Bismuth oxychloride. The same bismuth used by the ancient Egyptians to make Nefertiti's cosmetics found broad applications in the modern cosmetics industry. Used since the beginning of the century as a polishing powder in the manufacture of artificial pearls, bismuth oxychloride was more recently manufactured in crystalline form to produce the basis for pearl luster cosmetics. Unfortunately, bismuth is somewhat light-sensitive and darkens with time, which prevented it from meeting some of the growing demands of the plastics and coatings industries. Although bismuth is still used for some industrial applications, attempts to improve its lightfastness are ongoing.
Metal-oxide mica pigments. The break- through for creating synthetic pearlescence came in the 1960s with the invention of the metal-oxide mica pigment. In this process, titanium dioxide was deposited on thin layers of fine particles of mica-a natural mineral. Color changes were achieved by increasing the thickness of the titanium dioxide layer. This process was able to yield uniformity, even in large scale industrial production, and the manufacture of these synthetic pearl pigments revolutionized the plastic and coatings industries. In addition to introducing a remarkable new palette of colors, the synthetic pearlescent pigments possess many characteristics appreciated by artists. They are heat and acid resistant, display outstanding lightfastness, are non-toxic and non-polluting.
In order to benefit most from this section, I suggest you have a few interference colors on hand (D.S. Interference Oils or Golden Interference Acrylics), some conventional colors of the same medium, a palette, mixing knife, brushes and some heavy paper or gessoed canvas, black and white. An old painted canvas, which you would otherwise paint over or throw out, makes an excellent testing surface for further experiments with interference colors.
Test 1: Paint out two strips of interference blue (for example), one on a black surface and the other on white. Note the results. The color becomes bluish on the black surface because black absorbs all incident (striking) light and reflects none; on the white surface, it appears as a silvery white, devoid of blue, because the white surface absorbs none of the light and reflects all. Now take the painted white surface and tilt it to the light until the strips appear yellow-the complement of blue. If you used interference green, instead of blue, your strip should read red as you tilt it into the light.
Test 2: On your palette, mix the same interference blue with a touch of black. Paint a strip on each of the two surfaces, black and white. Note the results. The blue is deep and apparent on the black surface. With the addition of the black, the blue color emerges on both surfaces, because more light is absorbed.
Test 3: On your palette, mix the same interference blue with a touch of a conventional blue, such as phthalo. Paint a strip on each of the two surfaces, black and white. Note the results. The blue comes to life with a remarkable brilliance on both surfaces, although it is again more apparent on the black. While the intensity of the blue is increased by the addition of an absorption pigment phthalo blue), the pearly luster is decreased. Still, the mixture maintains the dimensional effects of an interference pigment. Tilt the paper to pick up various angles of light and you will see a different blue with each turn. Now try this same test mixing interference blue with other conventional blue pigments, such as indanthrone, Prussian, cobalt, ultramarine and anthraquinone. Note the results. Try adding reds, yellows and greens.
Test 4: On your palette, mix the same interference blue with a touch of a yellow- its complement. Paint a strip on each of the two surfaces, black and white. Note the results. On black, you can see how you get a play of blue and yellow; on white, you get a silvery yellow. Both surfaces reveal the dimension typical of interference colors.
A Note on Surface Color: These tests show that by combining interference colors with conventional absorption colors, you can use them successfully on both light and dark surfaces. While the effects will be strongest against black, all dark surfaces provide a background for setting interference colors ablaze. Whether you paint by scumbling layers of color or by applying delicate veils of glazes, you can have the three-dimensional quality of interference color without metallic or pearlescent effects. By overpainting an old canvas with combinations of interference, absorption and even metallic colors, you can observe the numerous options possible for bringing the glow of full-bodied color to your work.