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42760Re: [hobbicast] Re: Need advice

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  • Dan Brewer
    Apr 11, 2013
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      So here is a link to one supplier.
      http://www.sheffield-pottery.com/U-S-Gypsum-1-CASTING-PLASTER-50-lbs-p/rmcaspla50.htm
      The name of the company is US gypsum not US plaster. Brain fart. The way
      that I use it is to take my wax master with sprus and vent attached and
      coat it in Jet dry. Yes the stuff you use in your dish washer. It breaks
      the surface tension on the wax and allows the plaster to stick. I mix a
      little of the plaster up to the consistency of thin pancake batter and
      paint it on. until I have coated the entire master except the top of the
      pouring cup and the top of the vents. . I let that dry a little miz a
      little more up a little thicker and put on another coat. When still wet I
      sprinkle flint sand on the entire piece. Let that dry for a little. Mix up
      some more plaster about 60/40 plaster sand and coat the piece. Let dry. You
      should have coated the piece about 1.4 to 1/2 inch thick by now. Mix up
      some more plaster 50/50 sand and plaster. sprinkle each coat with sand. The
      next coat should be 30/30/30 plaster /sand / and grog. Grog is previously
      fired plaster that has been broken up in to pieces that will fit through a
      #8 sieve. When you have 3/4 to one inch of plaster wrap the piece in small
      chicken wire. This is to keep the mold from breaking up when you fire it.
      Add another inch of plaster , grog, sand to the outside of the mold. The
      top and bottom of the mold should be able to support the mold with out
      tipping over. The top because when you fire it the top will be down so all
      of the wax will leave the mold and the bottom so you can fill the now
      vacated mold with metal. Let dry .for several days in a warm spot. I place
      mine on a blotter board. My blotter board is a 2x2 piece of drywall.
      Place in your kiln and heat at the rate of 100 deg f per hour until the
      melting temp of the wax has been reached. My kiln has a stainless steel
      sink in the bottom that is plumbed out the bottom to get some of the wax
      out of the kiln. I am able to recover some of it but not much. after the
      wax is out around 200 to 275 deg you can ramp up a little faster Fire at
      2000deg f for 4 to 20 hours depending on size of the piece. Let cool to
      around 400 deg and pour.. Cover the pouring cup and vents with perlite or
      vermiculite and let cool. When the outside of the mold is just hot enough
      to touch sweep off the perlite/ vermiculite and you can remove the
      plaster. Remember that it will be hot. I use a hammer and a water hose to
      remove most of the plaster . Plaster will clog your drain . More clean up
      can be done with a stiff brush or sand blasting.
      For more information look up lost wax casting , ceramic shell casting.

      Dan in Auburn

      Other places to find casting plaster are pottery suppl houses. jewelery
      supply houses. And there are lots of formulas of the casting plaster. This
      is just the one that I have been using.


      On Thu, Apr 11, 2013 at 11:56 AM, Inventor <welfab@...> wrote:

      > **
      >
      >
      > Hey Dan,
      > About a half a dozen links wouldn't hurt....
      > A few to read up about it.
      > A few more as to where to buy it for "20 BUCKS"
      >
      > All I've found was clay and that 'started' at $85/50#.
      >
      > Grandpa Bill
      >
      >
      > --- In hobbicast@yahoogroups.com, Dan Brewer <danqualman@...> wrote:
      > >
      > > On of the problems with using POP is that it is hygroscopic meaning that
      > > the material will never release all of the water trapped in its
      > structure.
      > > It actually will draw water out of the atmosphere . I would use a
      > material
      > > that when fired will vitrify and change to a substance that now will
      > reject
      > > water. American plaster makes casting plaster. 50 lbs goes for about
      > > 20USD . There are several others. Plaster of Paris is best left to the
      > > art casting for statues.
      > >
      > > Dan in Auburn
      >
      >
      >


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