Zinc-silver master alloy

Hello,

In making a zinc-silver master alloy, I melted the gold first,
then the zinc to avoid the zinc from tarnishing quickly in molten
metal. However, after adding the zinc to the silver and allowing it
to solidify, there are micro bubbles throughout the surface.

How did this happen? How to solve it?

Has anyone ever tried mixing silver powder with nickel (or any
other white metals, like pladium or platinum) powder together and
then melting them together at a time?

Thanks to whoever that can help.

Yong Tze Shoong.