Mike wrote:My cop buddies at local DMV shop tell me they have chemicals that will bring out original numbers... save for those that have been significantly heated. Mike
Don't believe everything cops tell ya. Your cop buddies are just regurgitating what cops have been telling people for years (it's nothing more than a "hopeful" deterrent to try and put the fear of getting caught into would be criminals.
Reality is: There is no chemical that can pull up old numbers on cases, IF they have been ground down more than .004" past the depth of the original stamp. I've heard that since the 80's.
I think they are referring to the VIN numbers stamped on those thin aluminum or brass data plates that are about 1/16" thick.
Here is the abstract report on bringing back old numbers using reagents
A study has been made of the characteristics of restoration of obliterated engraved marks on aluminium surfaces by etching technique. By etching different reagents on 0.61 mm (.024") thick sheets of aluminium (99 wt%) on which some engraved marks had been erased to different depths it was found that the reagent 60% hydrochloric acid and 40% sodium hydroxide on alternate swabbing on the surfaces was found to be the most sensitive one for these metal surfaces.
This reagent was able to restore marks in the above plates erased down to 0.04 mm (.0015" or 1½ thou) below the bottom of the engraving. The marks also presented excellent contrast with the background. This reagent was further experimented with similar aluminium surfaces, but of relatively greater thickness of 1.5 mm (059"). It was noticed that the recovery depth increased slightly to 0.06 mm (.002"); this suggested the dependence of recovery depth on the thickness of the sheet metal.
Further, the depth of restoration decreased in cases where the original number was erased and over which a new number was engraved; the latter results are similar to those of steel surfaces reported earlier [M.A.M. Zaili, R. Kuppuswamy, H. Harun, Restoration of engraved marks on steel surfaces by etching technique, Forensic Sci. Int. 171 (2007) 27–32].
So as long as the "artist" has ground the boss or case bottoms down at least .004" past the bottom depth of the original stamp, there is no way to pull up an old VIN, especially if another number has been stamped over it or impossible if the VIN has been welded over.
I have some old junk (severely broken) case halves and I have both chemicals on hand (hydrochloric acid, for cleaning particulates out of my parkerizing solution) and sodium hydroxide (for removing all organic matter from pot metal carb bodies before chromating them), Maybe I can do this experiment my self !!!!