black opals command the highest prices and should have as dark a background as possible with maximum variety and intensity of colours.
The matrix should be translucent. Red is always a desirable colour. If possible the patches of colour should be evenly distributed over the stone and be even in size. Traces of milkiness detract from value. Some of the finest Mexican opal, resembling water opal, is faceted and shows a play of colour by both reflected and transmitted light. This variety has been called contra luz opal. Watch beautiful opal specimen