None....Its rough cast alloy,and it will be blasted so the bond will be good. Hammered finish paints generally dont require a primer.
If you like you can give it a light etch prime or often most blasters do it for you.
And importantly...NO grubby fingers or oil and dirt should be allowed to touch the metal after blasting. Pick it up and wrap it up till your ready to paint.
Blow off all the fine dust,prepsol re blow and a light dry with a heat gun helps.
Then Paint away....light coats, then a heavier coat to bring out the hammered look.
And NO puncturing cans!!!!!!
