Cabbing is the active verb form of the word cab. A stone cab, also known as a cabochon, is a stone that has been tooled or cut into a smooth dome without facets. Both precious and semiprecious gems may be cabbed. Cabbed stones also feature a 45-degree shoulder around their edge that aids in setting it into jewelry pieces.
Cabbed stones may be any shape or size, as long as they are domed on one side and flat or convex on the other. The shoulder on cabbed stones allows for easy setting into a bezel. The bezel is the metal band that holds the stone to the piece of jewelry. Large stones are ideal for pendants, while smaller ones may be set into earrings or bracelet charms.
The first step to a beautiful cabochon is to choose the stone slab. The stonecutter uses a marker to mark a template on the stone, choosing the most attractive arrangement of pattern for the finished piece. The marked shape is then cut out using a trim saw and cooling lubricant to keep the saw blade from becoming too hot. More exact cuts can be made using a small band saw.
Next, the stonecutter uses a grinder to achieve the basic cabochon outline. This removes any excess stone missed by the trim saw, and rounds the edges of the stone. The stone is moved back and forth against the grinding head on the machine until the desired shape is attained. During this step, the stone shape is finalized.
The dop stick is a stick that is dipped into hot wax and attached to the back of the cabochon. This allows the stonecutter to keep control of the stone without losing skin or nails to the polishing wheel. Once fixed to the stone, the stone and stick are heated to bond the wax to the stone surface. When it is time to remove the stick after shaping and polishing, the whole thing is put into a freezer for a short time to make the wax brittle and break the bond.
The finished shape of the cab is produced using a diamond lap of varying grits, like sandpaper, attached to a lapidary machine. The number of the grit depends on the stage of the cab as well as the hardness of the rock. The lap spins, and the rock is swept over it in a back and forth “J” motion, turning about a quarter turn with each pass. The stonecutter repeats this, changing the lap grit as necessary, until the smooth dome is formed.
The stone is washed free of all grit and dust and a felt polishing pad is placed on the master lap. The stone is polished either with dabs of diamond compound or lines of a cerium oxide slurry placed on the felt pad. As the pad spins on the lap, the polish is incorporated onto the surface of the cab until the stonecutter is satisfied with its shine.