I’ve been trying to alloy some gold for experimenting with
reticulation. I’m using a 25/75 copper/gold alloy. I think I
have a pretty good understanding of the reticulation process,
but as I began to mill the alloy into sheet and anneal it, I
started running into problems with the metal cracking at the
edges easily. I started wondering if I am starting to form some
of the copper oxides beneath the surface as I anneal the metal
between rollings, which might be causing brittleness which leads
to the cracking at the edges.
Is there anything special I should be doing to this alloy when
annealing it (e.g. fluxing it, using a reducing flame, etc.)?
Westford, MA USA
Alan, the specific red gold alloy you’re using, 18K red with
only copper, is subject to an anomaly that can form when the
alloy is heated, then cooled too slowly through the 700-900 F
temperature range. It forms an ordered array structure, rather
than the desired random mix of gold and copper attoms. This
structure is brittle and cracky. You avoid it when working with
this alloy be quenching after annealing, when the metal is just
barely below the point of glowing. don’t wait longer than that.
It MUST cool quickly through that critical temperature range.
Many workers recommend quenching these alloys (rose golds) in
alcohol instead of water. Both work, for the quench. Alcohol
will chill the metal slightly more slowly, so presents a bit less
shock, and it will tend to reduce oxide and fire scale on the
surface. A little… If you use a gold copper alloy of higher
than about 20 K, or lower than about 16 K, you’ll not have so
many problems. Or, if you add just a bit of silver, you also
disrupt that formation of an ordered array on slow cooling…
The other thing to be aware of, is that in addition to the
ordered array problem with 18K gold/copper, you also have to
contend with age hardeneing of rose gold alloys. Slow cooling
will cause precipitation or age hardening. Not that much if it’s
not cooling too slow, but still sometimes enough to cause
rolling to be more difficult. Again, the answer is to quench
after annealing. Be sure, also, that you’re anneal temp is only
to a low dark red heat. Overheating will also contribute to
weakness in the metal, due to excessive grain growth.
As long as the cracking doesn’t extend too far into the piece
why not incorporate it into the design? Sometimes the cracks
will fill when you heat it for reticulating anyway.
Borax added to the alcohol will stop fire scale and give cleaner
work. John the Ringman