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I too have had good results using ammonia/H2O2 on arsenical copper with 20%+ As. Be sure to read the instructions carefully - a common mistake is to use 3% H2O2 rather than the 30% specified - and to use fresh H2O2, since it deteriorates rapidly if not stored under refrigeration. Apply with a clean cotton swab or by holding the inverted sample upside down in the etchant, using the gas evolved by the reaction for agitation. I seem to get better results with the latter method. For low-alloy coppers, which are much softer, the best way (in my experience) to obtain a scratch-free,etched finish is to do final polishing(after preparation to 1 micron with diamond paste)on a vibropolisher with colloidal silica solution - I use Buehler's, but Struers makes a comparable product. To etch and polish simultaneously I add a very small amount of ammonium persulphate to the colloidal silica - about 0.1 g to 100 ml. Use a long-napped cloth (e.g. Buehler Microcloth). The rate of attack is sensitive to both the concentration of the persulphate and to the applied pressure. I apply weights to the samples so that the gross weight of a 1" diameter sample is 35-40 g (excuse the mixed metrics!) and 70-75 g for a 1.25" diameter sample. Polishing time is 30-45 minutes. Colloidal silica is very hard to remove once dry, so samples must be gently but thoroughly wiped with a CLEAN cotton swab under running water immediately after removal from the vibropolisher. This seems to work well for most samples, especially native and other very pure coppers, and for brasses, but there are always some samples that don't etch fully. I etch these with ammonia/H202 afterwards. ---------------------- David Killick Associate Professor, Department of Anthropology, University of Arizona, Tucson, AZ 85721-0030. Phones: office (520)621-8685; laboratory 621-7986; fax 621-2088 [log in to unmask] %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%