My favorite is Radio Shack printed circuit etchant, which is sold in pint bottles for a few dollars. It is a ferric chloride solution, completely harmless to glass and--I think--to fingers, although it is dark brown and may stain sinks and containers.
Aart M. Olsen aart@uiuc.edu 217-333-7467 College of Veterinary Medicine Univ of Illinois at Urbana-Champaign