Let me stand next to your fire: how to evaluate the unique colors of opal.

How do you determine the color of a gemstone that is known precisely for its multi-colored qualities? Opal is such a stone, and, consequently, several factors have been developed for that purpose. The important color signifiers for opal are:

1. Type and body color. (Black is the most valuable type and body color.)
2. Play-of-color. (Red play-of-color against a black background is most prized.)
3. Brilliance. (Play-of-color which keeps its brilliance even away from direct light.)
4. Color pattern. (Large flashes of brilliant color are most desired.)
5. Transparency. (Opaque is favored for black opal, while transparency is preferred in the lighter stones.)

Black opal can have a black, gray or blue body color, and to determine the actual body color, you must examine the stone from its face-up (looking down over the top) view. The most valuable of the black variety will be opaque with large flashes of brilliant red play-of-color visible within the stone even away from direct light. The top quality specimens in this category can sell for well over $10,000 per carat.

To put cost in perspective, though, some of the lighter opals will only cost between $5 and $300 dollars per carat. But the highly transparent light opals with brilliant play-of-color are called crystal opal, and can cost over $2,000 per carat.

There are also boulder opals (shaped and sold still attached to the stone on which it grew) matrix opals (traces of opal make lovely streaks within the host stone) and fire opal (not to be confused with black opal where brilliant red play-of-color is present. Rather, fire opal has a red, orange or yellow body color.)

When examining opal's color, it is best to hold the stone over a black background so any light shining through will be absorbed. Any light reflected back into the stone will give you a false impression of the actual colors present in the particular specimen.