Iridescent Colors Williamsburg makes a line of iridescent colors that are both colorfast and permanent. They are made with ground mica so that even the "metallic" colors will not tarnish. There are some limitations inherent in the composition of these colors: in order to refract light and appear metallic or nacreous the mica particles must not be ground too small. They should be almost like tiny crystalline prisms sparkling with glints of light. Because of this the paint has a semi-translucent quality - not the heavy covering power of aluminum radiator paint. Interference Colors Imagine the colors that shoot out of a fire opal except each color isolated. For example interference violet goes on like an almost colorless glaze but violet picks up and reflects the light. These interference colors work best in glazes - they lose their opalescent sheen when mixed too much with other colors.