A little trick I've used for years is to use oils mixed with sintered metal powder for the basic iron, brass, copper
so forth and then gently burnish with a little graphite powder afterwards to enhance the specularity. Admittedly
it's a bit stone-age and it would probably be easier to use any of the 'Liquid Leaf'' metallics and then do the graphite
thing when it's dry. The trick is to be gentle with the burnishing.