PIGMENTS

IN THE SEVERAL thousands of years of  art  history  there  are  three major technological advances that have changed painting and drawing for all time. The first  major  technological  development  occurred when metal tools were developed during the latter part of the Bronze Age (1500 to 1000 B.c.) and minerals in rock form could for the first time  be  easily  processed  into   pigments.   Before   this   time   an   artist's palette consisted of several  shades of  brown and  brownish  yellows, as well as black and white. The Bronze  Age brought  with  it a deep red (cinnabar), a bright orange-red (realgar), a brilliant yellow (orpiment), a deep blue (lapis lazuli), a pale blue (azurite), and a green (malachite). The transition in painting must have been like the later transi­ tion from black-and-white to color photography.

The next major development did not occur until  the age of industrialization in the nineteenth century, when the technology to synthesize mineral salts was developed. Almost all of the mineral pigments used today  were  developed between 1800 and 1910. Aureolin, chrome yellow, lemon yellow, zinc yellow, cadmium orange, cadmium yellow, cadmium red, alizarin crimson, chrome red, chrome green, chromium oxide green, cobalt green,  emerald  green,  viridian, cobalt blue, synthetic ultramarine, and cobalt violet  were  all introduced  during this period. These new pigments allowed the creation of  paintings  that  could never before have been produced. Without the development of these pigments it would be safe to assume that the Impressionist, Luminist, or Expressionist movements could not have occurred.

The last major transition is happening right now with the development of new synthetic organic pigments, which have broadened the  artist's  palette  beyond  most painters' abilities to cope. There are so  many  potential  new  colors  that  most manufacturers are unable to make them all available. For every phthalo­ cyanine, azo, anthraquinone, quinacridone, indanthrone, and dioxazine pigment now in use as an artists' pigment, there are at least five others that could be.

 

This vast spectum has taken issues like the  nature  and  use of color, as well  as  the nature of perception, from academic speculations to practical concerns. Painters tend to see pigments as colors rather than as chemicals. Pigments are, however, chemicals that possess  many  characteristics in addition  to their  ability to absorb light and reflect a particular color of the spectrum.  The  painter  must take these chemical characteristics into consideration to avoid such disastrous results as the cracking of paint films, the fading of colors,  and serious  injury  to  his or her health. This section includes all the  latest  information  available  on more than one hundred of today's most significant colors, their pigment compo­ sition, and their chemical properties, with emphasis on practical information, including pigment compatibility, permanence, and toxicity.

A pigment by itself is of little use. Dry pigments have no inherent adhesive quality. To be kept in place, pigments must be mixed with some type of binder. Attempts have been made to rub dry pigments into textured surfaces,  but  the results are often of poor quality and cannot be considered durable. Although this might seem fairly obvious, many established artists have attempted to sprinkle pigment on surfaces, or to use a water-soaked brush to apply dry pigments.

Over the centuries, several successful methods of mixing a binder with a pig­ ment have been developed. The pastel is an example of a dry  mixture.  To pro­ duce a soft pastel, pigments are mixed with water and a gum binder  and  then dried. Because there is so little binder,  soft  pastels are  not durable  and  have  to be used on textured surfaces. Soft pastel drawings are delicate and easily dis­ turbed; therefore, they require extensive protection and  must  be  stored  and framed in specific ways. (See Framing and Storage,  pages  275  to  307.)  Oil pastels and colored pencils are more durable and can be applied to smoother surfaces because their binder is wax. The most popular method of  making  a  pliable mixture of pigment and binder is the making  of  paint.  Paint is produced  by grinding or mixing a pigment with a medium  such  as  linseed  oil  for  oil paints, or a water solution of gum resins for watercolor.

When a binder and pigment are mixed together, this is called a medium. For example, if linseed  oil were used  as the binder,  the medium  would  be oil paint;  if an egg binder were  used,  the medium  would  be egg tempera.  Pigments take  on various characteristics depending on the particular binder.

 

 

CHARACTERISTICS OF PIGMENTS 

ALL OF us see the labeling on our packaged foods. Some of us actually read the labels, but how many of us know  what  any of  it  means  or how  to  translate  it into useful information? The same is true of artists'  materials.  This  section explains the essential nature of pigments and provides a working knowledge  of their characteristics to help you to distinguish one pigment from  another  so that you may use them to your best advantage.

 

NAMES OF PIGMENTS

The names used for various pigments often make about as little  sense  as  the names that automobiles are assigned by their manufacturers, and frequently con­ vey even less information. This is because several methods are used to name pigments and, even after several thousand years, one  is  no  less  confusing  or more efficient than another.

Pigments used before the nineteenth century were most often named after their discoverer, the location of their source, their appearance,  or just  poetically. Due to advances in technology at the tum of the nineteenth century, new synthetic mineral pigments were being rapidly discovered. Many of these pigments were given names that included part of their chemical  names-cobalt  blue and  cad­ mium yellow, for example. New pigments, whose exact chemical nature was not known, continued to be referred to by the names that had  been used  in the past. As confusing as the names were at this time, they did relate to  a  specific pigment or group of pigments. This did not last for long and things got much worse. With the development of new pigments from the end of the nineteenth century until today, it has been found that many of these new pigments have characteristics that allow them to be used as substitutes for  older,  less  perma­ nent, or more costly pigments. Many manufacturers simply substituted the newer pigment for the old one, and kept the old name. Since this was not a coordinated effort among manufacturers, not everyone made the same substitutions. There­ fore, today, it is easily possible  for a  pigment  to have several  names,  or a color to have several pigments. If the name on the container is not what is inside, then information about such characteristics as permanency, compatibility, and trans­

parency cannot be relied upon.

'

Some manufacturers are attempting to clarify this confusion by adding  the names and numbers assigned to specific pigments by the Society of Dyers and Colourists of London  to the common  name on the label.  (The same  information is available from the American Association of Textile Chemists and Colorists, P.O. Box 12215, Research Triangle Park, NC 27709.)

In the Table of Pigments and Colors, I have included these Colour Index (C. I.) names and numbers. It  is  important,  however,  to  under­ stand what the C. I. names and numbers do not indicate-such characteristics as purity, quality, and  concentration-nor  do  they  distinguish  among  the  shades  that may exist within a specific pigment. Phthalocyanine blue, for example, has several shades that range from a reddish-blue to a greenish-blue, although  all shades have the same C. I. name and number. Phthalocyanine blue is, with rare exception, contaminated with the carcinogen PCB and is always mixed with an extender when used as a paint,  yet none  of  this information  would  be reflected by the names and numbers.

C. I. names and numbers can be  helpful,  occasionally,  in  comparing  the quality of different brands of paint. Cadmium red paint,  for  example,  can  be made from either chemically pure (C. P.) or chemically concentrated (C. C.) cadmium sulfo-selenide. C. P. cadmium sulfo-selenide is assigned  the C. I.  name of Pigment Red 108 and the C. I. number of 77196, and C. C. cadmium sulfo­ selenide, which is extended with barium sulfate up to a concentration of  15 percent, is assigned the same C. I. name, but a different C. I. number, 77202. Cadmium sulfo-selenide is among the most costly of pigments and is therefore often the first to be compromised in the manufacture of  paint. The finest  paints  are made with the purer and more costly Pigment Red 108, C. I. 77196.

 

PERMANENCE

Permanence is defined as continued existence. All existence is conditional or relative. Nothing is truly permanent. A substance may only be considered per­ manent because it has a longer continuity of existence  than  another  substance. The only thing that does seem to be permanent is impermanence. A common metaphor for permanence is, "It's set in concrete," but even concrete has been recently found to be good for only a hundred years before it becomes brittle and begins to crumble.

It is commonly believed that the finest quality of pigment is synonymous with the highest degree of permanence. This is not the case.  In fact,  the oldest  and  most reputable companies attempt to offer the widest possible range of colors, which includes those that are both modern and traditional. Consequently,  there  will be a wide range of permanency in  a  given  manufacturer's  selection  of colors.

There  are  many  factors  that  influence   the  permanence   of  pigments.  These include weather, ozone, visible light, ultraviolet light, acid, alkali, water, oil, solvents, detergents, humidity, air pollutants, temperature, the type of  medium used, the ground on which the pigment is applied, and whether it is mixed with other pigments. Despite all the technical advances and fancy equipment for the testing of  permanency,  the method  is still basically  the same-trial  and  error  and the examination of past artwork. Technical advances have only developed the limited accelerated-aging testing procedures.

Accelerated aging tests are heavily based on theory and speculation.  In addi­ tion, there is no standardization of testing procedures among anufacturers of pigments and paints. Tests can range from the very harsh, involving exposure of pigments, or paints, to direct sunlight outdoors, or a more moderate testing pro­ cedure proposed by the American Society  for Testing  and  Materials  (ASTM) in D 4303-83, Standard Test Methods for Lightfastness of Pigments Used in Artists' Paints. The ASTM guidelines are for lightfastness testing only. They recommend using one of three types of  light-sunlight, daylight  fluorescent  light,  or  xenon­ arc light that is filtered through glass indoors.

Permanency ratings for pigments that have  been  in  use for seventy-five  years or more can be safely relied upon because they have been proven under actual conditions. Ratings on pigments in use for less than seventy-five years, and espe­ cially for less than twenty-five years, have to be viewed with some suspicion. Pigments tested through accelerated aging rarely include more than three  vari­ ables and cannot duplicate actual conditions. Although such testing has  often proven reliable, there have been exceptions. The vast number  of  variables  involved in the natural aging process makes it impossible  to guarantee  the rela­ tive permanency of a pigment. Consequently, any rating given should be consid­ered only as a summation of the best available data and not as a warranty.

When a pigment or paint is exposed to light and a change is measured, the change is then translated in a scale. The Wool Scale is a common international method of rating the lightfastness of a color or a pigment. With the help of some manufacturers I have attempted further to translate this scale, which ranges from 10 to I, into practical terms for the painter.

10: Theoretically, absolutely lightfast

9: Has shown in practice, or theoretically  will  show,  no  observable change .for two thousand years

8: No visible change for two hundred years in its pure form under normal museum conditions

7: No visible change for seventy-five years in its pure form under normal museum conditions

6: No visible change for twenty-five years in its pure form under normal museum conditions

Less than 6 is not considered acceptable for fine or professional  art­ work and is classed as fugitive

The ASTM has proposed the following rating system, which is based on their suggested testing procedures for the determination of the lightfastness of  pig­ ments in oil or acrylic. Manufacturers and researchers who have conformed  to  these guidelines have assigned each color in question to one of three categories:

 

Category I: Excellent lightfastness. Very slight to no color change after the equivalent of one hundred years of indoor museum exposure.

Category II: Very good lightfastness. Less permanent than Category I, but satis­ factory for most indoor painting.

Category Ill: Borderline. Use with caution.

Manufacturers of paint who are not using the ASTM guidelines have condensed scales like the Wool Scale down to four or five categories and then assigned each category a symbol such as a letter or a star. Most manufacturers have been reluctant to make public the correlation of their categories to actual time, such as years, under museum conditions. Since there are  so  many  variables  involved with longevity, no manufacturer could possibly supply a warranty, and it was feared that making such a correlation would imply such a warranty.  Talens was the first company I could persuade to break the ice for the benefit of all painters. Although the actual boundaries drawn between the different  permanency groups, due to the variations in testing procedures, can vary significantly from manufacturer to manufacturer, the highest rating given to a paint by manufactur­ers is most often equivalent to 8 on  the  Wool  Scale.  The  lowest rating,  other than fugitive, is equivalent to 6 on the Wool Scale. In other words, if a manufacturer's  highest rating  is  or  AA,  the color should  show  no visible  change in its pure state under normal museum conditions  for at least  two hundred  years. A color assigned the lowest rating, such as one star or B,  should  show  no  visible change  for  at  least  twenty-five  years  in  its  pure  state  under  normal   museum conditions. (This rating is considered the minimal acceptable limit for an artists' material.) Colors labeled as "fugitive" or that have no rating, will show a visible change within twenty-five years. Although the Talens Company said that its mid­ dle category  ** is roughly equivalent  to seventy-five years under normal museum conditions, there is too much variation among manufacturers to generalize about  the ratings used between the highest and lowest.

This information applies only to artists' paints and not to any other  materials such as graphic arts materials, industrial paints, or house paints,  for  which  the term "permanency" means fifteen to twenty-five years, or one generation.

Despite the enormous spectrum of available artists' colors, a number of paint­  ers have experimented with pigments that do not meet minimum permanency standards (at least 6 on a Wool Scale), such as fluorescents, enamels, even vege­ table juices. Artwork produced with these materials must be considered "self­ destruct" artwork. As long as the customer who collects such a piece of artwork understands its nature, it seems reasonable to produce and sell it. However, there have been several situations where an artist did not do his or her homework and unknowingly produced and sold a  piece  of  "self-destruct"  artwork.  Most  of these situations have been resolved by the artist exchanging the artwork for  another. It would be wise for any professional artist to consider that there have  been successful legal actions taken against the artists and galleries in such cases.

 

 

COMPATIBILITY OF PIGMENTS

Pigments, which are chemicals, can react with one another to form new chem­  icals. When this occurs in artwork the results, such as changes in a painting's appearance, are often undesirable. Chemical reactions can be avoided by not using incompatible pigments or by treating the pigments so that  they  can  be  mixed together without reacting. The only proven treatment  that  will  prevent  most incompatible pigments from reacting  with one another  is to grind  them  into a drying oil, such as linseed oil, which will coat each pigment particle. If all the pigment particles are coated they will not be able to come into contact with one another and react. This is the reason that the greatest variety of pigments  and  colors is found among oil paints.

LeFranc & Bourgeois has supplied additional  permanency  information  on  its oil paint tubes in regard to compatibility. Paints that can be mixed without sig­ nificant reduction in permanency have a large red M painted on the front of the tube.

Compatibility of pigments within oil paints is of little concern if the protective  oil coating is not stripped away. However, if an oil paint is mixed with only a thinner instead of a medium, the thinner will wash away the protective  coating. (For the proper method of thinning oil paints, see page 259.) Since most of the chemical reactions in this case are slow, it may be  several years  before  the  effects of this misuse become obvious. Unfortunately, the excessive use of thin­ ners has become a common method of painting.

In watercolors, acrylics, and soft pastels, the binder does not isolate and pre­  vent potentially incompatible pigments from coming into direct contact and react­ ing with one another. Consequently, such  pigments are,  in  many cases,  left QUt of the manufacturers' range of colors  when  producing  these media.  This cannot be totally relied upon, and some basic knowledge of the most common incom­ patible mixtures is necessary.

The incompatibility of unprotected pigments containing sulfur and unprotected pigments containing lead is well known. For example, lead white, chrome red, chrome green, and Naples yellow should never be mixed with cadmium red, cadmium yellow, cadmium orange, cadmium green, vermilion, or  ultramarine blue. When unprotected, these mixtures will tend to blacken. Another less com­ mon example is the incompatibility between unprotected pigments containing sulfur and some unprotected pigments containing copper, such as emerald green, malachite, verdigris, and azurite. Since  only  emerald  green  is still  available  as an artists' pigment, there is little concern here.

There is another type of incompatibility that  is  not  well  understood. It  has been known for some time that the mixing of any color, particularly organic dye-pigments (for example, alizarin crimson and cadmium red hue),  with  white can result in either a bleaching effect to the color  or  a  staining  effect· to  the white. This gave little cause for concern in the past because there were so few organic dye-pigments available. Today, more than half of the commercially available dyes and pigments are organic dye-pigments, and as more of these dye­ pigments have been added to artists' color lines so has there been an increase in reports of bleaching and staining. Until more is known, it might be wise to be conservative about using mixtures of organic dye-pigments and white.

Although it is rare, dilute watercolors and very dilute acrylics can suffer from incompatibility due to electrochemical properties.  Cobalt  blue,  for  example, when mixed with burnt sienna will form aggregates that settle to the bottom resulting in a gritty paint mixture.

TOXICITY

Indiscriminate application of powdered pigments to artwork  or  the  manufacture of homemade paint without proper protection is simply suicidal. All pigments, particularly in their dry, powdered form, should be regarded as hazardous or potentially hazardous. Most of us would not live near a factory  that  produces many of the chemicals used as pigments, or a dump  where these  were  disposed of, yet we take these same chemicals  into  our  studios  or,  worse,  our  homes, with few or no safeguards.

The degree to which a pigment is toxic varies with the type of exposure. A pigment may be relatively nontoxic when exposed to the skin, moderately toxic when ingested, and highly toxic when inhaled. Virtually all pigments have their highest toxicity rating when either ingested and/or inhaled. The use of such  solvents as turpentine, which can be absorbed through the skin, can carry pig­ ments through the skin that would not otherwise pass.  In the Table of  Pigments and Colors (pages 166 to 199), the highest toxicity rating given to a pigment has been used, regardless  of  the type of  exposure.  The toxicity  rating also attempts to take into account the contamination  of  a  pigment  by  hazardous  material. Many pigments have forms in which they  are less easily absorbed  by the  body and are, consequently, less hazardous, but it is unwise to rely on  the  possibility that the pigment in use is of the safer variety. It is wise to treat all pigments as hazardous or potentially hazardous. The following guidelines, which  are used in the Table of Pigments and Colors, are for single exposures and are relative to the sensitivity of the individual. Carcinogens are labeled separately  and allergies are not covered.

Highly toxic means that serious injury or death will result from absorption of a small amount, such as a mouthful, by a healthy adult.

Moderately toxic means that temporary to permanent minor injury  will result from absorption of a small to moderate amount by a healthy adult.

Slightly toxic means that temporary minor injury will result from absorption of a small to moderate amount by a healthy adult. Larger quantities  could  cause  greater damage.  Nontoxic means that no detectable injury will occur from absorption of small to moderate amounts by a healthy adult. Nontoxic does not mean safe or nonhazardous.

PURITY

The purity of a pigment can vary greatly. The average level of purity is the industrial grade, which is not chemically pure. The next grade is the "chemically pure" pigments,  in  which some trace levels of  contaminates  up to approximately 1 percent can still be found. The next level of purity is the grade used by the cosmetic and pharmaceutical industries. Most of the pigment that is readily available in bulk is of the industrial grade. For most industrial purposes, however, and for most amateur-grade paints, this grade would be considered ade­ quately pure. In making the finest grades of artists' paint,  chemically  pure pigments are preferred. Levels of purity above this in artists' paint  is  unwar­ ranted in all concerns, except where toxicity is involved.

Only the experienced can differentiate between these levels of purity. If you make small-scale paintings that will be viewed from close  up, or use watercolors or egg tempera, or are involved with restoration, purity may be important. If you work very large or on murals, small impurities will not be as noticeable  if  you have to stand back twenty to thirty feet to see the whole artwork.

 

TYPES OF PIGMENTS

 

THE OLDER, more traditional pigments were derived mostly from substances that existed naturally in the environment. Even when some of them were later syn­ thesized, they were not chemically altered. These older pigments produce colors that can be seen in nature and tend to convey a sense of naturalness, even when used for abstract works.

The new, synthetic pigments are still derived from such natural substances as petroleum, but they have been chemically modified  to create  a  new  substance that is unnatural to the environment and, to many, has an unnatural appearance. Many of these colors, because of  their industrial  applil:ations, are  now  part  of our cities' visual environment, our synthetic environment.

In this comparison between modern and traditional pigments there is no sug­gestion that the natural pigments are better than the synthetic ones. The char­acteristics of both types of pigments can be exploited to a painter's advantage to accomplish a particular effect.

I have grouped pigments in regard to whether they are  inorganic  or organic,  and whether they have been synthesized.  Organic  pigments  are either composed of carbon or are part of, or produced by, a living organism, such as ivory black (carbon). Natural extracts from animal or plant matter, or synthesized material originating from organic matter, such as petroleum products,  have  been  the  source of many organic pigments.

Inorganic pigments are pigments that do not have hydrocarbons (a molecular arrangement of carbon and water), such as cadmium sulfide (cadmium red), but include oxides and sulfides of carbon, like copper carbonate (malachite green, genuine). Inorganic pigments are either natural salts and  minerals  extracted directly from the earth or rocks or are synthesized from salts and minerals.

 

NATURAL INORGANIC PIGMENTS

Natural inorganic pigments are found in nature as minerals or earth and are then ground, sifted, washed, and sometimes cooked (calcinated). The tem1 "natural mineral pigment" is used to describe  natural  inorganic  pigments  that  are found as naturally occurring metallic salts, such as basic copper carbonate (azurite and malachite). The terms "earth color" and "earth pigment" are used to describe natural inorganic pigments that, in addition to being naturally occurring metallic salts, have significant quantities of clay and/or silica naturally mixed into them, such as hydrated ferric oxide and silica (raw sienna).

 

SYNTHETIC INORGANIC PIGMENTS

Almost all of the inorganic mineral pigments used today are manufactured, or synthetic. A synthetic version of a pigment may be chemically identical to the natural form, but it is produced artificially  rather than  naturally.  It may also  be  an entirely new pigment created from minerals.

An example of a naturally occurring inorganic mineral pigment would be gen­ uine ultramarine blue, which is derived from the gemstone lapis lazuli. Synthetic ultramarine blue, on the other hand, is made by a modem process that combines silica, alumina, soda, and sulfur, the basic elements of  the  naturally  occurring lapis lazuli. Although, chemically, they are almost  identical,  lapis  has  a crystalline structure, which gives greater depth and beauty than the synthetic pigment.

One example of an entirely new  synthetic  mineral  pigment  is  cadmium yellow, which was invented in 1817. Cadmium was mined from  the  earth  and then extracted by turning it into a man-made salt that could then be used as a pigment.

Glass pigments are synthetic inorganic pigments in an unusual package. The pigment Egyptian blue, in use from 1500 B.C. to 500 A.D., was made from small glass  particles  called  frit,  which  were  ground   to   make   the   pigment.   The   exact color made from this pigment depended upon the size of the particles of glass. When the glass frit was ground to a small particle, it was a pale blue. A coarser grind produced a bright blue. This method of making color is still used in Japan and the name given to these pigments is "new earth." The Japanese have elabo­ rated on this method of using the size of the glass particles to help determine a color and have taken ten to fifteen base colors and ground them into ten to fifteen different sizes, resulting in a palette of more than one hundred colors

SYNTHETIC ORGANIC PIGMENTS

There are currently about seven thousand organic dyes synthesized from coal tar and petrochemicals, to which approximately two hundred more are added  each year. A dye, as opposed to a pigment, is soluble in the medium in which it is applied, thus making it impractical to make paint directly from a dye. For exam­ ple, if a dye is mixed directly into linseed oil it would readily dissolve into it. However, when this mixture is mixed with other paints, applied to a painting ground, or used with a brush, it would  dissolve  into them  just as readily,  stain­ ing and bleeding uncontrollably. To regain control  it  is  necessary  to convert  a dye into a pigment, which  is insoluble  in  the  medium.  This is done chemically  by attaching the dye to an insoluble, inert substrate, such as aluminum hydrate. (This is like dyeing cotton threads  before weaving  them into a fabric.) The result  is called a dye-pigment, also known as a lake. After the dye is attached  to something solid and insoluble, it can be formed into a paint just like any other pigment. (However,  just as dyed fabric is tested to be colorfast, so must a dye-pigment be found to be bleed-resistant). The synthetic organic pigments used in paints are "dye-pigments."

Because many of these new pigments were less costly, and because there have been dramatic improvements on the range of available  colors,  many  of  them were made available before rigorous testing for bleeding was  performed.  For those painters for whom bleeding of one color  into  another,  no matter how slight, is a problem, a simple, but not conclusive, bleed test can be performed.

A watercolor or gouache can  be tested  by first applying  a dilute  watercolor  to a hot-press watercolor paper and left to dry. Then, using either  a  sponge  or a large, soft, wash brush, attempt to wash away the watercolor. Most nonbleeding pigments will be almost totally removed. Pigments that tend to bleed will leave a significant stain.

Oil colors can be tested by applying a thin coat of white paint over a semidry and a dry layer of the test color. Fast bleeders will tint  the  white  overpaint whether wet or dry, within one day. Slow bleeders will show color in the  white with the semidry test color.

There are three major groups of synthetic organic pigments used in artists' paints-anthraquinone, azo, and phthalocyanine. The first, anthraquinone, was 1,2-dihydroxyanthraquinone (alizarin crimson) developed  in  1868  in an  attempt to understand the coloring properties of madder root. This discovery led to the development of several indanthrones, of which one has come into  use  among artists as indanthrone blue.

The second group, azo, refers to a particular molecular arrangement among nitrogen-containing organic molecules. Although azo dyes were  developed  as early as 1880, it was the development of naphthol AS (naphthol red) in 1912 that heralded the birth of stable dye-pigments, which today include arylides (used to make hansa yellow, cadmium yellow hue), perinones (perinone orange), and naphthols (naphthol red, naphthol crimson, and cadmium red hue).

The third major group is the phthalocyanine dyes (phthalocyanine blue and green). Phthalocyanine was first discovered in 1907. It was rediscovered several times after that until the 1930s, when  it  was developed  for artists'  use.  Out  of this group came the quinacridones, of which gamma-quinacridone (quinacridone magenta) and quinacridone violet b (quinacridone violet) have become relatively commonplace.

 

NATURAL ORGANIC PIGMENTS

Natural organic pigments include dyes that were converted into dye-pigments (lakes) and pigments made from either animal or plant sources. All plant-source pigments, such as madder, indigo, and gamboge, are dye-pigments. Animal or plant-source pigments are all dye-pigments with the one  exception  of  carbon from bone. Examples of animal dye-pigments are sepia and Indian yellow. 

 
Pigments and Colors

VARIOUS CHARACTERISTICS of pigments and colors are explained in the table that follows. Below is a definition of terms as they apply to this table.

 

Common Name

The common name is the name most commonly used to describe  a  particular  color or pigment. The Colour Index Name and  the  Colour  Index  Number  are used in conjunction with the common name to be as specific  as  possible  in naming pigments. The Colour Index Names and Numbers do not in any way indicate purity, quality, or concentration, or distinguish between the shades that may exist within a specific pigment. Phthalocyanine blue, for example,  has sev­ eral shades that range from a reddish-blue to a greenish-blue, yet all shades have  the same Colour Index Name and Number. Phthalocynine blue is, with rare exception, contaminated with the carcinogen PCB and is always mixed with an extender when used as a paint; yet none of this information is reflected by the names and numbers. Another example is cadmium red (cadmium sulfo-selenide), which, with the exception of a few of the finest  paint  manufacturers,  is mixed with the extender barium sulfate; however, the Colour Index  Name and  Number do not change until the percentage of barium sulfate exceeds 15 percent.

Alternate Name

Alternate names include some of the more common European names for the pigment, as well as distinctions made for the various shades,  such  as  light, middle, and deep. Not only can one pigment have several names, but  that one name is often used for more than one pigment.

General Appearance

The word "general" cannot be emphasized too strongly. A pigment's appearance can vary greatly because of its chemical  derivation,  its method of  manufacture,  or the refining process.

Date Introduced

The dates given are those that best  reflect  the  first general  use,  or introduction, of a pigment. The use of the term "recently"  means that the pigment  has come  into use within the last twenty to thirty years and is still in the process  of  becoming established: 

Compatibility with Other Pigments

Some pigments can react chemically  with other pigments  and  their  permanency is thereby affected.

Compatible Media

All media means oil, watercolor, acrylic, and egg tempera. Pigments that signifi­cantly speed up or slow down the drying times of oil media are indicated, as are pigments that add to the flexibility or brittleness of oil paint films.

Source of Pigment

All pigments that are man-made, whether they  are of mineral or organic nature,  are referred to as synthetic.

Chemical Composition

The exact chemical composition of the  pure or the traditional  form of  a pigment is given whenever possible; exceptions are trade secrets or cases where the exact chemical composition is simply unknown.

Relative Toxicity

The degree to which a pigment is toxic varies with the type of  exposure.  A pigment may be relatively nontoxic when exposed to the skin, moderately toxic when ingested, and highly toxic when inhaled. Virtually all pigments have their highest toxicity rating when either  ingested  or inhaled,  or both.  The chart  uses the highest rating given to a pigment regardless of the type of exposure.  The toxicity rating also attempts to take into account the contamination of a pigment with hazardous material. Many pigments have forms  in  which  they  are  less easily absorbed by the body and are therefore less  hazardous;  however,  relying  on the possibility that the pigment in use is of the safer  variety is unwise.  It is  wise to treat all pigments as hazardous or potentially hazardous. The following guidelines are for single exposures and are relative to the sensitivity of the indi­ vidual. Carcinogens are labeled separately and allergies are not covered.

Highly toxic means  that serious  injury  or death  will result from absorption  of  a small amount, such as a mouthful, by a healthy adult.

Moderately toxic means that temporary to permanent minor injury will result from absorption of a small to moderate amount by a healthy adult.

Slightly toxic means that temporary  minor injury will result from absorption  of  a small to moderate amount by a healthy adult. Larger quantities could cause greater damage.

Nontoxic means that no detectable injury will occur from absorption of small to moderate amounts by a healthy adult. Nontoxic does not mean safe or non­ hazardous.

Permanence

There are many factors that influence the pem1anence of pigments. These include weather, ozone, visible light, ultraviolet light, acid, alkali, water, oil, solvents, detergents, humidity, air pollutants, temperature, the type of medium used, the ground on which the pigment is applied, and whether a pigment is mixed with  other pigments. Testing of permanency is still based heavily on theory and spec­ ulation. Only recently have serious attempts been made to use a scientific approach. Permanency ratings for pigments that have been in use for seventy-five  to one hundred years can be safely relied upon because they have proven their ratings under actual conditions. Ratings on pigments in use less than seventy-five years, and especially less than twenty-five years, have to be viewed with some suspicion. Such pigments are tested through accelerated aging tests, which rarely include more than three variables and cannot  duplicate  actual  conditions. Although such testing has often proven reliable, there have been notable excep­ tions. The vast number of variables prohibits any guarantee as to the relative permanency of a pigment, and therefore the information supplied  in this category  is a summation of the best available data and is not intended as a warranty.

Although this category occasionally refers to some other variables, it is pri­marily concerned with lightfastness (the pigment to retain its original color). The Wool Scale, a common international method of rating the light­ fastness of a color or a pigment, is given The American Society for Testing and Materials (ASTM) has proposed new testing procedures for the purpose of rating the lightfastness of  pigments  in oil  and acrylic. Manufacturers and researchers who have followed these guidelines have assigned the ratings that appear in the chart. Three categories are used.

Category I: Excellent lightfastness. Very slight to no color change after the equivalent of one hundred years of indoor museum exposure.

Category II: Very good lightfastness. Less permanent than Category I, but satisfactory for most indoor painting.

Category Ill: Horderline-use with caution

..

Transparency

The degree of transparency or opacity of a pigment can vary with the  medium that is used with the pigment. When a commercial paint is made, fillers are often added, which can greatly alter the transparency depending on the type of filler.  The difference between napthol crimson, for example, and one variety of  cad­ mium red hue is the filler mixed with  napthol  carbamide to make  it opaque like the cadmiums.

Tinting Strength

Tinting strength depends on the quality and purity of the pigment, and may vary accordingly.

 
The Chart Below is not searchable because the text is a picture of each page from my book.

 

The contents of this site were previously published in "ART HARDWARE" by Steven Saitzyk 1987, © COPYRIGHT 

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