Will, the only way I can think of to do what you want would be by
chemical milling, which amounts to etching or electrostripping.
In principal what you'd do would be to bend your material into a U
shape, and gradually lower it into the etch bath, a little bit at a
time. So, the part that enters first gets etched for the whole
time, and the part that is submerged last gets only a short etch.
When it's done you'd straighten the wire.
In practice there are all the usual "ifs and buts and maybes"
associated with etching. The wire would have to be uniform throughout
its length, not just in composition but also in terms of hardness.
You'd need to stir or agitate the liquid, probably. You'd need to
experiment with different rates of lowering and various total etching
times. It's possible to envision variations that would keep the wire
straight throughout the process, but they would be more applicable to
For silver you could use dilute nitric acid or ferric nitrate
solution. For other metals you'd need an appropriate etchant.
Electrostripping is like electroplating in reverse, in fact that's
just what it is. All chemicals have safety issues associated with
them, which I'm not going into here, just pointing out that there's
more that you need to be aware of besides the basics of the method.
Incidentally, this technique is used to make extremely fine points
on various wires for scientific purposes.
Kevin (NW England, UK)