Making hollow designs for casting

Hi – Could someone please explain whether and how hollow
designs can be cast in one piece? I’ve been reading a number of
books on casting, mainly because I want to make my waxes easier
to sprue and cast when I send them to the casting people (I
don’t plan to cast them myself). I also would like to make one
piece hollow designs. The authors talk about using a low
melting point wax in the center of the piece so that it will
burn out more quickly than the rest. I haven’t been able to
visualize how this would work. When the metal is forced in
under pressure, wouldn’t the walls collapse if the piece were
hollow? ( I once took an elementary casting course, so I have
some idea of how the process works. I actually cast a few pieces
myself. Which all seems to add to my confusion.) Many thanks!! Sandra

investing casting will be at a hotter than normal temp this wax is
available at most jewellers supplies chris

Instead of casting have you ever thought to try hydraulic press,
you cut a die and can make two halves that fit together.
just a thought thanks Amanda

Elegantbee, One of two ways on how to get a hollow piece. #1 make
a piece and horizontally mirror it (cad/cam). #2 electroform,
which is like plating but gold actually attaches itself to the
electrode. The second method is pretty much how the big guys make
stuff, the first method is for short run production, like me the
small trade shop. I have a cad/cam system where I design my
pieces on the computer and if I need to make a set of earrings or
a hollow piece, I just program my computer do the duplicate
mirrored image. When its molded and cast I simply solder them

I think you will find it difficult to cast jewelry scale pieces
with a hollow center. On a little larger scale I have
experimentaly cast hollow pieces in bronze about 6" high using
various core methods , wax built around a preformed plaster core
, hollow built sculpture with a plaster core poured in after the
outside is built up., and a plaster core poured into a wax formed
in a mold similar to ceramic slip casting. They all worked but
my intent was to test ways of making larger size sculptures with
less bronze weight. not to make little pieces. Bronze sculptures
are generaly cast with walls about 1/4" to 3/8" thick . I
recomend you look at lost wax casting of sculptures using either
conventional plaster molds in a flask and using ceramic shell
molds. Information can be found on the artmetal site and in a web
search as well as several books. You won’t find things to
enable doing what you desire but will understand the process
better. Jesse

Sandra, Make a hollow wax (slush wax into mold and pour out extra
liquid wax when the “wall thickness” is correct). Cut out or
“drill” holes, 2-4-?? to 1) let investment into the hollow form
and 2) to tie the inner “core” to the outer wall of investment to
maintain the space (what was wax) between the core and the wall
once burned out. Sprue to wax as needed (vent too if needed).
Once dewaxes, burned out and cast, you can get to the investment
inside the hollow form via the holes. Once cleaned out, the
holes are filled, either with a stone, decoration or the cut out,
casted pieces of original wax can be soldered back in place. You
will need to leave some sort of atmospheric opening in the piece
while soldering on it and possibly be able to close this “vent”
as a last operation (much more difficult with silver as so much
heat has to be applied to the entire piece for soldering, there
will be a vacuum inside of hollow form once cooled. Also a
compleatly sealed hollow form can become a
bomb if heated and the inside air pressure gets too high.)

Hope this helps. It is just one way to do this. I am a bronze
caster (sculpture) and I cast most all of the pieces as hollow
pieces. With jewelry, the wall thickness of the casting is going
to be a problem as it is difficult to get much flow distance when
casting as thin as most jewelry items. Most hollow forms are 2
halves (made by stamping and or forming one way or another)
soldered together.

Good luck!! Hope this helps a bit.

John Dach
MidLife Crisis Enterprises
C.T. Designs
Cynthias sculptures are at:
Maiden Metals,
A small bronze foundry, no web site yet!!

Hello Sandra, There is a way to do hollow casting, However, I
don’t recommend going down that path. The amount of work
neccesary to do it Is more than likely not worth the effort on
your side(model making/design and touching up location holes)
and on the casting side where the caster has to Have a mold (of
a model)of the interior of the pieces as well as a corresponding
mold of the exterior with location holes to locate the
interior.Then the caster has to have a waxpot full of water
soluble wax for the interior. A generalized explanation is this
.After having created an interior model and an exterior model. A
rubber mold is made of the 2 items. the items also have to have
corresponding location bars which will also be used to drain the
water soluble wax from the interior. after the molds are made,The
interior mold is injected with watersoluble wax.( this wax
dissolves in water at about 90-100 oF) This wax is then
transfered manually to the exterior mold and a normal , higher
temperature wax that is not water soluble is injected over the
water soluble wax.Now, there must be corresponding holes(fairly
large) for the water soluble wax to drain out from …leaving a
hollow injection wax pattern.The drainage holes Of the interior
must be large enough to allow the Investment to fill the
Interior of the waxpattern and strong enough to survive the
investing process and the casting process. After casting, there
will be investment left inside the hollow casting which now
needs to be removed and that is another story !!! My
recommendation is to Not cast it this way as it will become a
veritable nightmare for all involved. The best way to do this is
to make a 2 part model, cast it in 2 parts and solder the
castings together. Otherwise , have the item electroformed which
is another way to create hollow items. Hope this helps. Daniel
Grandi we do casting, model
making, mold making and finishing for people in the trade…

Sandra, In order to create hollow one piece forms by casting you
need to use water soluble wax. For example, say you wanted to
make a bead, You would carve the water soluble wax into a ball
somewhat smaller than your final product (say 10 mm if you
wanted a 12 mm bead). Then you would coat the water soluble wax
core with regular casting wax. When completed you would soak
the bead in water to eliminate the core. Of course if you
completely coated the surface with wax you would need to drill
holes in the wax to allow the wax a way to contact the water and
drain out. Once the core was eliminated you could then cast the
piece in whatever metal you needed. The interior of the bead,
however needs to be supported. If for example you merely coated
the inner core with "filigree wax, you would doubtfully need any
support. However, if you indeed make cores that have little
connection to the outside (think ping pong ball) you will need
to either create holes that can be filled once the item is cast,
allowing the investment to support the interior, or you should
insert metal pins (preferably of the same metal you are casting
if you want a seamless look) into the core to support the
investment that will fill the space voided by the water soluble
wax. This is the technique used by foundries when casting
hollow sculptures.

Also of importance is the need to have a way to allow the inner
investment to be removed. You can soak the item in investment
removal solution or place the item in a glass beaker and
ultrasonic the item in the investment removal solution to hasten
removal. Make sure you remove all the investment or else when
you solder the item the wet investment turning to steam may
cause the bead to explode.

There are many exciting design options with hollow core casting.
For example make a bead and drill holes in it, for pins use
platinum tubing. Once the item is cst and the investment
removed you have instant diamond bezels in place, no soldering

Larry Seiger

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