@clubman might know how these were done. I think they were probably enamelled originally and he knows a thing or two about proper enamelling.
Application of the colour might have been done a bit like tampo, rolled on with a squeegee and maybe the excess scraped off if done by hand. Then oven cured which flows it out evenly on the surface. Polished up at the end. Just speculating though, I don’t actually know.
I’ve always felt that brass headbadges must have been quite an expensive item to put on a frame. First a set of stamps would have been made up to cut the shape out and then press the features into the badge, then the colouring, curing and polishing. It’s quite a lot of work!