Right, I've done the vinegar-and-water acid etch trick. I can certainly see a difference; the pattern is very distinct, with many swirls and whorls, and even appears to have a tiny bit of a texture to it - though I can't feel anything through latex gloves. I've taken five pics and I hope they've come out all right, but if not, I'll work on getting some more done.
Incidentally, any tips and tricks on rust removal? I've not yet really embarked on de-rusting the barrel, since it seemed pointless when I was about to apply acid and water to it anyway, but hopefully I can now move onto that stage. So far I've tried a small area, using some reasonably fine glass paper, which seemed to produce results. With the lock, I've restricted myself to 3-in-1 oil and a soft cloth, removing as much excess oil as possible and leaving only a small amount as a film to inhibit further corrosion.
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