials.

The most important sulfur pigment is sodium aluminum sulfosilicate or ultramarine blue which is chemically identical to the principal pigment in natural lazurite. The artificial form was first noticed by in 1787 as a residue in Italian lime kilns near Palermo. By 1830, it was being produced on a commercial scale and immediately adopted in artists’ colors. It is a dark, moderately intense, semitransparent and staining pigment varying in hue from a greenish blue to a blue violet. Ultramarine is manufactured by heating a finely powdered mixture of china clay (kaolin), soda ash (sodium sulfate and/or carbonate), charcoal, silica and sulfur in closed crucibles for about 21 days, up to a temperature of about 750°C after 7 days; this results in a green, glassy matrix that turns deep blue if it is exposed to oxygen as it cools. The matrix is then crushed, washed, dried and ground. The final hue depends both on the exact proportion of ingredients and the amount of heating and all ingredients must be free of iron. All hues are very lightfast.

Titanium compounds: Titanium dioxide is the supreme white pigment: no other compound matches its scattering properties (whiteness), chemical stability, and lack of toxicity. Nearly 5 million tons were manufactured in 2000, mostly by factories in Asia and Australia; because of its extremely high refractive index it is the principal opacifying and color brightening ingredient in a wide range of architectural and crafts paints. Two manufacturing processes are used: both involve sifting or grinding natural titanium sands or recycled titanium slag, soaking the raw materials in a heated, reducing acid or chloride bath, separating out impurities through a sequence of chemical reactions followed by centrifuging or filtering, and grinding to finished particle size. A beautiful range of light valued cobalt greens and turquoises has been created by incorporating cobalt and titanium atoms into crystals of magnesium aluminum oxide; these pigments have a characteristic whitish hue that is integral to the pigment crystal and therefore extremely permanent.

Zinc compounds: Zinc sulfide was developed in 1850 as a white pigment used in oil based paints. Zinc oxide, a byproduct of copper smelting, was known to the Romans (who called it cadmia), but they used in primarily as a skin ointment (it is still used today for sun block and sunburn). Winsor & Newton marketed an especially dense form (manufactured by burning the metal at much higher temperatures) as “chinese white.” It has entirely replaced lead white in watercolors and acrylics, although it tends to dry to a brittle film in oils. Zinc also combines with cobalt to produce a lovely deep blue cobalt color. Finally, zinc green, consists of zinc chromate with ferrous ferrocyanide (iron blue).

Synthetic inorganic pigments are among the most lightfast pigments available. Some of them are also the most expensive pigments you can buy, which means that some manufacturers add fillers to reduce the amount of pigment used in the paint. The paint may have a good lightfast pigment, but it is when adulterated with excessive filler, the tinting strength of the pigment is diminished and the pigments brilliance is greatly diluted.