Understanding Pigment

Color Index

The Color Index is an internationally recognized standard of pigment classification. There are many different names given to pigments and the paints made from them. These names often have little or no relationship with the pigment or chemicals used to make the paint. Pigments often have a shade range within the same mineral and each shade will have its own common name. For instance, red iron oxide may have five different shades with the same CI number. This is why the Color Index was developed. The Color Index gives the pigment's usage designation and hue (often abbreviated) plus a unique serial number, such as, Natural Red 8 (NR8)--Alizarin Crimson and Pigment Blue 29 (PB29)--Ultramarine Blue. 

All these different names for the same paint can be confusing, especially when a company uses two or more names for the same color to increase their sales. A pigment may also be sold under different names by different companies to distinguish their paint from the competition. A company may also have several lines of varying quality grades, each with a different formula under the same name. Some pigments work with certain binders and additives better than others as well.

Without the pigment name or CI number, you have no way of knowing what's in the paint. If you pay $50 for a 37ml tube labeled Cerulean Blue, it should also have PB35 on the label. If it reads PB36, it's Cobalt Chromite, a chemical substitute. Phthalo Blue mixed with Titanium white doesn't have a CI. If the label doesn't point out the exact hue or substitute, you could be getting ripped off. 

The American Society for Testing and Materials (ATSM) demands that manufacturers print the Color Index on the label of oil (D-4302) watercolor (D-5067), and acrylic (D-5098) paints. Plaid only conforms to ATSM D-4236 which means they adhere to health hazard and toxicity labeling only.

The Art Pigment Database cross references paint numbers with the oxides or minerals they are made with. Only manufacturers who adhere to ATSM CI standards are listed in the database.

Clay Pigments / Mineral Ochres

Minerals are traditionally used in oil paint, but may also be used in acrylic with a wetting agent. They are very stable and can be used in any media. They can also be mixed with Ultramarine pigments.

Most ochres come from the last remaining company in Europe to mine deposits in the French quarries of Gargas and Rustrel, nestled in a twelve-mile long enclave in the heart of the Luberon Mountains. Also known as Ochre Country in Provence, these deposits have been registered by the Government of France as protected and classified Natural Sites. Ochre (from the Greek word Okhra, meaning yellow soil) is a naturally occurring clay in a symphony of colors ranging from pale yellow to tobacco brown.

Different colors of ochre are mined in different locations. All ochres contain ferric oxide or iron as their primary component which is colored according to the concentration of other minerals. Yellow ochre is hydrated iron hydroxide or limonite. Red ochre is anhydrous iron oxide or hematite found above iron deposits. Pink ochre or catlinite is hematite that was leached into clay beds. Augit Porphyry is the same as red ochre, but it contains light defraction properties and large particles that change the hue. Brown ochre is partly hydrated iron oxide or goethite. Raw sienna contains limonite and less than 5% manganese. Raw umber contains 5-20% manganese. Burnt sienna and Burnt Umber is heated limonite. Green earth is iron potassium phylosilicate or glauconite. The color range is yellow-green, green and blue-green. Gray Green Ochre is the hydrous aluminum silicate of iron also known as chamosite that is mined in Switzerland. It is used in making graphite pencils and marketed as pencil clay. As a pigment or paint, it is called Davey’s Grey. Blue earth is hydrated iron phosphate or vivianite from Russia. Purple ochre is calcined hematite tinted with iron oxide from Armenia. Light brown ochre is iron carbonate or siderite. Black oxide is ferrous ferric oxide or magnetite found near iron deposits. 

Exceptions: Gray ochre or slate is hydrated aluminum silicate or kaolin found near shale deposits in France. Vicenza earth or buff ochre is hydrated alumina silicate or kaolin from Italy. Antwerp Brown or Bitumen is a naturally occurring resinous hydrocarbon known as asphaltum or gilsonite that is mined from deposits in Utah. Plumbago or graphite is a crystalline form of carbon. It was used in the 4rth millennium BC by the Marita culture of southeastern Europe in a ceramic paint for decorating pottery. Black ochre is an amorphous variety of graphite found in a matrix of carbon. It is also known as shungite and is mined in Russia.

Ochre must go through several important steps to become available for use. First, the ore must be extracted from the cliffs in the quarries. The ochre is then separated from the sand using water and centripetal action for this cleaning procedure. The ochre is then dried in the open air from spring through summer before being stored. Some colors will undergo calcinations. For example, raw yellow ochre is heated at high temperatures to obtain burnt sienna. Mixing different ochre pigments extracted from diverse veins creates a unique and exclusive range of colors. They are then pulverized and packaged for use. 

Ochre extraction at the Luberon quarries is a well-controlled mining process, paying strict attention to the environment. Air pollution is prevented by the use of dust removal devices installed in the factory's chimneys to clean the smoke before it is released into the air. A high volume of water is necessary to clean the ochre. Running in closed circuits allows for cleaning and recycling of this water. The separated sand, when not sold for different purposes, is returned to its original site. Extraction is done by machine, employing the technique of terracing to maintain structural integrity. Mined sites are then rebuilt with their original top layer of soil.

Indian Red Ochre = Hematite

Red Ochre = Iron

Raw Sienna = Limonite + <5% Manganese

Burnt Sienna, Burnt Umber = heated limonite (P R7)

Yellow Ochre = Limonite (PY42)

Ancient Green Earth, Verona, Nicosia, Tavush = Glauconite

Gray Green Ochre = Chamosite

Blue Earth, Blue Ochre = Vivianite

Violet Earth, Purple Ochre = Hematite + Calcium

Augit Porphyry, Red-Blue Oxide = Hematite (PBR6)

Light Brown Ochre = Siderite

Raw Umber = Limonite + 5-20% Manganese (PBR9)

Van Dyke Brown, Cassel's Earth, Dark Umber = Goethite (NBR8)

Antwerp Brown, Bitumen = Gilsonite (NBK6)

French Slate, Grey Ochre (PBK19) = Kaolin + Shale

Plumbago = Silver, Black Graphite (PBK10)

Black Oxide = Magnetite

Black Ochre = Shungite

Buff Ochre, Vicenza Earth = Kaolin (PW 19)

Mars Oxides

The bright new inventions of 19th century chemistry, Mars colors, from Red to Violet, ignited a color revolution in painting by placing clean, concentrated man-made earths on the palette. Today, these pigments are made with sludge produced from ochre mining.

There are many names for hydrated oxides, usually based on color, production location, mining site, or manufacturing method, followed or prefixed by other properties such as raw, burnt or transparent etc. There are also variances on the words oxide (Oxyde, oxid, etc.), Iron (di ferro, de fer, mars, Ferric, ferrous, etc.) and yellow (amarillo, juane, geel, gelb, lemon, citron, mustard, etc.). The oxide pigments have an ancient history and because pigments often still use the traditional name, a multitude of languages have intermixed becoming an almost impossible list of varied phrases.

The modern Mars pigments, called Transparent Iron Oxides, bring both warmth and brightness to a mixture.

Mars Red, Transparent Red Oxide (PR101H)

Mars Orange (PY42)
Mars Yellow, Transparent Yellow Oxide, Felsite (PY42H)

Mars Violet

Transparent Brown Oxide, Cinnamon Brown Oxide (PBR6)

Umber Oxide (PBR7)

Mars Black (PBK11)

Geological Pigments

These are stones such as lapis lazuli, malachite or azurite which are ground fine enough to use as a pigment. These provide the brilliant colors you see on frescoes. Such pigments can still be purchased (often you will find them listed under 'historic colors') but they are very expensive and can be quite difficult to paint with. Ultramarine, the original name for lapis,  means “beyond the sea” because it was mined in Afghanistan. Even today, the best AAA grade lapis pigment costs $30,000 per 1,000 pounds. It was synthesized in 1826. Some stones lose their color when ground too fine and a gritty texture is the price you pay for that beautiful scintillating hue. On the other hand, azurite is better the finer it is ground. I recommend purchasing stones or powder from a lapidary or rock shop. The original ultramarine was lapis, but it was so expensive that Rembrandt chose to use smelt instead. Smelt fades badly over time and this is why there is almost no blue or green in Rembrandt’s paintings. Today, smelt is more expensive than the synthetic ultramarine that replaced lapis. Gold, silver and copper fall under this category because, even though they are metals, they are technically elements. Gold was used to produce illuminated manuscripts.

To extract pigment from rocks, first crush AAA jewelry grade rock into pea size gravel. Grind with water into a powder of less than 50 microns. Wash and allow to dry. This powder is referred to as “ash”.

1 lb. stone ash

2 oz. Gum Mastic

6 oz. Gum Rosin (pine resin)

4 oz. Beeswax

Depilatory wax melter 

Silicone pastry mat

2 bowls

Fine mesh sieve

Coffee filters

Melt the gums and beeswax. Add powder and stir to combine. Pour the mixture onto a silicone mat. When cool enough to touch, peel it off the mat and knead until it is an even consistency. Roll into a 1” log and cut into 12” lengths. Allow sticks to sit for 3 days. Soften logs 1-3 at a time in hot water (230 F). Knead each log again and reshape into a log. Allow to rest for 24 hours. Soak a log in a bowl of warm water while massaging it. The beeswax and gum will hold the impurities and release the pure pigment that settles to the bottom. This takes about 4 hours per stick. Strain the water into another bowl through a very fine sieve. Pour the pigment out of the bowl and spread it onto coffee filters to dry. Once dry, it can be bottled or used for paint. 

Use the water to make water based paint or dye. Each stick can be processed twice, resulting in a lighter color. Stop when a bowl of clean water remains clear.

This is the way it was done in the 14th century. I suggest starting with B grade stone to get a feel for the process. 

Malachite (No CI)

Lapis Lazuli aka, Fra Angelico, Ultramarine (No CI)

Azurite (No CI)

Smelt (No CI)

Gold (Element)

Silver (Element)

Copper (Element)

Pigments from Metals

Metal pigments are technically geological or stone pigments, but they are closer to the ore and produce crystals or may be the actual ore. These pigments along with stones were historically used in oil paint. They may still be used with caution. Don't inhale the powder or touch it without gloves and don't get the paint on your skin. These pigments should not be exposed to extremely high temperatures.

Cinnabar, the source of vermilion contains mercury. Rarely used, restricted to preserving historic artwork.

Cerussite or Lead Carbonate, the source of lead white, causes lead poisoning after cumulative exposure. Rarely used, restricted to preserving historic artwork. Lead ore produces galena, silver lead, gold lead, crystal lead and cerussite.

Queen Elizabeth I painted her face, neck, décolleté and hands with lead carbonate paste after recovering from small pox. It may have shortened her life, but it also became a trend that lasted through the Renaissance. It was replaced with Titanium dioxide which evolved into women wearing colored makeup in the late 1800s.

Nickel, the source of Naples yellow leads to poisoning and nerve damage with cumulative exposure. Rarely used, restricted to preserving historic artwork.

Orpiment, arsenic sulfide, is a rare mineral that forms with realgar (the orange hue of arsenic sulfide). Both orpiment and realgar were used in Egypt from the 31st-6th century BC. Arsenic was used to produce Paris Green or Emerald. It is a mint green color with a slightly yellow tint. It was used to dye clothing and wallpaper. Many children during the Victorian Era died in their nurseries, suffocated by the toxic vapors released by the wallpaper in their rooms. Arsenic sulfide is highly toxic and cannot be handled without gloves and a mask. Rarely used, restricted to preserving historic artwork.

Cadmium can not be passed from the human body after inhalation. All cadmium pigments become highly toxic through burning, during which low soluble cadmium sulfide is turned into cadmium oxide, which can easily be absorbed into the body. Commonly in use by artists, but is being replaced with synthetic.

Cobalt is harmful if inhaled or swallowed and dangerous in cumulative effects. Commonly in use, including makeup.

Ferric Ferrocyanide, the source of Prussian blue produces highly toxic hydrogen cyanide gas if heated to high temperatures or treated with acid or ultraviolet radiation. It was found on Nazi chamber walls as evidence of cyanide gas poisoning. Commonly in use, including makeup.

Phthalocyanine blue and green from copper is harmful if inhaled or swallowed. Commonly in use, including makeup.

Manganese: Cumulative exposure leads to nerve damage. Commonly in use, including makeup in the form of Manganese Violet, Murasaki Manganese and umber oxides.

Barium sulfate is the only heavy metal considered to be non toxic because of its insolubility. It is frequently used medically in X-ray imaging of the GI tract and is readily removed from the body. It is used as a coating (baryta) on photographic paper to increase its reflectiveness. It is also combined with zinc sulfide to create lithopone, a transparent white paint.

It's okay to use some of these pigments for makeup, so long as it isn't ingested, meaning they can't be used in lipstick. Eyeshadow safe pigments are marked with an asterisk (*).

Vermilion from Cinnabar (PR106)
Cadmium Red, Red Violet, Maroon, Brown (PR108)
Cadmium  Orange (PO20)

Cadmium Yellow (PY35)
Nickel Yellow, Naples Light Yellow (PY53)

Cadmium Medium/Deep Yellow (PY37)

Naples Deep Yellow (PBR54)

Jaune Brilliant non toxic sub for Naples Yellow (PBR24)

Cadmium Green (PY35)

Cobalt Light Green (PG50)*

Phthalo Green (PG7)*

Cobalt Green (PG26)*

Cobalt Blue or Green, Light and Deep Turquoise (PB36)*

Phthalo Blue (PB15)*

Phthalo Blue, Red shade (PB15:1)*
Phthalo Blue, Green shade (PB15:3)*
Cobalt Blue (PB28)*
Prussian Blue or Ferric Ferrocyanide (PB27)*

Cobalt Tyrian Violet (PV14)*

Manganese Violet (PV16)*

Murasaki Manganese*

Iron Black (ferrous sulphate)

Lithopone White (PW5)

Biological Pigments

These are colorants derived from burned animal bone, insects, mollusks or even human corpses. Tyrian purple was made from the glands of sea snails. It takes 2,000 mollusks to produce 1 ounce of pigment. The reason for the lack of mummies in Egypt is because they were used to make pigment. It was a desirable color for skin tones, but paint makers quickly ran out of mummies. Indian Yellow is rumored to have been made from the urine of Brahma cows that were fed only mango leaves, but I believe they were fed whole mangoes. Soil that absorbed the urine was collected and ground to produce the pigment. It has a 2-in-1 color effect. It begins like opaque yellow ochre and dilutes to a bright lemon yellow which is a color change unheard of with any other pigment.

The sugar-based economy of the Canary Islands faced stiff competition from Spain's Caribbean colonies. Low sugar prices in the 19th century caused severe recessions on the islands. A new cash crop, cochineal (cochinilla), came into cultivation during this time, saving the islands' economy. 

Crimson: dead and powdered Kermes insect that lives on Kermes or Ilex oak trees = wine, fuchsia, pink; replaced by cochineal (NR3)

Carmine: dead and powdered cochineal insect that lives on prickly pear cactus = wine, fuchsia, pink (NR4)

Shellac: live insect secretion = bright pink (NR25)

Red Indigo: Lichens (Rocella tinctoria) (NR28)

Indian yellow: Mango fed cow urine

Royal Purple: Banded Dye Murex (Hexaplex trunculus)(blue violet, purple)

Tyrian Purple: Spiny Dye Murex (Bolinus brandaris)

(berry, plum purple)

Royal Red:: Florida Dog Winkle (Stramonia haemastoma) (fuchsia, scarlet red)

Description

Sepia: from the ink sac of Adriatic cuttlefish (NBR9)

Mummy Brown from ground Egyptian mummies

Boiled Leather is a substitute for mummy brown.

Ivory/Bone Black: burnt elephant tusk, animal bone (PBK9)

Botanical Pigments

Chrozophora tinctoria fruit shell, aka, Dyer’s Croton, Turnsole or Folium was the blue and purple used on medieval manuscripts. The berries were stored on cloth and dried. When it was time to use them as paint, a piece of cloth was cut and the paint was extracted with water or another element to bind it to the page. It is also used as a red food colorant in Dutch cheese and certain liquors. A hermidin alkaloid in the berry is responsible for the blue color. The chemical is also found in another medicinal plant, Dog’s Mercury (Mercurialis perennis). In the year 2020, the pigment was extracted by scientists and given the name, chrozophoridin. It is neither an anthrocyanin nor a leucine; it is in a class by itself.

These are colorants derived from plants. All paint made from botanical pigments are translucent and fugitive. They function best as writing ink and dye. Food and cosmetic safe pigments are marked with an asterisk (*).

Activated Charcoal (black)*

Alder Buckthorn Bark (mustard yellow, cinnamon red)

Alkanet (purple, mauve, lavender)* (NR20)

Annatto (yellow-orange, cream)*

Beetroot (pink, burgundy)*

Blackberries (red-violet, burgundy)*

Blueberries (blue, violet)*

Boysenberries (purple)*
Brazil Wood (pink-deep crimson) (NR24)

Buckthorn unripe green berries, Rhamnus saxatilis (Persian) or infectoria (American) = sap green

Buckthorn ripe black berries, Rhammus cathartica (French Avignon) or infectoria (American) = gold (green overdyed with indigo, black overdyed with logwood)

Butterfly Pea Flower* (deep blue) Clitoria ternatea changes color with pH. Adding lemon juice will turn it purple. Mixed with fuchsia roselle hibiscus leaves, it will turn a bright red.

Carrot root (red, orange, yellow, purple)*

Chayroot: Red Madder (red, coral) (NR6)
Chicory leaves (blue)*

Chlorella (green)*

Chrozophora tinctoria fruit shell* (blue, purple) Adding lemon juice will turn it purple.

Cranberries (light true red)*

Coreopsis (yellow, orange, brown)

Cutch heart wood (fawn, peach, khaki, warm golden brown)

Dock root (olive yellow)

Dragon's Blood (maroon) (NR31)

Dyer's Chamomile, Anthemis tinctoria (yellow, yellow-green overdyed with woad)

Dyer's Greenwood (yellow, Kendal green overdyed with woad)

Dyer's Woodruff root (red)

Elderberries (burgundy, wine)*
Fustic liquid (gold, peach)

Aleppo Gallnuts = Iron Gall ink (brown)

Gamboge (bright yellow) Garcinia hanburyi resin

Goldenrod (yellow)

Henna (tan, ivory)

Hibiscus (red, burgundy)*
Himalayan rhubarb (olive)

Indigo (pale-deep blue)

Indigo Carmine (medium blue)*

Japanese indigo (dark blue)

Kamala (Indian yellow or brown warss) memecylon tinctorium

Ladies Bedstraw (pale red) used in place of rennet for cheese 

Lichens: Roccella tinctoria (Pirineus Green)

Logwood (lilac, purple, plum, black)

Mahogany Wood (reddish brown)

Mushrooms, various species and colors
Myrobalan (khaki)

Oak Galls = Iron Gall ink (brown)

Onion skin, yellow (brown when boiled)*

Onion skin, red (bronze when boiled)*

Osage Orange (yellow)

Paprika (deep red orange)*

Poke berries (magenta, purple) Toxic!

Pomegranate rind (pale-golden yellow)*

Quebracho rojo (red)

Quebracho moreno (orange)

Raspberries (pink, red)*

Red Bell Pepper (bright red orange)*

Red Cabbage (purple)*

Red Cabbage + 1/2 tsp baking soda (blue)*

Rhubarb root (orange, yellow)* leaves are a mordant (NR23)

Rocky Mountain Bee Weed or Wild Spinach (black)

Rose petals (bright pink)*

Saffron (yellow-orange)*

Safflower (red, orange, yellow)* (NR26)

Sandalwood (rust, orange, peach, brown) (NR22)

Saw-wort (lemon yellow)
Saxon Blue Indigo liquid (aqua blue)

Schisandra berries (deep true red)*

Spinach (bright green)*

Spirulina (deep green)*

St. John's Wort flowers (maroon, yellow, green, brown)

St. John's Wort tops (beige, brown)

Strawberries (pink, red)*

Tansy (pale golden yellow)

Tomatoes (light red orange)*

Turmeric (deep yellow)*

Walnut hulls (brown)*

Weld (bright lemon, Lincoln green over dyed with woad)

Woad (Venetus Blue)

Leuco Pigment

Leuco is just a fancy word to describe botanical pigments that change color when they oxidize. Indigo and Woad are two naturally occurring leuco dyes. Indigo is insoluble in water and therefore must be reduced with sodium hydrosulfite to an alkali soluble form and then chemically oxidized. This is called Indigo Lake and is generally the form we use today. Historically, slaves were transported from Africa to South America, the Caribbean, Louisiana and Florida because they knew how to work with Indigo. It was more economical for Spain, France and England to own indigo plantations in tropical regions than it was to trade with India or Asia. This was during the 16-17th centuries, the early colonial period. 

The leaves were soaked in water and fermented to convert the glycoside indican to indigotin. The precipitate from the fermented solution is then, mixed with lye making it a very dangerous process.

Indigo, though plant based, is completely insoluble in water, meaning that it cannot be applied to clothes directly. It is instead reduced with sodium hydrosulfite to indigo white (Leucoindigo), which is water-soluble but colorless. When a submerged fabric is removed from a dyebath of white indigo the dye quickly combines with oxygen in the air and reverts to the insoluble, intensely colored indigo. This is why the original Levis jeans never faded with washing. Woad is water soluble, but changes from blue to green with air exposure.

Synthetic leuco dyes are micro encapsulated compounds. The capsules have a very thin outer wall that hold the leuco dye, a weak acid and a solvent. The leuco dye used depends on the color desired. The solvent used depends on the temperature at which a color change is desired. All thermochromic inks are colored at cool temperatures and colorless at elevated temperatures. At a cool temperature the solvent inside the microcapsules is in the solid state. The leuco dye and weak acid are in contact with each other and the dye molecules are colored. In the liquid state, the dye and acid components disperse and the colorless form of the dye predominates.

Aniline Dyes

In 1840, Carl Julius Fritzsche treated indigo with caustic potash and obtained a yellow oil that he named aniline. In 1856, whilst trying to synthesise quinine, von Hofmann's student William Henry Perkin discovered mauveine and went on to produce the first synthetic dye. Aniline black dye was patented by J.Lightfoot in 1863. It is composed of oxidized aniline hydrochloride. Silk, was soaked in an aqueous solution of aniline hydrochloride and an oxidizing agent, such as chromic acid. This resulted in a strong black color that was not lightfast. Aniline black replaced logwood dye as an additive to iron gall ink to produce a strong, initial black color. Once the dye faded, the iron and gallic acid color had developed a strong black tone.

The principal use of aniline in the modern dye industry was as a precursor to indigo. Aniline dyes went on to become laboratory pH indicators. Today, they are used for dyeing animal or protein fibers, leather, shoe polish and staining wood.

Aniline Yellow

Safranine

Induline

Mauvine

Fuchsine

Aniline Black

Lake Pigments

Lake is derived from the word lac or shellac (referring to a resinous secretion by an insect) which is the source of the word, lacquer. Manufacturers frequently omit the lake designation in the name. Lake pigments have a long history. Some have been produced for thousands of years. These pigments are very bright and transparent. They were once used as glazes over mineral ochres because they were very expensive. Many lake pigments are fugitive meaning they are unstable when exposed to light.

A lake pigment is manufactured by precipitating a biological or botanical dye with an inert binder, or "mordant", usually a metallic salt. The metallic salt or binder used must be inert and insoluble in the vehicle, and it must be colorless or very neutral. The organic component of the dye determines which wavelengths are absorbed and reflected by the resulting precipitate. In ancient times chalk, white clay, or crushed bones were used as the source for the calcium salts. The salts that are commonly used today include barium sulfate, calcium sulfate, aluminum hydroxide, and aluminum oxide (alumina), all of which can be produced cheaply from inexpensive mineral ores. Many people have protested the use of aluminum in their cosmetics due to a metal allergy.

Lake pigments are used for food coloring, cosmetics, soap, alcohol inks, and transparent paint. You will often see them labeled as FD&C or D&C. This means the pigment is safe for use in food, drugs and cosmetics or just drugs and cosmetics, but not food. Both are used to make lip products and eyeshadow.

Madder lake, originally from chayroot, is known as alizarin crimson in its synthetic form. Since madder isn’t lightfast, its use has been largely superseded by quinacridone pigments. Alizarin was first synthesized in 1868 by the German chemists Carl Gräbe and Carl Liebermann.

Indigo Carmine is an organic salt derived from indigo through sulfonation which renders the compound soluble in water. It is approved for use as a dye, food colorant and a pH indicator.

Madder Lake, Turkey Red (NR9)

Crimson Alum Lake (Alizarin Crimson) (PR83)

Erythrosine FD&C Red #3/14/51 Acid Lake CI 45430

D&C Red #6 Barium Lake CI 15850:2

D&C Red #21 Alum Lake CI 45380:3

D&C Red (Pink) #27 Alum Lake CI 45410:2

D&C Red #30 Talc Lake CI 73360

D&C Red (Magenta) #33 Alum Lake CI 17200

Allura FD&C Red #40 Alum Lake CI 16035

D&C Orange #5 Zirc/Alum Lake

Tartrazine FD&C Yellow #5 Alum Lake CI 19140

Sunset Yellow FD&C Yellow #6 Alum Lake CI 15985

D&C Yellow #10 Alum Lake CI 47005:1

Brilliant Blue D&C Blue #1 Alum Lake CI 42090

Indigo Carmine D&C Blue #2 Acid Lake CI 73015

Azo Pigments

Chemically related to azo dyes are azo pigments, which are insoluble in water and other solvents. Azo pigments are hydrophobic and only miscible in oil or glycerin. Azo pigments are used for artists paint as an alternative to expensive geological pigments and deadly metal based pigments. They are more stable when exposed to heat and thus can be used to make pencil leads or any other media.

Azo pigments are similar in chemical structure to azo dyes, but they lack solubilizing groups. Because they are insoluble in virtually all media, they are not readily purified, and thus require highly purified precursors.

Azo pigments have excellent coloring properties, mainly in the red to yellow range, as well as good lightfastness. The lightfastness depends not only on the properties of the compound, but also on the way they have been absorbed on the pigment carrier.

Many azo pigments are non-toxic, although some, such as dinitroaniline orange, ortho-nitroaniline orange, or pigment orange 1, 2, and 5 are mutagenic and carcinogenic.

These pigments are not used in lipstick. Eyeshadow safe pigments are marked with an asterisk (*).

Naphtol Red (PR2)

Naphtol Crimson Red (PR7)

Permanent Red (PR8)

Cadmium Red Imitation (PR9)

Toluidine Red, Azo Red, Chinese Red, Vermilion (PR3)

Pyrrole Red (PR254)

Anthroquinone Red: Alizarin Crimson (NR8) yellow based

Dinitroaniline Orange (PO5)

Benzamidazolone Orange

Hansa Light Yellow (PY3)

Hansa Yellow (PY3)

Hansa Medium Yellow (PY74)

Benzamidazolone Yellow (PY154)

Indian Yellow (PY100)

Diarylide Yellow (PY83)

Isoindolinone Yellow (PY139)

Azo Yellow
Viridian/Emerald, Hydrated Chrome Green Oxide (PG18)*

Chromium Green Oxide (PG17)*

Ultramarine Light Blue/Green, Red (PB29)*

Ultramarine Violet/Pink (PV15)*

Ultramarine Red*

Quinicridone Red and Violet (PV19)

Quinicridone Magenta (PR122)

Anthraquinone Red (PR177)

Anthroquinone Purple (NR16)

Carbazole Violet/Diaxozine Purple (PV23)

Azo Russet (PBR23)

Azo Dyes

In chemistry, organic compounds are generally any compounds that contain carbon. Most synthetically produced organic compounds are derived from petrochemicals consisting mainly of hydrocarbons. 

Azo dyes are a commercially important family of organic compounds that are widely used to dye textiles, leather and some foods. Azo dyes are very bright and are often used for fluorescent colors.

Many kinds of azo dyes are known. Some classes include disperse dyes, metal-complex dyes, reactive dyes, and direct or substantive dyes. Direct dyes are used for cellulose-based textiles, which includes cotton. These dyes bind to the textile by non-electrostatic forces.

Azo dyes are prepared by the condensation of nitroaromatics with anilines followed by reduction of the resulting azoxy intermediate:

Azo dyes derived from benzidine are carcinogens; exposure to them has been associated with bladder cancer. Accordingly, the production of benzidine azo dye was discontinued in the 1980s in many western countries. Congo Red is one such dye that was also used as a pH indicator and it has an interesting history. 

Congo red was first synthesized in 1883 by Paul Böttiger. He was looking for textile dyes that did not require a mordant step. He filed the patent under his own name and sold it to the AGFA company of Berlin. AGFA marketed the dye under the name "Congo red", a catchy name in Germany at the time of the 1884 Berlin West Africa Conference, an important event in the Colonization of Africa. The dye was a major commercial success. In the following years, for the same reason, other dyes were marketed using the "Congo" name: Congo rubine, Congo corinth, brilliant Congo, Congo orange, Congo brown, and Congo blue. It is no longer available in the United States, but can be obtained from China.

The Pap Stain was developed by George Papanicolaou in 1942. It is used in cytology to help pathologists to make a diagnosis under a microscope. He published five formulas for his stains. Three of them contain Harris’s Hematoxylin which uses potassium alum as a mordant and is oxidized with mercuric oxide. Don’t try this at home. Just order it from a lab.

Haematoxylin is logwood dye. It was first used by the Mayans and Aztecs in Central America. Haematoxylin was used to produce blacks, blues and purples on various textiles. It remained an important industrial dye until the introduction of suitable replacements in the form of synthetic dyes. 

Without a mordant, it produces purple. It produces a blue dye with alum as a mordant. It produces a black dye with copper or chrome as a mordant.

Contemporary usage of haematoxylin includes the dyeing of silk, leather, and sutures.

Haematoxylin has been used as the primary component of writing and drawing inks, although the timing of first use as an ink is unclear. Haematoxylin was added to some iron gall inks, which take time develop to fully darken when applied to paper. In this case the Haematoxylin provided some initial color before the iron gall reached its full depth of color. William Lewis in 1763 is credited with first to use haematoxylin as an additive in iron gal inks. In 1848 Friedlieb Ferdinand Runge produced a heamatoxylin ink that was non-acidic using a potassium chromate as the mordant, which had the advantage of not corroding steel pens. Van Gogh is known to have used haematoxylin ink with a chrome mordant in a number of his drawings and letters.

Another Pap stain is Orange G, aka: Acid Orange 10, CI 16230 which is an azo dye. It is also a pH indicator that shows brilliant orange in neutral and acid pH or red in pH greater than 9.

The third staining solution is composed of three dyes, Eosin Y (Acid Red), Light Green SF yellowish (Acid Green), and Bismarck Brown Y.

The leuco form of malachite green was first prepared by Hermann Fischer in 1877.  Malachite green is traditionally used as a dye. It is also used as an antibacterial for farmed fish in commercial aquaculture. Its absorption into fish tissue has been a cause for concern.

Malachite Green has frequently been used to catch thieves and pilferers. Money is sprinkled with the anhydrous powder. Washing one’s hands after handling the contaminated money will result in a green stain that lasts for several days.

Methyl violet, a dye first synthesized by Charles Lauth in 1861. It was marketed under the name, Violet de Paris and used as a histology stain in 1875. Crystal violet was first synthesized in 1883 by Alfred Kern. He developed Basic Violet 4 CI 42600. In 1880, Georg Grübler mixed the two stains and called his mixture Gentian Violet. It was first used as a stain by Hans Christian Gram in 1884. In 1890, ophthalmologist Jakob Stilling discovered the antiseptic properties of gentian violet. In 1912, John Churchman found that most Gram-positive bacteria were sensitive to the stain, but Gram-negative bacteria were not. Gentian Violet has been used for over 100 years to treat infants for thrush and is an active ingredient in Wound Coat for horses. Like Malachite Green, Crystal Violet is readily absorbed into fish tissue.

The following dyes are safe. Many of them are classified by the FDA as FD&C or D&C dyes. They are used in conjunction with Lake pigments in makeup. Some of them are also pH indicators*.

Carmoisine CI 14720

Amaranth Red #9 CI 16185

D&C Red #17 CI 26100

D&C Red #22 CI 45380

D&C Red #36 (PR4)

Poppy Red Ponceau 4R D&C Red #7  CI 16255

Acid Red Ponceau S*

Acid Red 87, Eosin Y CI 45380*

Acid Orange 10, CI 16230*

D&C Orange #4 CI 15510

D&C Yellow #8 CI 45350

D&C Yellow #11 CI 47000

Quinoline Yellow FD&C Yellow #13 CI 47005

Acid Green, FD&C Green #2 CI 42095*

FD&C Green #3 CI 42053

Green S FD&C Green #4/50 CI 44090*

Malachite D&C Green #5 (PG2, PG4) CI 61570*

D&C Green #6 CI 61565

D&C Green #8 CI 59040

Brilliant Blue, Acid Blue, FD&C #1 CI 42090*

Patent Blue V FD&C Blue #5 CI 42051

D&C Violet #2 CI 60725

D&C Violet #2 EXT CI 60730

D&C Crystal Violet 3 (Methyl Violet 2B) CI 42535

D&C Basic Violet 4, Gentian Violet (Methyl Violet 10B) CI 42600

Acid Fuchsine, Acid Violet #19 CI 42685*

Bismarck Brown Y, Basic Brown #1 CI 21000*

Caramel FD&C Brown #3 CI 20285

Haematoxylin FD&C Black #1 CI 28440*

pH Indicators

A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH (acidity or alkilinity) of the solution can be determined visually. Hence, a pH indicator is a chemical detector for hydrogen ions. Normally, the indicator causes the color of the solution to change depending on the pH.

Litmus, used by alchemists in the Middle Ages and still readily available, is a naturally occurring pH indicator made from the lichen species, Roccella tinctoria, pictured above. The word litmus is literally from 'colored moss' in Old Norse. The term 'litmus test' has become a widely used metaphor for any test that purports to distinguish authoritatively between alternatives.

Many plants or plant parts contain chemicals from the naturally colored anthocyanin family of compounds. They are red in acidic solutions and blue or purple in alkaline. Anthocyanins can be extracted with water or other solvents from a multitude of colored plants or plant parts, including from leaves (red cabbage, dog’s mercury); flowers (butterfly pea, geranium, poppy, or rose petals); berries (turnsole, blueberries, blackcurrant); and stems (rhubarb). 

Hydrangea macrophylla flowers can change color depending on soil acidity. In acid soils, chemical reactions occur in the soil that make aluminum available to these plants, turning the flowers blue. In alkaline soils, these reactions cannot occur and therefore aluminum is not taken up by the plant. As a result, the flowers remain pink.

Plant Based

Beet juice (pictured above) turns from red in acidic solution to yellow in a very alkaline solution, displaying a range of colors in between.

Blackberries, black currants, and black raspberries change from red in an acidic environment to blue or violet in an alkaline environment.

Blueberries are blue around pH 2.8-3.2, but turn red as the solution becomes even more acidic.

Cherries and their juice are red in an acidic solution, but they turn blue to purple in an alkaline solution.

Curry contains the pigment curcumin, which changes from yellow at pH 7.4 to red at pH 8.6. Have fun with your curry dishes by adding baking soda instead of salt.

Delphinium Petals: The anthocyanin, delphinidin changes from bluish-red in an acidic solution to violet-blue in an alkaline solution.

Geranium Petals: Geraniums contain the anthocyanin, pelargonidin, which changes from orange-red in an acidic solution to blue in an alkaline solution.

Grapes: Red and purple grapes contain multiple anthocyanins. Blue grapes contain a monoglucoside of malvidin, which changes from deep red in an acidic solution to violet in an alkaline solution.

Horse Chestnut Leaves: Soak horse chestnut leaves in alcohol to extract the fluorescent dye esculin. Esculin is colorless at pH 1.5 but becomes fluorescent blue at pH 2. Get the best effect by shining a black light on the indicator.

 

Blue Morning Glories: Morning glories contain a pigment known as "heavenly blue anthocyanin," which changes from purplish-red at pH 6.6 to blue at pH 7.7.

Onions are olfactory indicators. You don't smell onions in strongly alkaline solutions. Soak a white or yellow onion in salt water before cutting it and it won’t make you cry. Red onion also changes from pale red in an acidic solution to green in an alkaline solution. Try pickling a red onion in soda water instead of vinegar.

Petunia Petals: The anthocyanin, petunin changes from reddish-purple in an acidic solution to violet in an alkaline solution.

Poison Primrose: Primula sinensis has orange or blue flowers. The orange flowers contain a mixture of pelargonins which turn from orange to blue in an alkaline solution. The blue flowers contain malvin, which turns from red to purple as a solution goes from acidic to alkaline.

Purple Peonies: Peonin changes from reddish-purple or magenta in an acidic solution to deep purple in an alkaline solution.

Red cabbage contains a mixture of pigments used to indicate a wide pH range. It turns from purple in an acidic solution to blue in an alkaline solution.

Rose Petals: The oxonium salt of cyanin turns from red to blue in an alkaline solution.

Turmeric contains a yellow pigment, curcumin, which changes from yellow at pH 7.4 to red at pH 8.6.

Chemical Compounds

Chemical pH indicators are the ones used to test pool and aquarium water. I’m sure many of us are already familiar with some of them. These chemicals are used to make fabric marking pens, cheap watercolor markers, children’s paint, children’s washable markers and color changing lipstick. They are very intense and can be diluted to the point being transparent while maintaining their vibrancy. Ten of them function best in an alcohol solution. Those are used to make alcohol markers. In most cases, the dye retains its base color in pH neutral water or alcohol. If you want to test the quality of your art supplies, use lemon juice or ammonia water and see if they change color.

Water Based

Tropeolin OOO: pH 7.6 = yellow, pH 8.9 = rose-red

Chlorphenol red: pH 5.4 = yellow, pH 6.8 = red

Phenol red: pH 6.4 = yellow, pH 8.0 = red

Nile blue: pH 10.1 = blue, pH 11.1 = red

Alizarine yellow R: pH 10.2 = yellow, pH 12.2 = red (azo dye)

Methyl orange: pH 3.1 = red, pH 4.4 = orange

Methyl orange, screened: pH 0 = red, pH 3.2 = purple-grey (lilac), pH 4.2 = green

Tropeolin O: pH 11.0 = yellow, pH 13.0 = orange-brown

Methyl red: pH 4.4 = red, pH 6.2 = yellow

Thymol Blue: pH 1.2 = red, pH 2.8-8.0 = yellow, pH 9.6 = blue

Tropeolin O0: pH 1.3 = red, pH 3.2 = yellow

p-Ethoxychrysoidine: pH 3.5 = red, pH 5.5 = yellow

Indigo Carmine: pH 11.4 = blue, pH 13.0 = yellow

Malachite Green (PG5): pH 0 = yellow, pH 2.0-11.6 = green, pH 14.0 = colorless (azo dye)

Methyl purple: pH 4.8 = purple, pH 5.4 = green

Bromphenol blue: pH 6.2 = yellow, pH 7.6 = blue

Bromothymol blue: pH 0 = magenta, pH 6.0 = yellow, pH 7.6 = blue

Bromcresol green: pH 4.0 = yellow, pH 5.6 = blue

Tetrabromphenol blue: pH 3.0 = yellow, pH 4.6 = blue

Azolitmin (litmus): pH 4.5 = red, pH 8.3 = blue, replaced Congo Red (azo dye)

Gentian / Methyl Violet: pH 0 = yellow, pH 2.0 = blue-violet (azo dye)

Bromphenol blue: pH 3.0 = yellow, pH 4.6 = blue-violet

Alizarin yellow: pH 10.0 = yellow, pH 12.0 = lilac (azo dye)

Alizarin sodium sulfonate: pH 3.7 = yellow, pH 5.2 = violet

Diazo violet: pH 10.1 = yellow, pH 12.0 = violet (azo dye)

Bromcresol purple: pH 5.2 = yellow, pH 6.8 = purple

Poirrier's blue: pH 11.0 = blue, pH 13.0 = violet-pink

Cresol red: pH 7.2 = yellow, pH 8.8 = plum

Trinitrobenzoic acid: pH 12.0 = colorless, pH 13.4 = orange-red

p-Nitrophenol: pH 5.0 = colorless, pH 7.0 = yellow

Cresolphthalein: pH 8.2 = colorless, pH 9.8 = purple

Alcohol Based

2,4-Dinitrophenol: pH 2.4 = colorless, pH 4.0 = yellow, 50% alcohol

Neutral red: pH 6.8 = red, pH 8.0 = yellow, 70% alcohol

α-Naphthyl red: pH 3.7 = red, pH 5.0 = yellow, 70% alcohol

Nitramine: pH 11.0 = colorless, pH 13.0 = orange-brown, 70% alcohol

α-Naphtholphthalein: pH 7.3 = pale red or pink, pH 8.7 = teal, 70% alcohol

Pentamethoxy red: pH 1.2 = red-violet, pH 2.3 = colorless, 70% alcohol

Phenolphthalein: pH 0 = orange-red, pH 8.3 = colorless, pH 10.0-12.0 = purple-pink, pH 13.0 = colorless, 70% alcohol

Rosolic acid: pH 6.8 = yellow, pH 8.0 = red, 90% alcohol

Salicyl yellow: pH 10.0 = yellow, pH 12.0 = orange-brown, 90% alcohol

Methyl yellow: pH 2.9 = red, pH 4.0 = yellow, 90% alcohol

α-Naphtholbenzein :pH 9.0 = yellow, pH 11.0 = blue, 90% alcohol

Thymolphthalein: pH 0 = red, pH 9.3 = colorless, pH 10.5 = blue, 90% alcohol

Non Staining Colorants

Non-staining colorants are pH indicators or azo dyes that are chosen for their fugitive properties. They are non-staining to skin, most fabrics, and non-porous surfaces when used sparingly. They are used for coloring laundry detergent, bath bombs, pool water, soap, toilet chemicals and lab specimens. They are available in tablet form (Color Splash or Crayola Bath Dropz) for coloring bath water, powder form for coloring pool water or poster paint, and liquid (glycerin) for coloring bath bombs and soap. In this case, they are called soap dyes.

Pick which pigments you want to work with according to their properties. You may not wish to mix a synthetic pigment with a mineral pigment. You must wear a face mask while working with any pigment to prevent inhalation, but also to prevent yourself from sneezing or coughing and blowing the powder to the four winds!