How do I make casting grain?

I’ve got a big ingot of bronze I’d like to convert to casting grain.
I know silver and other metals don’t like to be remelted, and don’t
cast well if they have been melted before.

I’ve done the hot metal into the bucket thing for pewter, a long time
ago. Are there any additives I need for bronze, silver, etc…or,
any other considerations?

How do the big manufacturers make grain? Thanks!