Thanks for your kind reply Leonid!
How about pouring temperature?
Metal should be hot enough to completely fill mold before starting
to set. 3 ounces of gold would require 200 degree plus over alloy
liquidus, and that with pre-heated mold.
I did it just as you said.
Mold size is another variable to take a loot at.
Ideally, metal should completely fill the mold. If filled only
partially, unfilled part becomes heat drain and that results in
ingot stress, which would lead to cracking.
I use an open ingot mold, those in which the ingot forms
horizontally, and as I used only 10gr of alloyed gold obviously the
metal didn’t fill the mold completely, but the ingot was very even
Ingot should not bent or become wavy during rolling. If it is, it
may indicate unevenness of ingot grain, or problems with mill
Ingot is more likely candidate so anneal it and forge again.
Forging must achieve at least 30% reduction in thickness to be
effective. If problem persist than mill examination is in order.
I forged the ingot too, but not to a 30% thickness, I’ll try that.
The ingot DID become wavy, but it happened when I milled it with a
very slight compression and without annealing until 50%-60%
reduction. I thought that the “Wavy” form was a problem, so I did all
the melting again and milled it with a somewhat stronger pressure and
the “wavy” problem was gone.
If nothing of the above will help, that assumption of chemically
good alloy, should be reviewed.
Well, to be honest, as I waited for some response, I did some
further experiments, and I was actually able to mill the ingot! I
milled it with a cycle of, let’s say, three passes through the mill,
each pass of 0,05mm compression, and then annealed it. As you can
imagine it is quite annoying to anneal that often and THAT much, but
it was the only way to do the work. I have the ring almost done now,
but anyway, I would like to understand what the problem was, so the
next time I can do it the right way.
If you describe alloy composition and methodology of smelting, we
can discuss it further.
The alloy was 7,5gr gold 24K + 1,2gr pure Silver + 1,3gr pure Copper
(I always like to add a little more copper since I love when the
gold has some yellow/orange color). I melted the 3 metals at the same
time in a crucible which was used only once with 18K gold alloyed by
me too. To assure a good mix I heated the metals to a very bright
yellow color as I stirred the mix, I poured it in the mold and waited
until it was cold, then I melted the gold again but this time not
that hot, I think it was 100deg to 200deg above melting point, then
poured it, and the rest is history: Cracking!
Thanks for your time, I’ll check your site as you suggested me.