What are opal triplets?
 

One of the most inexpensive ways to enjoy the beauty of the opal is to buy what are known as triplets. A triplet is simply a very thin slice of natural opal, sandwiched between a clear glass or quartz cap, and a plastic or stone backing. The clear cap magnifies and protects the opal slice, and the backing enhances the color of the opal. The whole idea is that even low quality opal can be made to look like high quality 'black opal', and can produce many inexpensive, but very marketable stones.
   
 

Although you could make triplets out of low-grade opal, all you would get is low-grade triplets. Better grade and 'gem' grade triplets are made by starting with very fine or gem grade rough opal stone.

The rough stone is held against a field of parallel diamond grit saw blades and pushed into the blades by the "hold down arm", a machine that produces the intricately thin slices. The blades are carried in a changeable block that allows one to choose the spacing between the blades, varying the thickness between 70 and 120 slices per inch. It takes between 3 and 15 hours for the saws to cut through the rough stone, and during this time the machine must be monitored to make sure that it has not gotten clogged. Not only can you lose the opal stone, but you can destroy the very expensive saw blades.
 

Because they are going to be sliced, the rough stones must be fairly large. Smaller stones cannot be held easily against the blades. White-based opal occurs commonly in larger stones, but remember that this process doesn't produce the fire. The color, pattern, and fire must already be inherent in the stone itself..

After cutting, the slices are sorted and graded, and either broken or sawed into sizes and shapes appropriate to their pattern. Then, the three pieces of the triplet will be glued together with a very fine jewelers cement, and left to cure. It is not necessary to polish the opal slices because the glue will fill the slight imperfections and provide the perfect refraction index. Next, each of the rough triplets are ground and polished. Some will become 'freeform' shapes, and others will be ground to calibrated shapes and sizes.

Properly done, the quantity and the effort will more than make up for the differential in cost. The result produces a large number of triplets which can be sold at a very reasonable price.