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Red gold alloy - Double Metal Casting


#1
I need to make a ring for a client which has a platinum center and
a RED gold part which will be cast around it.  David Barzilay. 

Dear David and All, I do not write this to give advice but to ask
as I am very interested in this technique.
Unfortunately, I have not much about it. There is a short
explanation on ‘Double Metal Casting’ in Practical Casting and an
even shorter one on ‘Implants in The Complete Metalsmith’ (both from
Tim McCreight). I read this over and over, but I still do not
understand how I can manage to build a support that will keep the
metal (center ring, bezel, inlay piece, …) where I want it to be
after the wax has burned out. How do I construct the ‘finger of
investment’ that grips the implant into place (but this means
altering the design)? Or, as McCreight writes, sometimes an extension
has to be soldered to lock the piece in position (of course, any
extension makes the implant heavier, and increases the risk that it
will ‘sink’ into the wax). Could you - or anyone else - please explain
this?
Thank you for reading. Best regards, Will


#2

Will, If you want to cast with another metal or object already in
place (imbedded in the wax), two rules have to be observed. The
first is, obviously, that the object imbedded has to have a higher
melting point than the metal poured around it. Imbedding platinum or
steel, for example will work in a gold or silver casting. Imbedding
gold into a platinum casting will not work.

The second rule is that when the wax melts, the object imbedded has
to be held in place by the investment or in will simply drop to the
bottom of the cavity.

Let’s say that you want to imbed a platinum sphere into an 18k gold
cast disk. If the sphere is large enough to protrude through both
sides of the wax, the investment will hold it in place when the wax
melts. If it does not protrude through the wax, simply adding a
platinum wire to the sphere will hold the sphere in place by
projecting into the investment. The wire can go through the wax and
project into the back side of the casting, or it can project out the
front. Having it go through the wax will often anchor the sphere
into the cast metal. Having it project out the front will allow the
sphere to rotate once the gold is cast, since the two metals will
not melt into each other. This would give you a "ball and socket"
joint.

If David wanted to cast two red gold saddles onto the shank of a
platinum ring, just wrapping the wax around the platinum shank will
not create the strongest bond. I would cut some locks into the
platinum shank, either with a drill or burr, and make sure that the
wax flowed into these cavities. Since the ring shank is so large,
the investment will easily grip it. Sprue the wax as you would
normally. When you break out the casting, you will find the red gold
has cast around the platinum and is held in place by the mechanical
connection of the locks. If you want a seamless connection, you will
probably have to add solder to the joint. And, since platinum does
not oxidize when heated, the pre-polished platinum ring needs only
the finish on the red gold to be complete.

One of the most basic projects you can do with this technique is to
simply put platinum wires into a wax ring, with metal sticking right
through the wax. Cast this in gold, or silver, and you will get a
casting with platinum wires sticking out of it like a porcupine.
Just file the wires smooth to the cast surface, and you have
platinum inlay! With a little practice, you can get quite
creative…

Doug Zaruba


#3

Hello , I alloy Kt. golds myself and for strong color have often
made straight gold/copper alloy , although now I’m adding a small
amount of silver , in the 3-5% range to toughen up the alloy . The “
problem” with high coppper alloys is that they MUST be quenched
while hot , they harden so much if slowly cooled that they can break
in the flask [ so I’ve read] . If well annealed , the problem , if
any , is that the metal works like it is softer than regular yellow
range metals . I’ve seen some “over red” color in 18k italian
jewelry and have wondered about its contents . The published red/pink
alloys all show Zinc in addition to the copper and silver , perhaps
someone can inform us better about this area of gold
alloying…

Mark Clodius


#4
 If you want to cast with another metal or object already in place
(embedded in the wax), two rules have to be observed. The first is,
obviously, that the object embedded has to have a higher melting
point than the metal poured around it. 

Hi, Doug, There is no possible doubt that you know a lot more about
casting than I do, but , perhaps just the luck of the naive-- I’ve
broken this rule by casting copper into/around sterling with no
problem. Noel


#5

Noel, This is really the beauty of experimentation. When you don’t
know that it won’t work, you do it anyway…and it works! I suspect
that it works because the temperature of the molten copper is not
high enough to completely melt the silver when they make contact. I
would suspect that the two metals really bond to each other, like
granulation. In granulation, it’s the copper that alloys to the
surface of the underlying metal, creating an alloy with a slightly
lower melting point. Just a little copper is all it takes.

I would also suspect that the respective volume of each metal would
affect the success of this casting. If you tried to pour a large
volume of copper over thin silver wires, you may not be as
successful. Personally, I’d still try it, because (like life), you
never know what you’re gonna get…

Doug


#6
If you tried to pour a large volume of copper over thin silver
wires, you may not be as successful. Personally, I'd still try it,
because (like life), you never know what you're gonna get... 

Well, Doug, I totally agree. And I did cast copper around silver and
nickel wires to make dots, and it worked fine. This is a great
example of “ignorance is bliss”! The whole project was because I
screwed up a silver ring, and the thickest part didn’t fill in (one
of two sprues came loose during investing). So, play time! I filled
the space with wax, stuck some wires through and out the other side,
re-invested it, and cast in copper. I didn’t actually like the
result, but that’s another issue…

Noel