gillymore wrote: I took a classical guitar course and the instructor swore by small a amount of talcum powder worked well into both hands....

Talc is very good at absorbing moisture. If one's problem is simply sweaty fingers, it should work well. But it does not prevent sweat, it merely soaks up the water. So if one's sweat contains a chemical that damages the strings, it will have only partial effect. Not no effect, because the acidic chemical won't spread as quickly without water. But ideally one wishes to either suppress the string-damaging chemical (which would take a true anti-perspirant) or neutralize the chemical.