Evaluating the quality of opal mainly depends on the following three factors:
(1) The color of Background: As for evaluating the quality of quality, it is generally considered that the background with deep color (smoky gray, brown, blue, black etc.) is better than that with light color (light white and bright grey), it can better show the chatoyance of opal. The value of high quality black opal can be higher than that of sapphire.
(2) Type of Color: In an opal, the 더 많이 colors, the better. In black opal and white opal, the color people usually like...
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