hi all, some time ago i asked about an alloy called 'pure gold’
and told everyone that i would share my experience working with
pure gold is available in two options, both are .9985 pure gold:
alloy ‘a’ and alloy ‘c’.
alloy A is meant for fabrication and/or casting under vacuum.
one can achieve greater hardness with it than alloy C. i’ve
fabricated comfort fit bands with this alloy and it does indeed
get very hard after work hardening (no great hardening occurs
during working) then age hardening for about 3 hours (at 300C).
exactly how much harder alloy A is than alloy C, i don’t know
because the info suppplied only says 180 hv and does not
specify. 180 hv is the hardness for annealed 18k yellow, but
alloy A seems much harder than this to me.
the comfort fit bands using alloy A is a very successful
i chose alloy C for a casting project. it is supposed to yield
harder results when only age hardening can be utilised. i cast
with a torch in air even though i was warned this could be
tricky. casting in air with induction or resistance melting is
reccommended. when i melted alloy C it developed a heavy dark
skin as soon as the metal started to slump that seemed to get
thicker the longer the alloy was melted. the sparks that fly
when one is burning off alloys (over heating metal) were evident
so i let the casting arm fly, hoping for the best. it was very
hard to tell if the charge was completely molten or not. i let
the flask cool without quenching. looking into the crucible there
was a small amount of the casting charge clinging to the walls
indicating the charge was not hot enough. once removed the
casting was a good fill but with a few cracks ( indicating that
the alloy was too hot, go figure)which were repaired with 21k
solder. the button was concave, indicating too hot metal.
i assume that the metal was too hot and the leftover metal in
the crucible was due to the less viscuous ‘skin’.
when discussing the cracks with the supplier he said it was
common when the metal went from too thick to too thin (from sprue
to model, 8g to 18g) and within the model ( which was a pierced
filligree ring about 1mm x 5mm).
one must use platinum type investments and crucibles.
i would deem the casting project with alloy C moderately
successful. the results were not as hard as the fabricated piece
with alloy C. nor was it without a few learning curve mistakes.
the finished jewelry piece was certainly acceptable, but not
pristine due to the repaired cracks.
when i am required to cast an object in either alloy i will be
certain be able to cast under vacuum or cover gas and without a
torch (or send it out to someone who does).
any process without melting is pretty straightforward and yields
the alloys are supplied in 8mm rods so one can roll them into
anything one desires.
the supplier : puregold, phone 510.262.0364. they were very
helpful and patient with my many phone calls and questions.