Any Opal will lose its play of colors on being heated too highly, hence possessors should avoid subjecting them to more than ordinary heat. It is the variety and brilliancy of their changing colors which give to Opal nearly all its desirability as a precious stone, for, as has often been remarked, the qualities of hardness, transparency and rich body color which give to most other gems their value are lacking in the Opal. But together with the beauty of its changing colors Opal possesses an advantage over all other gems in that it cannot be successfully imitated. It is said that the Romans were able to make artificial Opals closely resembling the real, but, if so, the art has been lost never to be recovered, and we may hope it never will be. Hence, however much danger there may be in buying an Opal that it has not been properly “seasoned,” or may not retain its color, the purchaser may at least be sure he has an Opal and not an imitation. The stones are usually cut in the oval form known as en cabouchon, this cutting being found to bring out their brilliancy better than any facetted form. The brilliancy of the stone may be increased in setting by giving it a backing of mother of pearl or black silk. When a number of Opals are placed together they seem to borrow brilliancy from one another, a fact which is taken advantage of in settings by placing a number together and also by Opal dealers to dispose of inferior stones by grouping them with good ones. For this reason when Opals are purchased they should be examined separately. The value of Opals depends almost wholly on the brilliancy of their coloring and their size. Stones without the play of colors are practically worthless, while stones of ten to twenty carats’ weight, with brilliant coloring, may bring several hundred dollars. The most highly valued Opals have long come from the mines of Czernowitza in northern Hungary. These Opals are often known as Oriental Opals from the fact that in early days they were first purchased by Greek and Turkish merchants, and by them sent to Holland. There are, however, no localities in the Orient where precious Opals are found. The rock in which the Hungarian Opals occur is eruptive, and of the kind known as andesite. It is considerably decomposed, and the Opal occurs in clefts and veins. There is little doubt that it was from these mines that the Romans obtained the Opals known to them, and the output has been quite constant since.