Silverpoint is done with a very thin silver wire inside a holder, so it works pretty much like a pencil. You scratch away at a specially prepared surface, and with each stroke you deposit a little more silver. Over time, it tarnishes and becomes richer and deeper in color. Right now I'm working on a companion piece to another one with the same subject matter; two doves out in the back yard.
I think I should send a thank-you to Jos. A. Smith, my drawing teacher back in my undergrad days, for introducing the class to silverpoint. It really is a great medium to work in. Here's what the tool looks like: