I recently cast some brass medallions, the finished items had
surface pitting, the process was lost wax casting, I did the burnout
with a batch of rings which were cast in Sterling Silver, all the
sterling silver items cast perfectly.
When I melted the brass a thick yellow smoke issued from the melt, I
think maybe the zinc burned out causing the problem. The brass used
was new brass rod, no rubbish in the melt, any advice re flux etc
would be appreciated.