Page:A treatise on diamonds and precious stones including their history Natural and commercial.djvu/180

144 impositions are practised with regard to the emerald, by covering green glass with a plate of white topaz. This, as well as all other imitations of colored stones set in jewellery, formed by means of the white topaz, may be discovered by the methods above described.

, in which the color is uniform, made to imitate precious stones, may be detected by its being easily abraded by the file, which has no effect upon the real gem.