Thanks for all the input. We discovered one additive that might be even
more effective than cayanne pepper. It's called Omadine, produced by
Arch Chemicals. There are some test results available on the web, and
they look pretty good. However, in the end we didn't follow any of the
great advice we got here, because we found a tin-based self-polishing
paing here in Turkey. And we bet tin is best.