As a rider to the reed voicing thread:  if while experimenting with
the curvature of a tongue the brass is curved and straightened several
times, a mild hardening occurs preventing the tongue from ever attaining
the correct curve.  The only solution is to scrap the tongue and start
again with a fresh -- very flat -- piece of brass.

Normally "half-hard" brass is used, and the curvature is achieved by
clamping the tongue onto the burnisher (a flat piece of hardwood) at
its root end, and is curved with a single stroke from the clamped end,
to the tip.  The ideal burnisher is a cigar-shaped round tool with
handle.  Its slightly convex surface helps to keep the burnishing
pressure central on the tongue, preventing a twist of the curve.

Successful reed voicing is a skill achieved after much practice, and
after a lot of tongues have been thrown away!

John Page, U.K.