i tryed to make H2S gas with thioacetamide, heated the thioacetamide up with water added to the thioacetamide in a test tube with a cap on test tube with a hose running from test tube to another jar that the coin was in. i let the coin set in that jar for 24 hours, i also heated the test tube up intil all the thioacetamide was gone. but it didn't change the silver coin. i also tryed to make H2S gas with black salt and a drain cleaner called the works because it has alot of hydrochloric acid in it. but it made my coin black. the hydrochloric acid pitted the silver. the next thing i want to try is sodium sulfide with another type of acid to make the H2S gas. i need a acid that wont pit the silver when i turn it into a vapor gas. if you know a acid that i can mix with sodium sulfide to make H2S gas that isn't like hydrochloric acid. but there aging I'm getting what colors i like with anodizing with different chemicals i found to use with it.