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Silver, being whiter than platinum or palladium, is quite suitable for color as a metal in mounting diamonds, but it is seldom used now on account of its ready oxidation. Despite its easy tarnish, it was used in much Victorian jewelry, such as spray brooches and pieces which contained a large number of small stones. A light yellow tint in a stone would be neutralised by platinum mounting, but lumpy stones look leaden and heavy in this metal. The high cost of platinum in recent years has led to the increased use of palladium in jewelry, and this lower priced metal gives excellent results.

Mounted stones lose much of their brightness and luster if grease or dirt is allowed to accumulate behind the settings. A stone must be surface clean to show its full brilliancy. There are various obvious methods of washing away dirt from behind a stone. The use of an old, soft toothbrush, soap (preferably vegetable soap), and warm water will not injure diamonds, but careful washing in dilute sulphuric acid will clean a stone of most of the attached foreign matter. Better still, it may be boiled in an aqueous solution of sodium hydroxide, dried, and then rinsed in pure commercial alcohol. Or it may be boiled either in a strong solution of potassium hydroxide or in a mixture of two-thirds sulphuric acid and one-third nitric acid (aqua fortis). Washing in benzine or gasoline, followed by rinsing in alchol, is satisfactory, but dust and dirt are not entirely eliminated by merely dipping in alcohol.

Black opals should possess an abundance of red flashes, or pin point flashes, to be of first quality. If the reds are mixed with greens, they are also good, but broad, even colors are not so valuable. If the brown matrix is showing, the value of the stone is still lessened. Even smaller pieces of fine black opal are comparatively rare, that is, stones weighing three or four carats, and $140 (£50) a carat is not a high price for fine qualities. One should beware of black opal doublets, which are frequently seen in good class jewelry. They may be just as attractive as the natural stone, but their commercial value is far less.

In white opals, the most usual variety in use, the background is a milky tinge, whitish, bluish, or greenish, but the best specimens show such a wealth of red flashes that this bodyground is hardly seen. Stones which show red and green, and also only green, are considered good in quality, but the play of color must be strong and not reserved to parts of the stone only. Bluish stones are of not much value, and thdse which are almost all milky white without any color relief are unsaleable.