Colour in Art: Pigments

Dyes and paint pigments are the two main colorant materials.
A dye is absorbed by the material to be colored, whereas a pigment is applied to the surface. Pigment are usually highly insoluble substances. The natural pigments are nearly all minerals found in the earth. The earliest natural pigments, found in prehistoric cave paintings, were the yellow, brown, and red earth colors. These materials are found on the modern artist’s palette as yellow and red ochre, raw and burnt sienna, umber, Venetian red, and Indian red, which are all forms of clay containing compounds of iron.

In sites of the Upper Paleolithic period in France, dating from about 40,000 B.C., caches of iron oxide powder were found that had been heat-treated to modify its color. This marks the earliest known example of pyrotechnology from which have emerged techniques for producing a rich variety of pigments and glazes for pottery.

As in prehistory, some pigments are simply rubbed onto a surface to color it. A pencil consists of a core of compressed graphite that breaks up into fine particles when rubbed on a rough surface. Graphite, being pure carbon, the major constituent of coal, provides an effective black because the small particles reflect light between each other many times before it can reflect back to the viewer. Some pigments are applied to a surface as suspension of fine particles in a liquid carrier, and the particles remain weakly attached when the liquid evaporates. Watercolors are examples, but the water carrier also contains a glue to help attach the pigment.

Source: Samuel J. Williamson, Herman Z. Cummins. (1983) Light and Color: In Nature and Art p. 343- 350

Pigmentation and Painting

Pigments as the basis of paints have been used for thousand years. Early pigments were ground earth or clay made into paint with spit or fat. Until now pigments are created by chemical engineering.

In most paintings, the pigments are suspended in the paint media. Common media include oil and egg yolk. Both substances undergo chemical change in the air, and convert into a plastic-like film. Although called “dying,” what is really happening is a chemical change (so called “polymerization”), which makes the media hard.

Until paint was produced commercially during the Industrial Revolution (circa 1800), painters had to make their own paints by grinding pigment into oil. The paint would harden and would have to be made fresh each day. Paint consists of small grains of pigment suspended in oil. Although it appears smooth to the naked eye, on a microscopic level, particles of pigment are suspended in oil, as fruit in a Jello mold.

Oil paints do not “dry” by evaporation (as do watercolor paints); rather they harden through chemical reaction, as a Jello sets. Contact with the air causes oils to oxidize and to crosslink. The paint sets and hardens over time. Paints of different pigments dry at different rates. Charcoal black retards the drying (creating a slow-drying paint); ochre accelerates the drying (producing a quick-drying paint).

This link shows the history, manufacture, and technical details of example of use of specific pigment colors:

 http://www.webexhibits.org/pigments/intro/pigments.html

This link records the overall developments of pigmentation from prehistoric to present with a timeline:

 http://www.webexhibits.org/pigments/intro/history.html

Source from: http://www.webexhibits.org/pigments/intro/index.html