I’ve got a recent problem that I’m hoping you can help me trouble
shoot. For over 16 years, I’ve alloyed my own 18K and worked from
ingot for most of my work. Recently I started working with sterling
silver and for some reason, have encountered a wall that I just
cannot seem to find my way around.
I’ve been using a standard reversible ingot mold and attempting to
make flat ingots for sheet. The problem is that no matter what I
try, my ingots (a little over an ounce) end up with a whole bunch of
little fissures after about 2 or 3 passes through the mill. Though
they sometimes occur in multiple places around the ingot, they
pretty much ALWAYS appear in the center of the bottom half for some
reason. I have scoured all my books, the forums, the internet in
general and cannot seem to find an answer to this problem.
What I’ve thought and what I’ve tried:
Contamination: I’ve eliminated possible contamination by starting
with fresh sterling (alloyed myself from .999 silver and copper)
along with a new crucible. I doubt contamination though because of
the consistency with the location of the fissures. If it was a
problem with the alloy it should either be throughout the ingot or
at least move around each time I re-pour it.
Perhaps the ingot is cooling too fast or too slow resulting in
either shrinkage-based weakness or large crystalline structure? I’ve
tried a cold mold, warm, and hot with no effect on the occurrence of
the fissures. I’ve also tried annealing the ingot immediately after
the pour before forging to see if that helps. Nope!
Melt temperature too high: I’ve tried pouring just after being
liquid enough (resulting in incomplete ingots), just a bit after
this stage resulting in complete ingots with a few bubbles trapped,
and finally high temperature pours which result in complete ingots,
but with large crystalline patterns on the surface.
Sterling not properly annealed/worked prior to rolling: I’ve
forged the ingots (cross-peen and 45 degrees left and right to
rolling mill direction on both sides of ingot). I’ve tried
potentially under-annealing and over-annealing to no alteration of
the occurrence of the cracking. For the heck of it, I’ve also tried
rolling just after pouring (no forging) which changed nothing for
Quenching too soon or too late: I’ve tried quenching immediately
after annealing, giving it a minute to air cool before quenching,
giving it 5 minutes before quenching, and finally letting it air
cool. No change in occurrence.
Too turbulent of a pour: I’ve tried pouring slowly, quickly,
medium. They pretty much all have the same result. My last and only
idea left is to try tilting the ingot mold a bit to have the silver
roll down the inside rather than splashing directly on the bottom
from the top.
For the life of me, I cannot seem to figure out what exactly the
problem is and am pretty much out of things I can think of to try.
What bugs me more than anything is that because the fissures occur
in a consistent spot, it’s got to be something I’m doing or can
control and not the alloy, but after spending the last 2 days and
pouring about 50 variants to attempt to correct the problem, I’m
just stumped. I’ve never had this problem in 16 years of pouring and
rolling 18K gold ingots, but for some reason, sterling has decided
to become my bane.
Has anyone encountered this problem before or have any
thoughts/insights on what I may have overlooked?
Many thanks for help you can offer!