Turquoise is also deepened in color by artificial means, aniline dyes being sometimes used. But the coloring matter soon fades, this type of dye being most unstable. Quartz cat’s-eye is also stained a dark blue and also pink, both unnatural colors to this stone. We have already noted that heat applied to smoky quartz, amethyst, zircon, topaz, and other stones affect their color, and that iris quartz is obtained by a dye being introduced into artificially created cracks within the material. Coral and mother-of-pearl are both stained to improve their color, aniline dyes being used. Some new coral is covered with a varnish after being colored, but this wears off in course of time.
Much of the so-called “antique” amber, and “Chinese” amber is the result of staining new material to simulate the dark brown and clear red varieties, which are much liked. The rough is immersed in oil to which coloring matter has been added, and then gently heated for some days. After being dried, cleaned, and polished, the amber will be found to have absorbed the coloring matter, although often only superficially. Amber is very brittle, so unless the heating is carried out very gradually, the material will split or crack. The colors obtained are often very similar to the natural shades, but they are seldom permanent. Such amber is sold at an enhanced price.
A green color is sometimes seen in the clear or semiclear amber, while compressed amber, which approximates to a reconstructed amber, may be stained to any color. A green very much like that of Chinese jade is sometimes seen, but as amber is softer and lighter than any stone, there is no difficulty in distinguishing it.