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RE: Plaster Moulds for Brass

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  • James Walker
    For about 12 years I lost-wax cast brass, bronze and a little fine silver with a mixture of 1 part fine silica sand, 1 part water and 1 part casting plaster.
    Message 1 of 7 , Aug 2, 2004
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      For about 12 years I lost-wax cast brass, bronze and a little fine silver with a mixture of 1 part fine silica sand, 1 part water and 1 part casting plaster. It worked well for me, holding up well after steaming the wax out, baking and pouring the metal. Of course, you only get one copy, which was OK with me, since I was casting one-of-a-kind art objects.

      -Jim Walker


      James R. Walker, Metalsmith
      Specializing in fine metal repair, restoration, preservation
      Website: <walkermetalsmith.com>
      Publisher, free eNewsletter, "Repairing Metalware:"
      <http://walkermetalsmith.com/repairing_metalware.htm>

      [Non-text portions of this message have been removed]
    • Andrew Werby
      Message: 25 Date: Mon, 2 Aug 2004 17:50:51 -0700 From: Brewer Subject: RE: Plaster Moulds for Brass Take a look at this site. She uses
      Message 2 of 7 , Aug 3, 2004
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        Message: 25
        Date: Mon, 2 Aug 2004 17:50:51 -0700
        From: "Brewer" <brewer@...>
        Subject: RE: Plaster Moulds for Brass

        Take a look at this site. She uses plaster to invest the wax in . Remember
        that you need to fire the plaster and have it at temp before you poor. Any
        moisture in the mold will cause an explosion.
        http://www.stonefire.biz/index.php?page=gallery&gid=13
        Dan in Auburn

        [That site is long on pictures but short on text. The investment material
        used for bronze (or brass) casting contains plaster (gypsum) but isn't just
        plaster. That's like the difference between cement and concrete - the gypsum
        is just the binder; it's the aggregate that makes it work. There are plaster
        molds made for ceramic slipcasting that are straight plaster; they won't
        work for brass. As Dan points out above, all plaster-based molds have to be
        burned out thoroughly before pouring metal into them. This requires
        temperatures of about 1000F - baking in a home oven isn't sufficient, as
        chemically-bound water has to be eliminated as well as free water and all
        traces of wax.]

        Andrew Werby
        www.unitedartworks.com

        -----Original Message-----
        From: uscg_e7 [mailto:uscg_e7@...]
        Sent: Monday, August 02, 2004 9:30 AM
        To: hobbicast@yahoogroups.com
        Subject: [hobbicast] Plaster Moulds for Brass

        Can I use a plaster mould for casting brass?
      • Brewer
        Yes but, I suggest that you find an Art foundry near you that does brass in the lost wax method. They use a ceramic investment system that is sprayed or
        Message 3 of 7 , Aug 3, 2004
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          Yes but, I suggest that you find an Art foundry near you that does brass in
          the lost wax method. They use a ceramic investment system that is sprayed
          or dipped on to the wax positive. The wax is then burned out and the shell
          is fired. When they get enough of the shells to warrant a pour they fire
          the shells again to bring them up to temp The shells are held at temp until
          just before the pour. They are then hung on an iron tree. Then the brass
          is poured into the shells.

          Here is a repost of an earlier message
          I don't use slurry. I don't have the equipment. So I do the next best
          thing.
          First I use plaster and silica flint mixed in equal parts by volume,
          and
          brush a coating on the whole thing to 1/4 inch. We also use a few drops
          of
          Jet Dry, the dishwasher stuff, to the mixture which makes it adhere to
          the
          wax better. This gives the metal a smoother finish without grinding. It
          takes to polishing better. Less grinding means more of the details from
          the
          original wax show in the finished bronze.
          Then I use plaster, sand and what we call "luto" which is old
          investment
          ground back to a powder. It is mixed in equal parts by volume and
          hand
          packed to at least 3/4 of an inch around the wax. Then chicken wire is
          wrapped around the sides and bottom with a final coat of investment to
          hold
          the wire in place. Generally I fill it in and flatten the bottom,
          mainly so
          it is more stable when casting. The luto helps with the expansion
          during
          burnout and casting to prevent major cracking and the chicken wire
          keeps the
          whole thing from coming apart during pouring. I have done some
          experimenting
          with other things to replace the luto. Wet sawdust works. It burns out
          with
          the wax and the investment gets very light weight. It looks a little
          scary,
          being so light weight, but works fine. This method can lead to some
          flashing
          at times especially if care is not taken to make sure than there are no
          air
          pockets while packing it. But very few of my pieces have ended up at
          the
          welder's for repair(less than 10%). Cups and sprews need to be large
          with
          the sprews tapered down to the piece, as metal shrinkage can be a
          problem,
          and the piece needs to be well vented. I did a narrative with pictures
          on my
          web page if you want to go look:
          http://www.stonefire.biz/index.php?page=gallery&gid=13
          The investment process is about half way down the page.
          Burnout is done in an electric kiln adapted for the process, 24 hours
          at
          1100 degrees. It is slightly more complicated than that but if you want
          that
          process too let me know. Then we place the warm investments (about
          300
          degrees) in a tub filled with pumice and sand in case of metal leakage.
          When
          working with students who have never done this before, we occasionally
          have
          a blowout. I have never had one, but I have seen a few and it was
          easier to
          recover the metal from the sand than from the floor.
          If you have any more questions let me know. I am happy to help.
          Amy

          Good luck in your quest Dan in Auburn

          -----Original Message-----
          From: Peter Sibley [mailto:sibleyp@...]
          Sent: Monday, August 02, 2004 7:17 PM
          To: hobbicast@yahoogroups.com
          Subject: Re: [hobbicast] Plaster Moulds for Brass

          Do you think that system could be modified to use a thinner plaster coat ,
          say 10 or 12 mm ( 3/8" or 1/2") then backed up by vibrated sand? It would
          speed the whole process up .
          Peter Sibley

          ----- Original Message -----
          From: "Brewer" <brewer@...>
          To: <hobbicast@yahoogroups.com>
          Sent: Tuesday, August 03, 2004 10:50 AM
          Subject: RE: [hobbicast] Plaster Moulds for Brass


          > Take a look at this site. She uses plaster to invest the wax in .
          Remember
          > that you need to fire the plaster and have it at temp before you poor.
          Any
          > moisture in the mold will cause an explosion.
          > http://www.stonefire.biz/index.php?page=gallery&gid=13
          > Dan in Auburn
          > -----Original Message-----
          > From: uscg_e7 [mailto:uscg_e7@...]
          > Sent: Monday, August 02, 2004 9:30 AM
          > To: hobbicast@yahoogroups.com
          > Subject: [hobbicast] Plaster Moulds for Brass
          >
          > Can I use a plaster mould for casting brass?
          >
          >
          >
          >
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          > This list is for discussion of metal casting
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          > http://groups.yahoo.com/group/sandcrabs
          > Please visit our sponsor: Budget Casting Supply
          > http://budgetcastingsupply.com/
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          This list is for discussion of metal casting
          and does not accept attachments. For off topic discussion and to share
          photos and stuff: join Sandcrabs by sending a blank message to:
          sandcrabs-subscribe@yahoogroups.com
          http://groups.yahoo.com/group/sandcrabs
          Please visit our sponsor: Budget Casting Supply
          http://budgetcastingsupply.com/

          Files area and list services are at:
          http://groups.yahoo.com/group/hobbicast For problems that cannot be
          otherwise solved contact the list owner by email:
          owly@...


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