Sometimes when cutting a cabochon from softer gemstone materials it may be a good idea to cement a back to it.
This is often done to stabilize or strength a stone. Various backings may also be used to enhance a gemstone, add color to clear stones, utilize a piece of gemstone that is not stable enough or pretty enough on its own, reduce the price of an expensive gemstone material, create a unique new gemstone, or generate an unusual color combination.
When a stone is backed, it is sometimes referred to as a doublet. Opal doublets are very common. Sometimes opal only comes in very thin veins, so a back is added to stabilize it and occasionally a clear top of quartz is added to protect it or finish off the cabochon. When a top is added it is called a triplet.
A stone cabochon backed for stability is not considered a fake gemstone. Many attractive gemstones would never be suitable for jewelry if not for this process.
Stones may be backed with any hard stone. Black chalcedony or basanite work well. Plastic or old records work will too. A 2-part 5-minute epoxy cement is the most common sealant.
You should go ahead and cut and finish your cabochon first. Cabochons that are going to be backed should be not be polished on the bottom and only finished to 400 grit. If using natural stone to back, you should also preform it out to the same shape as your cabochon. Plastic does not need to be preformed. Then glue the cabochon to the backing. It is best to coat both the backing and the cabochon with the epoxy. Then firmly press them together. It may be necessary to clamp the stone while drying, but be careful not to tighten too tight. Make sure you give it plenty of time to dry thoroughly. When dry, if applied neatly you should be able to go straight to a grinder, if there is lots of excess use a lapidary saw to trim the edge before moving to the grinder, then finish out the entire stone.
Some jewelers will use plastic or other substances such as jb weld, devcon “plastic steel”, devcon “liquid bronze”, or even their own secret recipe.
The backed stone can be set into any type of setting, including prongs. Setting these cabochon stones in a bezel can hide the backing if it bothers you. A bezel protects fragile stones better anyway.
Thanks for reading!