Copper has traditionally been used for very small carving points. Diamond and copper have a natural affinity for each other that makes charging these tools easy. Brass makes wonderful tools, but it should only be used with fine abrasives. Its softness makes it hold the abrasive but also limits this metal's durability. It is readily available in appropriate sizes.
Sintered steel offers the best of two worlds.
It's durable and also holds the abrasive well because of pore spacing, which tends to lock the abrasive to the metal's surface. It can also be easily fashioned into tools. Powdered bronze mixed with diamond abrasive is a material used as the bonding agent of sintered diamond tools, although it is not used as a tool material directly. The diamond and the powdered metal are combined, pressed into a mold of the desired shape, and then fused together in a furnace in a reducing atmosphere. These tools are the most effective for gem carving.