A friend of mine has a number of old firearms and asked if I would have a go at the hot bluing process for him, so yesterday I mixed up a small scale amount of salts from the simplest recipe I found online (5lb sodium hydroxide, 2.5lb potassium nitrate, 1gal water, I actually used potassium hydroxide because I have it on hand) and ran a couple of test pieces.

The first was a newer looking P&N HHS drill bit that took the blue quiet well considering the only prep work I did was wipe it down with some metho.

The second test was a piece of hot rolled mild steel I turned and polished up, it came out a little bit blotchy at one end, I suspect the caused was while I was bluing some water evaporated from the salt mix exposing areas of the part to air, I also noticed the galvanised tie wire I used to hang the part left a mark so I'll have to use something else from now on.

The area where the blue took is perfect, I couldn't ask for better, I just need to get it even over the whole part.
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