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 more colors, the better. In black opal and white opal, the color people usually like the most is red, the next is purple, orange, yellow, green and blue. In the flame opal, purple, green and blue are the best. Because the contrast between these colors and their background colors are very strong, making the colors more brilliant. When the special high quality opal is twisting, the color can also be changing and moving continually, making you feel like in the dream of colors.
(3)    The Size of Color Spot and Shape: In the opal, according to the color of chatoyance color spot, we can divide opal into single color (basically composed of one color), three colors (composed of two or three colors), five colors (basically composed of the colors from red to purple, just like the rainbow). It is usually considered that the one with big spot and many colors is high quality. Besides that, the shape of the color spot is also very important, like some color texture takes on flowery; some takes on flamboyancy etc. The value of the opal with this kind of color spot is much higher than that without the color spot.
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