An excellent de-bubbler (to enable the bubbles to slip off the wax)
is a 50/1 solution of ordinary washing up liquid. It works for me!
I'm also really careful as to how I mix the plaster. I mix slowly,
trying not to include any air, and use BOILED cold water instead of
regular tap water.
These days I have a vacuum casting unit but I got really good results
in my youthful days using a potato and a small tin can!
Tony Konrath Gold and Stone www.goldandstone.com