Amongst her tools was a piece of honeycomb soldering pad!
This may well have been salvaged from an automotive catalytic
converter, which is what those honeycomb ceramic things were
actually originally developed for…
I had a look at the can mixture. It looked like a brown
rubbery clay mixed with some sort of fibre. Unfortunately we
could not communicate because of the language difference!!
Probably just some bark or perhaps wadded up cloth, or
something. Doesn’t much matter, the key is that it’s wet. You
can use a wad of wet newspaper just as well.
I have three questions, does anyone know what the canned
mixture could be?
Who knows. It’s not critical to the process, only whatever was
convenient.
How would she have melted the gold in the first place on top
of the plaster investment? Granules would drop down, unless it
was a larger nugget. Is this a form of steam casting?
They key to this, which IS indeed steam casting, is that the
item to be cast is sprued with small diameter sprues, often
several of them. For us, the normally recommended way to do it
is to take your wax model, add whatever normal types of sprues
you add, but keep them short, like about 1/4 inch. top that
with a ball of wax, somewhat larger than the sprue diameter. To
the ball, now add a number of 14 guage wax wires, spaced at least
their own diameter apart, and sufficient number of them that
their total cross sectional area is at least that of your main
sprue into th object. These are then affixed to your sprue
base. After investing, use a spoon to reshape the button from
it’s conical shape to a round bottom hemishpere. The spoon will
be cutting through the 14 guage wax wires too. Don’t carve
deeper than those wires go. What you’ll end up with is a round
bottom crucible shape in the investment, with a “drain” in the
bottom formed of those multiple small holes, rather than a single
large sprue hole. The key to steam casting is that the molten
metal has sufficient surface tension that it will not drop down
such a small hole without a push. You add your solid metal in
large enough chunks so tiny bits don’t drop down the holes.
When it melts, the molten metal stays in the crucible, instead of
plugging the holes. Only when you seal the top of the crucible by
bringing down that moist can, and generating steam pressure, does
the metal then get forced down past those fine holes, into the
ball reservoir, and from there, to the sprue and model cavity.
The amazing thing about steam casting is how well it can work.
We’re so used, as western jewelers to using our high tech methods
and machines, that we are surprised at how easy casting can be
with litterally no equipment at all. My first castings, after
college, and before I could afford professional equipment, for
example, were burned out on my kitchen stove. Was a gas burner.
A clay flowerpot, lined with several layers of aluminum foil,
was placed over the flask directly on the burner, and turned on
high. several hours later, the flask was nicely burned out and
at casting temp…
Another low tech casting technology that would amaze you with
it’s simplicity and the sophistication of it’s results is the
methods used in West Africa for casting gold, bronze, etc. The
models are often just beeswax, collected directly from the bees.
Rolled into very thin wax wires, and tiny balls, these things are
then coiled into the most delicate and beautiful forms. After
the models are made, and sprued, the get “invested” in a mix of
plain old clay, and organic matter like dried grass, etc. (the
initial coat over the model is fine clay, no straw). the is
formed, with successive layers, to form a mold, and the end of
the sprue is built up into a crucible shape as well. After the
clay has thoroughly dried, this thing is placed in a fire
(charcoal) and the wax burned out. It’s cooled slowly, and the
casting metal is placed in that open crucible shape, and more
clay is then built up over it to close the cavity. You end up
with a dumbell shape, one end of which is a hollow cavity with
the casting metal enclosed, and the other end is the model
cavity, the two connected by a sprue. Sounds complated, but do
keep in mind that so far, all the casting materials are dug
either from a beehive, or from the ground, except perhaps the
metal, and that too, I guess… Anyway, now this thing, after
again drying the clay, is placed again in the fire, this time
with the metal containing end down. The straw/organic content of
the clay makes the mold porous enough to allow fumes to exit, as
well as providing a nice reducing atmosphere for the melting
metal. When the metal is melted, judged by the color of fumes and
flames surrounding the mold, the whole dumbell is simply
inverted. The molten metal runs down into the mold area by
gravity alone. A look through any of the texts showing the
historical Ashante cast gold and bronze work will demonstrate
just how well this technology works. The reducing nature of the
mold keeps metal cleaner than our normal investing procedures,
and the high metal and mold temps allow a complete fill even with
fine sprues and very delicate filigree models. Some of these
things would be a real challenge to cast consistently using our
normal methods…
Hope this helps.
Peter Rowe
Peter Rowe