[zapokee]

Originally Posted by CTech

There are a number of acidic etches that might work on 306L stainless steel to reveal a stamped serial number, but I don't know if they would be effective on an engraved serial number. I've never used them on a watch case but I have some experience with them in an industrial setting to look at discrepancies in the structure of various metals.

The big downside of all of them is the surface preparation required before the application of the etch, and a lot of them will not reveal anything unless the surface has been polished to a mirror finish.

There are many proprietary etches such as Fry's reagent, Turner's reagent, Davis reagent, etc. and a lot of these contain ferric chloride in dilute hydrochloric or phosphoric acid. There are also many recipes for similar etches published on the web so you could in theory mix your own.

Some experimentation is usually required to get good results and it is very rare that the first etch used gives good results.

Of the other techniques available, it might be worth trying some of the magnetic particle crack detection materials such as Magnaflux or Mi-Glow, but I don't think 306L stainless steel is magnetic enough to allow these to work effectively.

The best technique for revealing obliterated (stamped) serial numbers on weapons is backscatter diffraction electron microscopy but this is prohibitively expensive and I doubt if there is any information about using it on engraved numbers.

If you want to take this further and talk to professional metallurgists about it you need to tell them that you are interested in revealing engraved numbers in 306L stainless steel as they might only have previous experience with stamped ID marks, and the techniques used will be different.

In short, I might investigate some of the magnetic particle materials a little bit, mostly because they are cheap, non-destructive and relatively easy, and if that didn't work I would then probably ask for help from a professional or academic metallurgist before going further.

What a brilliant response on possibly the most niche area of expertise ever . That's why this forum is awesome.