Etching Metal

I had a play day with Susan Chong yesterday where we used a lot of the Ten Seconds studio metal products that we have. I had wanted to try my hand at metal etching using Stephanie Lee's book, Semiprecious Salvage for my inspiration. I followed her directions for etching metal; I used copper and ferric acid; yet after waiting the allotted time, I found my metal had totally dissolved in the acid solution. Too thin of copper?? I have emailed Stephanie to see if she knows. It was kind of freaky working with a product that totally dissolved copper! And then to find hours later after golfing that I had somehow gotten a bit of the acid on the bottom of my toes! I was extremely relieved to see that the skin wasn't eaten away!! Now to pray that I don't have poison in my system.... the trials and tribulations of being an artist! I think I need to stick with safer mediums!