Consistency and Directionality
Consistency
Consistency refers to the uniformity of brightness, color and pattern. This can also refer to the density of the fire and the color of the background. Brightness is judged by the overall impression the gemstone gives, but the one bright spot in a corner is ignored. Now look at each of these characteristics and note if it is consistent across the gemstone. If it is inconsistent, judgment is called for. Does the inconsistency add to or take away from the beauty of the opal? In most cases, a little inconsistency adds to the character of the gemstone and makes it more attractive. Such inconsistencies should only be faulted when inconsistency causes an opal to be less attractive.
Directionality
Directionality of fire refers to whether the fire shows as brightly from one direction as it does from another. Almost all opals will have some directionality in the brightness of fire. Some opals want to be rings (those that look brightest when looking straight down on them), and others want to be pendants (those that look brightest when held vertically and slightly behind the light). Most gemstones look best from one particular orientation. A truly non-directional opal will appear equally bright no matter what direction you tilt it. Many gemstones will appear somewhat brighter in certain directions than in others. An opal that looks bright from a direction which is not seen when it is worn is a less valuable gemstone. If the change is small, the gemstone would be graded slightly directional. If the change in brightness is at least one brightness level, the fire would be graded somewhat directional. If the gemstone loses most of its color from some directions, then it would be graded very directional. If it loses all of its fire in some directions, especially if it only shows good color from one direction, it will be graded highly directional. The more directional the gemstone, the less valuable it is.
