using microwaves to dewax a plaster silica mould ?!?

rskrishnan · Post by **rskrishnan** » Thu Aug 28, 2003 12:45 am

Hello All,
I have a rather large mould - about 1 cubic foot with a reasonably large wax model in it - the wax model has lots of detail in it. I'm looking for non-traditional ways to de wax the mould. I read a fair bit on microwave oven techniques to dewax a mould. All requiare a rather WET plaster mould. I'm not sure how successful a cured mould is with the microwave approach !!
Has anyone tried the microwave approach to dewax larger moulds (> say 6"x6"x6"). I've had decent success but with small moulds - not large ones. Large moulds are a greater investment of time, energy & "soul" - so hate to screw this up - but am also loath to dewax with steam boiler tech.

Krishnan

charlie · Post by **charlie** » Thu Aug 28, 2003 10:24 am

microwaves work by exciting water molecules, causing them to vibrate fast, which causes heat.

if there's no water in it, microwaves won't heat it up.

watershed · Post by **watershed** » Thu Aug 28, 2003 11:44 pm

sorry to add more rain to the parade. But if you have reinforced the mold with chicken wire, that might cause probs. The whole metal vs microwave thing.

Greg

Lauri Levanto · Post by **Lauri Levanto** » Fri Aug 29, 2003 1:45 am

Most fat molecules behave like water in microwave,
producing heat.
When makin vax models from paraffin, I have
melted the paraffin in microwave.

By wetting the mold you at least prevent the
absorption of vax into mold.

-lauri

jerry flanary · Post by **jerry flanary** » Tue Sep 09, 2003 11:18 pm

Another thing to consider w/ a dry plaster mold is that the melting wax is just going to seep into the plaster (my guess). You need the water in the plaster to resist the molten wax (my opinion).
j.

Lauri Levanto · Post by **Lauri Levanto** » Wed Sep 10, 2003 3:45 am

Jerry Flanary:
... the melting wax is just going to seep into the plaster (my guess). You need
the water in the plaster to resist the molten wax (my opinion).

That is my experience, too. I tried once to remove the residue vax by burning acetone in the mold.
The result was a beautiful cast, filled with
ugly black flakes.

-lauri

jerry flanary · Post by **jerry flanary** » Wed Sep 10, 2003 2:59 pm

Could the Ugly Black Flakes have come from the acetone? Is this what we call acetylene in the states or you reallyjust threw some acetone in there and lit it off?
j.

rskrishnan · Post by **rskrishnan** » Wed Sep 10, 2003 3:28 pm

lauri wrote:Jerry Flanary:
... the melting wax is just going to seep into the plaster (my guess). You need
the water in the plaster to resist the molten wax (my opinion).

That is my experience, too. I tried once to remove the residue vax by burning acetone in the mold.
The result was a beautiful cast, filled with
ugly black flakes.

-lauri

I suspect that the ugly black flakes are from burnt carbon (== soot) that got left behind. It is VERY hard to clean out the soot since it sort of smears itself with the slightest hint of moisture. I've had black spots/flakes in the casting when I had some unburnt wax left behind in an undercut or some "hard to reach" place within the mould.

Krishnan

Lauri Levanto · Post by **Lauri Levanto** » Thu Sep 11, 2003 4:27 am

Sure the flakes were unburnt carbon.

The acetone was a liquid, squirted into the mold and lit.
OUTDOORS !!!
It burns off perfectly clean. I expected it to burn
off the wax residues as well but apparently the very high
heat only made it to seep deeper.

When cooking the glass, that wax gassed out making
bubbles into the glass. Without oxygen the carbon
compounds of wax disintegrated and left the carbon flakes
inside the piece.

-lauri