I am working on an 18k rose gold ring. It was cast but still needs
to be hammered for design and stretched a full size. Some people
told me I should do the work cold to avoid fractures others have
told me to anneal it. Quench it in water, alcohol and oil. ANy
advice.
18K rose gold, especially the redder versions with pretty much just
gold and copper, are subject to an unusual behavior where, if the
alloy is cooled too slowly through around the 750F range, it can form
a layered structure with layers of copper and gold atoms alternating,
rather than the usual cubic crystal structure. This “ordered array”
structure is highly brittle. An item in this alloy, where that
structure has formed, can litterally shatter if just dropped on the
floor, much less actually worked in any way. Castings, if quenched
after they’ve cooled a bit, often are harder because of this
structure having formed, so the raw castings must be annealed
properly to ensure good workability. And the metal needs to be cooled
quickly enough from annealing temperature so as to not allow the
metal enough time to form an ordered array structure. Usually, this
means quenching. However, quenching rose golds from the annealing
temps in water, can sometimes be too much for the metal, leading to
stress cracks from the quenching. So a somewhat more gentle quench is
useful. The traditional answer is to quench rose golds in alcohol,
rather than water. The alcohol more easily forms a vapor layer around
the hot metal (water does this too, initially), and that layer stays
there longer, so the finaly quench when liquid actually wets the
metal occurs at a lower temp. Be careful not to have flame near the
alchol, of course, and quickly and fully immerse the gold, so there’s
not hot ignition source at the alcohol/air interface. Done that way,
it’s safe. Be sure the alcohol is in an appropriat container (not
plastic), with a lid that can be put on it if by chance it should
ignite.
Properly annealed, rose golds are wonderfully workable. And if you
like, once completed, heat treating to precipitation harden the metal
can produce amazingly hard metal, in part because some of the
hardening is due to that ordered array structure forming in small
areas. The main thing with annealing though, is not to neglect it. If
the metal starts out hard (a slowly cooled item or casting), then any
working can cause tiny cracks, if not obvious ones. These then are
not healed by subsequent annealing, so it’s important to prevent
their forming in the first place, by not working the metal at all
before annealing it. If small cracks are allowed to form at any
stage, then further working will make them show up as defects in the
item, or maybe even allow them to destroy the item. So yes, anneal
rose golds.
By the way, if alcohol as a quench is not something you’re
comfortable with, you can also quench the hot metal with a blast of
compressed air, if you’ve got a compressor handy. Cools the metal the
same as a torch flame heats it…
hope this helps.
Peter Rowe