whitemetal casting for the dome isn't the best I've ever seen but it can be made good. Luckily a spigot is cast in the bottom and this can be fitted in a chuck which in turn fits into an electric screwdriver. Don't use a power drill for this if you are trying the same thing - the screwdriver, being slower, is much more finger friendly.
Rotating the dome I cleaned the surface with some flexible grit stuff. Then the metal is given a good polish using some Brasso wadding. This always brings whitemetal to a nice shine. I think it looks like pewter rather than a lead based alloy. Whatever, this is a job worth doing and hopefully will result in a top quality finish once painted.