Learn the Characteristics of Pigments

This article appeared in the May 2009 issue of The Artist’s Magazine, which is available for order as a digital download. Click here to learn more.

Know Your Pigments

Boost your confidence by learning the characteristics of pigments in your palette.

By Koo Schadler

In Love Conquers All (egg tempera with oil glazes, 6¼x5¼), I originally used a light brown for the stone base on which the bird’s pedestal stands; however, as the painting neared completion, I felt the piece needed more color, so I glazed thin layers of transparent viridian over the faux stonework. Viridian is a strong color—powerfully tinting—so in just three passes, I was able to transform the brown stone ledge to a green one.

Paint, whether used to cover a house, an automobile or a canvas, derives its color from powdered pigments, each with its unique set of attributes. The medium I work in—traditional, pure egg tempera—must be made from scratch. Because of this, I work on a daily basis with powdered pigments, an experience that has given me a wonderful familiarity with their different characteristics.

I know, for example, that when I want a transparent green, I should reach for viridian instead of chromium oxide. I understand why, in water-based media, some pigments float and may need a wetting agent while others sink like a stone. I’ve found that the more I learn about pigments, the more I enjoy painting and the more effectively I can use my paints.

Cadmium red is an opaque, powerfully tinting, chromatically intense pigment. I used it to build up the rich, warm color behind the rabbit in English Rabbit and Keats (egg tempera with oil glazes, 10⅛x8½). Along the edges of the red, I applied dozens of very thin layers of alternating burnt umber, quinacridone scarlet and viridian. These transparent colors added depth and created the shadow effect. For the gold-toned lettering, I used a metallic, powdered pigment. Dozens of these pigments exist, imitating the look of copper, gold, brass, silver, various patinas, opalescence and more. They’re colorfast and nontarnishing and can be used for making paint from scratch or added in small amounts to tube paints.

Over time, if you’re attentive to your colors’ behavior and do a bit of research, you’ll become familiar with the distinctive natures, strengths and weaknesses of your pigments and learn to use them to their best technical and aesthetic advantage. I’ve discovered that creating tables with the characteristics of my palette’s pigments helps me keep everything straight and allows me to record new discoveries easily. Below is a list of 16 characteristics that give each pigment its unique nature. You can see how those characteristics can be applied to a specific pigment by referring to the sample table for titanium white.

Pigment characteristics

Common name: This is the name (or names) by which a pigment is traditionally and commonly known.

Colour Index International name and number: The Colour Index, an internationally recognized system for identifying pigments, assigns consistent Colour Index names (CI names) and numbers (CI numbers) to all artists’ pigments. The CI name—derived from the part of the spectrum to which a color belongs, followed by a number—is more commonly used. For example, cadmium red has the CI name pigment red 108, abbreviated to PR108. The CI number for cadmium red is 77202.

Manufacturers sometimes give descriptive names to paints, such as forest green or fire engine red, in the hope of seducing you into buying those colors. Such names may tell you nothing about the actual pigment inside. A reputable company always provides the CI name (and sometimes the CI number) to help you identify exactly what pigments were used in the manufacture of that paint. Knowing your pigments’ names lets you assess their quality and working properties (such as permanency, opacity or transparency).

Inorganic or organic: A pigment is either mineral based (inorganic) or carbon based (organic). Inorganic pigments are derived from native earths (natural deposits mined from all over the globe), minerals or metallic compounds. Organic pigments are derived from living or once-living materials: plants, animals or petrochemicals (coal-tar-based chemicals). Knowing whether a pigment is organic or inorganic gives you many hints about its characteristics.

Natural or synthetic: A pigment is either found in nature (natural) or is manufactured in a laboratory (synthetic).

Composition: This is the chemical make-up of a pigment.

Origin: This can refer to the geographical source for the raw material or the pigment’s manufacturing process. Some pigments are calcined (heated), which can occur naturally (by volcano) or through manufacturing (in a furnace). Calcined pigments have less water content and are warmer and more transparent relative to their uncooked state. For example, burnt umber is a warmer and more transparent version of raw umber.

Historic or modern: Prussian blue, first manufactured in 1704, is considered the beginning of the modern era of pigments. Historic pigments are those that have been in use at least since the Renaissance and maybe as far back as prehistoric times. A brief history of the pigment may be included in your chart.

Opacity or transparency: Opacity provides hiding or covering power. Transparency allows for glazing. A pigment’s particle size and structure contribute to its degree of opacity or transparency. Manufacturers are not consistent in how they describe these qualities—one company may label a hue semi-opaque while another company labels the same hue semitransparent. With practice, you’ll learn the degree to which light passes through your palette colors.

The tapestry in Vincent Mikel (egg tempera with oil glazes, 10⅝x7½) is several shades of yellow ochre with a bit of cadmium yellow. Yellow ochre is a delicate color—I needed about half a teaspoon of powdered pigment to do the job. Cadmium yellow, on the other hand, is a powerhouse. A pinprick amount affected the yellow ochre. If I’d switched the proportions, the cadmium would have swallowed up any trace of the ochre.

Tinting strength: How powerful is the color? Pigments with high tinting strength retain their influence when mixed with other colors.

Shade: What is the color’s inclination? Is it warm or cool? Does it tend toward blue or green or another color?

Particle size: Individual pigment particles are measured in microns. The larger the particle size, the more likely the pigment is to sink and separate when mixed with water. The weight of the material from which the pigment is made is also a factor; mineral pigments are heavier and more likely to sink. The smaller the particle size, the more likely the pigment will float and possibly need a wetting agent in water-based media.

Smaller-sized pigment particles may need to be more thoroughly ground to fully disperse and release their color in paint made from scratch. Smaller particle size also generally indicates greater tinting strength, not to mention a greater tendency to stain hands and clothes (Prussian blue is notorious for this).

The uniformity of modern, mechanically ground pigments is a great convenience; however, modern colors may lack some of the unique qualities of their hand-ground historic counterparts. Certain pigments look best when ground into large, irregularly shaped particles; they refract light differently than a layer of same-sized particles would. Medieval colorists knew how long to grind a pigment in order to bring out its most beautiful hue. For this reason, some artists prefer to make or buy paint that includes hand-ground, historically accurate pigments.

ASTM rating: The American Society for Testing and Materials International (ASTM) rates pigments on their performance—most importantly, a color’s permanence or its ability to withstand exposure to light without fading. A rating of I is excellent; II is very good; III is not satisfactory. Impermanence used to be a problem with some organic colors, but most high-quality artists’ colors are rated I or II these days.

Toxicity: Paint may enter the body by ingestion, breathing and absorption through the skin. The effects of toxic pigments on an artist’s health may be acute or chronic, so knowing which colors are potentially harmful is important. The Art and Creative Materials Institute (ACMI) works with independent toxicologists to evaluate materials for their toxicity. Not all pigments have been tested, but those that have should be labeled as either AP (approved product—certified to contain no materials in sufficient quantities to be toxic or injurious to humans) or CL (cautionary label, toxic).

Note that regardless of their inherent toxicity, all dry, powdered pigments are irritants to the lungs and, therefore, hazardous. Always use a respirator and gloves when handling pigments in powdered form. Once suspended in a liquid (such as in water and egg for tempera or in oil for oil paint), a pigment can no longer travel into your lungs, and a respirator is not necessary.

Comments: Include additional notes under this heading, such as whether a pigment is slow- or fast-drying, brittle or flexible, or in need of a wetting agent.

Expense/availability: Note whether the general cost is high or low. Be aware that some of the more heavily mined earth colors are getting harder to come by; very toxic pigments also may have limited availability.

Supplier/order number/price: List the supplier from whom you bought the color, as well as the order number and price. Different art stores may sell pigments by the same name, but the pigment’s color may vary slightly from one source to the next. Note that some companies sell their powdered pigments by volume; others, by weight (100 grams of pigment, regardless of volume).

A board member of the Society of Tempera Painters, Koo Schadler conducts workshops on egg tempera and old master painting. Author of the book Egg Tempera Painting, she’s a master painter of the Copley Society of Art in Boston. For more information about her book and her work, visit www.kooschadler.com.

This article appeared in the May 2009 issue of The Artist’s Magazine, which is available for order as a digital download. Click here to learn more.

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