The following is from Dr Gaddy (after a long discussion)--hope it helps....
The use of ferric chloride (circuit board etching--very diluted) is used to remove the browning/black from bbls from one of the steels after they have been rust blued.
The sulfuric acid is a quick method to enhance the pattern, but removes significant amounts of metal. It is often used on knife blades but doesn't have much durability.
The use of a chemical (if forget the type) used to etch galvanized metal before painting is effective in seeing the pattern. Chemical may be found at any paint store.
Both the sulfuric acid method and galvanized metal prep produced a negative pattern enhancement whereby the ferric chloride/bbl blacking produced a positive pattern.
Hope this helps. Dr. Gaddy was a true gem and had thousands of tricks that only experience would highlight.
Dan
