I was given a 1920s? Limit pocket watch in very poor condition a few days ago. The case back was very badly rusted with deep pitting. Someone on here advised me that the case was originally blued gunmetal, so I thought I'd see what was possible with it, to make it not quite so bad at least! Heat bluing seemed out, as the hinge looks to be brazed in place & I did not want to risk it falling apart!   I got a bottle of "Jenolite gun blue" to try. First, I sanded the back to