I have a very similar one, it has a varnished plain brass fount but has silver paint underneath so that was probably the origial colour. Black knob and black ventilator cap.
The original font that came with this had silver paint, but was contaminated inside with god knows what, I have cleaned most of it out, the inside now looks like it has gray tarnish all over it. so will deal with that later.
I rubbed an M1 down in the Autumn. Back to brass and used Hammerite 5084785 Metal Paint: Smooth Silver. It is a good match for the silver fonts. I used Hycote XUK435 Petrol Resistant Lacquer Spray. I believe all M1s were silver. This is before Couple of during: and nearly finished (collar and glass not cleaned yet): but you can see the silver came out well to its original state.
Nice finish, The silver finish on my tank isn't to bad it's the inside that's the problem, I'll try and get the inside back to brass or use it to in an electric conversion (without damaging the tank, cable going in via filler cap).
@mauld Have you tried caustic soda solution ? - I have used this on very dirty tanks. It gets hot and the gas is not clever so it's a back garden job
I managed to get the gunk out, but now it is like tarnished brass all grey inside, I thought about boiling it in bicarbonate of soda or citric acid but not sure how that will effect the brass. Costic Soda sounds a good recommendation, any details on the process i.e diluted/neat, time it takes, rinsing. I'm working on my second M1 (21c) at the moment, the tank can wait, there no rush.
I used quite a concentrated solution made from crystals in a pyrex jug - so much so that it got hot enough to burn skin through the tank. I left it there for two hours. I think it could have been weaker and still do the job. The solution did not affect the brass and soldering. It did damage paint. The stuff that came out was amazing. I just rinsed it four times with fresh water and let it dry out over the boiler. I have been using that tank for a couple of years now. However I now know that caustic soda can make brass go brittle so I would use a weaker solution for a shorter time. It also dissolves aluminium.
A nice job you are doing there. The silver paint look good. Not sure if kettle de scaler would help clear your fount. Good luck with your project.
