Not so much a 'How To' as a time saver that has helped me. VHT Caliper paint... It's remarkably tough and I've been using it to paint all the little metal items on my 620. I even use it on nuts and bolts and it doesn't chip off when you put a wrench on it. I sprayed some hand tools and the paint has held up well to being banged and dropped.
I sand blast the parts, paint and then bake in an old toaster oven at 250 deg F for an hour. I find that the time to blast, paint (drys fast - like 10 min fast), bake and cool is faster than regular spray paint. And is very resistant to brake fluid. No more waiting over night for things to dry.
I stumbled upon this tip at Sierra Specialty Automotive. They sleeve master cylinders, or used to, the gent that runs it is now retired. However the website is still up
Here is the paint tip from Sierra Specialty Automotive just in case the site ever goes down.
Can I paint my cylinders?
Yes. Glycol brake fluid is an extremely effective paint remover, however, so regular paints cannot be used. Most two-part (catalyzed) paints are resistant to brake fluid, but one-part paints such as spray paints are not. Some of the conversion coatings sold to restorers are resistant to brake fluid. POR-15 is one such coating. Note that some colors of these coatings may not be resistant, so ask your dealer. If you're going to paint your cylinder, we ask that you let us do the sleeving first. Be sure the painter masks or plugs all surfaces and ports that will be exposed to brake fluid or covered by rubber boots or gaskets.
We use VHT Brake Caliper, Drum, and Rotor paint with good results. Start with a clean casting, mask gasket surfaces and plug ports, apply two thin coats per the instructions on the can, allow to dry overnight, then cure in an oven. The VHT website recommendation was originally 350 degrees for 1/2 hour and was later changed to 200 degrees for an hour, but we find that's not quite hot enough to effect a full cure. We are having very good luck curing at 250 degrees for one hour. There is minimal odor since most of the volatiles go away during the air-dry, so you can do it in the kitchen without triggering a divorce. From our experience, one can will do about four typical master cylinders. It makes a very tough coating that is very resistant to brake fluid. Most original master cylinders were bare metal, so the Cast Aluminum paint is probably most "correct" although it is quite a bit brighter than cast iron. Our personal preference is the Satin Black color. We try to keep all the colors in stock, and we will paint and bake your cylinder for $25 if you prefer not to do it yourself.