White opals
All opals, and particularly white opals, should be judged in a good light. They will appear better under artificial light and to a disadvantage in a dull light. Stones may be cut in any form, and they are often thin. If too thin, they may be difficult to use. Odd shapes will also have some bearing on value; they may need to be re-cut, which involves extra cost, besides loss in weight. Opal, however, has a comparatively low specific gravity, so one should be careful of overestimating weights. Doublets of white opal are not so common as those of the black variety.
Fire opals are not in great demand at present. The best qualities are those having a uniform deep orange red color. Orange yellows and paler stones are of little value. Milky tinges or clouds within the stone are further detractions. The name of this stone is misleading since many think that it refers to an opal showing much “fire.” But it is properly used only in connection with those opals which possess the one color—orange red, or a slight variation of this color, throughout the material.
Water opals are most attractive if fine. But if they are almost transparent and without any play of color, they are valueless. Large, fine stones are rare. Their body is almost transparent, perhaps slightly milky, but the essential is the play of color which seems to come from within the stone, and not from the surface.