Q: I would like to enlarge the holes in some freshwater pearls. Any suggestions about how to do this?
A: An ordinary high-speed drill bit, such as you’d use with metal, will work with pearls as well. Use it at reasonably high speed with only a little pressure. Using really slow speeds will tend to jam, or can chip the pearl. If you’re going all the way through, go halfway through from each side, so it doesn’t chip out the back end of the hole on exiting. A little lubricant of your choice will help. (I just use saliva).
The drill must be sharp. Dull ones just heat up. And it won’t last very long before it gets dull, drilling pearls. But for only a few, this works just fine. For larger quantities, a carbide drill bit will work very well. These require high speeds, though, and you must use them with care, as they are brittle and easily broken. But they are generally what the “pros” use in the pearl industry.
You can also use diamond bits. These are either the lapidary type wire drills, with a little diamond grit plated on the end of a piece of music wire, or a more precisely made bur type diamond point. Be sure to use with water, both to keep the pearl cool, and the bit as well. While diamond points work well enough, they seem like “overkill” for this relatively soft material.