Art Education: Pigments Lesson

Pigment versus Dye

A distinction is usually made between a pigment, which is insoluble in the vehicle (resulting in a suspension), and a dye, which either is itself a liquid, or is soluble in its vehicle (resulting in a solution).  A pigment can be manufactured from a dye by precipitating a soluble dye with a metallic salt.  The resulting pigment is called a lake.  The exceptions are vat dyes, which are insoluble, unless mixed in a specific oxygen free solution.  In insoluble suspension they act as a pigment.

History & Hue

The first pigments were made from natural organic minerals, plants, insects, shellfish and soot.  Few of these are used today, but their replacements names still designate their original color.  By convention, a contemporary mixture of pigments that replaces an historical pigment is indicated by calling it a hue, but manufacturers do not always follow this designation.  The Color Index International (CII) is now the standard for identifying pigments.  It encompasses more than 27,000 products under more than 13,000 generic color index names.  Lightfast ratings are by the American Society of Testing and Materials (ASTM). Artists should only use colors rated I or II.

Let there be Light(fast)

Lightfastness I: Excellent – These samples are exposed to an accelerated dose of light energy equivalent to 100 years of museum-lit conditions.  When comparing an exposed and unexposed sample, when held adjacent, would reveal at worst, a barely perceptible color change.

Lightfastness II: Very Good – Under the same conditions, a visual comparison of adjacent unexposed and exposed samples would reveal a perceptible color change.  This change would quickly become imperceptible as the sample pieces are moved apart (organic pigment fade, inorganic pigments darken).

Pure Pigment

Paint with the marketing name cobalt blue should contain only one pigment ingredient: cobalt blue (PB28). This is the preferable formulation for artist’s paints. You can directly see the quality (color, saturation, and tinting strength) of the pigment, and the lightfastness of the paint is as good as it gets. Some manufacturers tout that most of their colors are single pigment formulas.  Pigments achieve color by absorbing the majority of the light spectrum, except the color reflected to the viewer.  When multiple pigments are used to achieve a color, the reflective purity of each pigment color experiences reflective interference and the resulting color is muted or muddied.

Filler Factor

The second factor to consider is the ratio of pigment to the vehicle and additives.  Some manufacturers heavily dilute the pigment with fillers to reduce their cost.  This is easily tested by mixing the pure color from different manufacturers with titanium white pigment.  In comparison, the paint which remains the brightest after mixing has the greatest strength of color.  One kilogram of cobalt violet deep pigment costs approximately $630.00.  Some manufacturers cut expensive pigments heavily with barium sulphate or aluminum hydrate, which only cost around $0.75 per kilogram. Generally speaking, the finer the pigment is ground, the more brilliant the color.

Oil Variations

As far as the oil vehicle is concerned there is still some debate.  The strongest bonding and most fleible oil is linseed oil made from flax seeds and the best  linseed oil from the first pressing (virgin), containing the maximum acids, which have good oxidizing and polymerizing effect on the painting. Paint manufacturers use safflower oil, poppy oil, or walnut for whites and lighter colors as they do not yellow, but they are slower drying and not as strong a bond and can crack more than linseed oil in heavy application. Often paint manufactures use a mixture of oil mediums.

Time and Toxicity

Artists who sell their painting should be confident that it will stand up to the ravages of time. With the new pigments available there is little need to use historically fugitive or highly toxic pigments.  Mixing antiquated pigments resulted in many negative side effects; for example, chromium pigments and copper pigments would darken over time when mixed with sulfur pigments. Lead compounds darkened when mixed with cadmium pigments.  This is why many old paintings appear dark and foreboding.  Today there is no need to use chromium, mercury, lead or any of these highly toxic pigments.  Perhaps the most damaging element to lightfastness, historically, has been badly made pigments containing free sulfur, which would slowly darken other colors.  Top quality paint manufacturers bind the sulfur so that it doesn’t react with other pigments. As most artists already know, cheap paint yields cheap results.  Oil paint tends to become more transparent in time, so the artist should always paint from light to dark. Varnishing oil paintings when dry is still recommended to protect pigments from moisture and chemicals in the air after the oil paint has totally cured.

Today’s pigments are either non-toxic or have a very low toxicity rating. Unless vast quantities of paint are eaten there is little cause to worry; however, artists should still avoid inhaling pigment powder.  There was one known case where an imprisoned artist saved enough emerald green (arsenic) paint over a period of time to poison himself.  There is a rumor, however, that for a lark, Napoleon’s Irish guards on the isle of St. Helena painted him emerald green to celebrate St. Patrick’s Day, resulting in his death from arsenic poisoning.

Thanks to…

I have included a cross section listing of artist pigments and their formulation taken from Ralph Mayer’s “The Artists Handbook”.  I also borrowed heavily on the pigment descriptions from “Handprint” by Bruce MacEvoy and several other articles published on the internet.  As I don’t plan to publish this for profit, I won’t list every source.  That way you may think some of this came from my own vast store of knowledge.