Different folks will give you very different advice. Some will tell
you to oil the mold and heat it until it smokes. Others will tell you
that this is madness. You must carefully clean any trace of oil or
grease from the mold and lubricate it with soot from a flame. I’ve
tried both and find that oil is not only cleaner and easier to deal
with, it works better for me. I use “3-in-One” oil, but any light
machine oil works just fine.
The constants that both camps seem to agree on are that the mold
should be heated to somewhere around 700 degrees F (for silver and
yellow gold, a bit higher for white gold), and the pour should be
one, smooth movement with the metal aimed to the center of the hole
so that it’s not poured down the side.
Another disagreement exists concerning how best to prepare the ingot
for rolling or drawing. Some say that you should forge it first;
others will say this is a waste of time. I have found forging prior
to rolling to be beneficial for silver and yellow gold alloys and
mandatory for rose and white golds. By forging, what I mean is
actually distorting it pretty heavily, not just giving it a few
whacks with a hammer.
This is one of those things that really illustrates the truth about
most things we metalsmiths do: whatever works best for you is the
best way for you to do it.
Hope this is helpful.