PRECIOUS OPAL 377 



play of colours over the whole surface of the cut stone, often presents a problem of 

 considerable intricacy. 



By the employment of various devices the play of colours of precious opal can be 

 increased to a certain extent ; thus, for example, a cut stone, which is not too thick and 

 opaque, may be placed upon a variegated foil, a piece of a peacock's feather, or a bright, 

 polished plate of mother-of-pearl. The stone is rarely mounted a jour, but is best set in 

 a black case and surrounded by a border of small diamonds or of coloured transparent 

 stones of some sort. In the same way, the effect of a large diamond, ruby, or sapphire is 

 greatly increased when set with a border of small opals. 



Opal is a precious stone for which there is a considerable demand, and it consequently 

 commands high prices. The value, as we have seen, depends in part upon the character of 

 the play of colours, those in which red and green are predominating colours having been 

 specially favoured, though this may be but a fleeting preference. A perfect stone should 

 be neither too transparent nor too opaque, since in both cases the play of colours will be 

 less brilliant ; neither should it be cut too thick or too thin. Until recently the price of 

 the larger and better specimens of opal was governed in the trade by their special qualities 

 and size, and not according to their weight. Now, however, the weight of a stone expressed 

 in carats is one of the factors which determines its price. Fine Hungarian stones are 

 almost equal in value to brilliants of the same weight Large opals, especially those with 

 a considerable thickness, on account of the relative rarity of their occurrence, are dear, and 

 the price of still larger stones is more than proportionate to the increase in size. A carat 

 stone showing a brilliant play of colours is worth at least 50s. ; stones which are inferior in 

 this respect, as is the case with many of the so-called "Mexican" opals from Central 

 America, are worth very nmch less. In the middle ages precious opal of fine quality was 

 probably valued still more highly than it is now, and the stone was held in high esteem by 

 the Romans. 



No successful imitation of precious opal in glass has hitherto been achieved ; any 

 imitation can be instantly distinguished from the genuine stone by the appearance of the 

 counterfeit play of colours. More successful attempts are sometimes made by mounting 

 common opal upon a variegated foil in a blackened case, a fairly good imitation of the play 

 of colours of precious opal being thereby produced. Black opals with a brilliant play of 

 colours sometimes appear on the market ; it is probable, however, that such stones have 

 been treated in some way unknown. 



The occurrence and mode of origin of precious opal differ in no wise from those of 

 common opal. Everywhere the various kinds of common and precious opal occur in 

 association with each other and with other minerals consisting of silica, such as quartz and 

 chalcedony. It occurs as small patches in larger masses of common opal, and there is a 

 gi'adual passage from one variety to the other ; in the winning of opal those portions 

 showing a play of colours are sought for and extracted from the main mass of valueless 

 material. 



By far the most important opal locality, and the one which yields the most valuable 

 material, is the neighbourhood of the village of Czerwenitza (Hungarian Vorosvdgas) in the 

 Tokaj-Eperies Mountains, near Kaschan and Eperies, and in the Saros Comitat in northern 

 Hungary. The mines are located on the Simonka mountain (Dubnik Hill), and especially 

 on the Libanka mountain. The opals found here in former times were sent to Constanti- 

 nople, and from thence found their way to the cities of the west, especially Amsterdam. 

 This circumstance gave rise to the belief current till the end of the eighteenth century that 

 the opal was found in the East, and accounted for the stone being known as " oriental opal." 



