First I would like to thank you for the jewelry photography
tips. I have a casting problem. I have to deliver some 18k white
gold cast pieces in a week. I’ve done it before using a 75%Au and
25%Pd alloy. It’s very difficult, it wouldn’t work in
gravity/vacumm so I had to reassemble my centrifugal casting
machine and even though didn’t come up with something
satisfactory. I can’t buy any alloy here and can’t order from
any supplier because it wouldn’t get here in time. I found four
different alloys in books, all of them have Copper, Zinc and
Niquel in different amounts. I don’t have much time for
experiences right now. I wonder if I could add a little Tin to
lower the melting point. I can’t use the centrifugal machine any
more, I don’t have space.
Dear georgeDebbie, Interesting about the alloys hot is so
important.. Where would one buy Zinc (is it toxic or ??) to
add to your alloys.. Is it really needed...What does it do to
yourm alloys?? When I make 14k white gold I just take half and
half and it seems to work well??calgang (orchid)
hi calgang, all metal gives off fumes when melting. zinc having
the lowest melting temp in casting alloys is the first to burn
away, it actually evaporates. i don’t know exactly how toxic it
is, but i imagine it is less toxic than cadmium. i’ve discussed
before why zinc is added to alloys in an earlier post about 2
months ago. it absorbs oxygen and prevents some oxydation, it
acts as a grain refiner, it increases the interval between
solidus and liquidus, when rolling, it increases brittleness, it
makes it more difficult to fuse than yellow trinary alloys. it
also lowers the liquidus. so you see it has advantages and
disadvantages. i don’t think it is indispensible. one could
eliminate it altogether in yellow gold. i’m not sure about white
though.
when you make white gold alloy(i confess i buy mine from pm west #41, i haven’t gotten around to asking what they put in it, but
i would bet it is higher in nickel than most with a little
palladium because it takes soooo much heat to alloy it with the
fine gold. it makes a VERY whit karat gold)for 14k or 18k you
should ask yourself : what am i using the alloy for? if
structural strength is required, use a nickel base alloy. i fyou
are paveing or using it for prongs, you may want to use
palladium base alloy. what i mean by ‘base’ is mostly made up of
that alloy. withe gold alloy( the metals that make up the
alloy, not the gold) melts at a significantly higher temp than
the actual karat gold alloy, so you better have the torch muscle
to melt nickel (2645f), palladium (2831f) or platinum (3224f).
in a previous post i mistakenly put silver an an ingrediant for
white gold, it isn’t. zninc in white gold usually doesn’t
usually exceed 9% of the total karat gold. here are a few
recipes for 14k white alloyused in casting: 22.1% copper,10.8%
nickel, 8.77 zinc, .5833 in gold. for all purpose: 23.5% copper,
12.2%nickel, 5.97% zinc .583 in gold. for 18k white: 75 gold 25
palladium or platinum or 75 gold, 10 nickel, 10 palladium and 5
zinc. use those fused silica crucibles if you are melting
nickel, palladium, or platinum. there are other recipes. the
only ones i’ve made myself are the 18k palladium ones. i’m just
about ready to beef up my melting capabilities with hydrogen as
fuel instead of propane. i could go on further but it is late
and i’m a little tired of typing. best regards,
geo fox
Ps if you wnat to buy zinc, most metal suppliers have it.
Browsing my books I found the following alloys: gold 750/-,
palladium 150/-, copper/nickel 100/-; gold 750/-, silver 105/-,
palladium 100/-, copper/nickel 45/-. Melting ranges are given
with 1150 C - 1095 C for the first one, 1150 C - 1020 C for the
second, this one being only half as hard (95HV) as the first
(180HV). The first one is said to be better suited for casting.
I’d avoid tin, as it results in compounds that have very low
melting ranges (around 500 C) and make the metal hard and
extremely brittle, especially with metals of the platinum group.
Gold can take only up to 4% tin without the forming of tin
oxides that segregate at grain borders and make the alloy
brittle.