[Enamel Bits] Why to treat copper with a base before enameling?

Eddie, in the thread: “Slime Pickle and Pool Supplies” you mentioned
that you are a chemist. Thus I am hoping that you might be able to
explain why enamelists are supposed to treat copper with a base before
enameling it. What difference would it make to the metal? Would there
be a surface layer of OH’s? If so what is the advantage when
presumably all that soon disappears with the intense heat.

Is if folk lore or logical?