bobr@zeus.UUCP (03/29/87)
Gold, silver, copper, obsidian, etc., are not color per se, but gradients of colors which reflect the nonuniform reflectance properties of those materials. The colors and intensities actually vary with respect to the angles of incidence and reflection from the light source. Rob Cook wrote an informative paper on this subject for a SIGGRAPH conference a number of years ago. I can't cite the exact reference but it was before 1982. -- Robert Reed, Tektronix CAE Systems Division, bobr@zeus.TEK