The CIE L∗a∗b∗ coordinates calculated using<br>GRAMS and Adobe Photoshop software yielded a<br>purple color (figure 6, center), consistent with the<br>bodycolor of the opal. This proved that the coloring<br>agent of the purple opal can be partially removed<br>with acetone, and since we know of no naturally<br>occurring coloring agent showing this behavior, we<br>concluded that the opals are colored by an artificially<br>introduced dye
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