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Re: [casting] Re: got multi-piece flexible mold examples?

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  • Mike Brose
    ... Very interesting piece. Don t thank me yet! Let s see if we can find some solutions for you. First of all how tall is the sculpt? Are you going to
    Message 1 of 6 , Aug 30, 2001
      On Thu, 30 Aug 2001 21:04:03 -0000 d3s1gnr@... writes:
      > Hi Mike,
      >
      > You have an impressive range of work! I had seen your other sites,
      > but not the earthly creations pieces.
      >
      > The sculpture I'm creating is probably most similar to the leopard
      > frog or tree frog in the sense of undercuts. I put some pictures of
      > it up on my site for reference-
      > www.lucidart.com/gallery/sculpture_in_progress.htm
      >
      > The notion I have now is that a three-piece mold could work (one
      > piece in back, 2 in front, the break being at the cupped hands).
      > This
      > however still doesn't get me past the difficulty of a seam on the
      > top
      > face.
      >
      > Any ideas you have would be great!
      >
      > thankyou thankyou,
      >
      > Dawn


      Very interesting piece.

      Don't thank me yet! <G> Let's see if we can find some solutions for you.
      First of all how tall is the sculpt? Are you going to add any more
      elements, other than details, to the piece? Is that water base or oil
      base clay? What type of casting material will you be pouring into the
      finished mold?

      Going from single piece molds to this project could be a good size jump!
      <G>

      I see some possible promblems for air entrapment, if you are going to
      make solid castings. This would be where the back of the hands are on the
      front of the sculpt. Take the photo of the side view of the sculpt, turn
      it upside down. This will give you a view of how the mold will sit when
      completed and where the casting material will be poured in. Imagine the
      inside of the empty, completed latex mold. As you start pouring casting
      material in (which will first start filling where the top head is on the
      sculpt), it will be fine until it rises to where the hands are (from what
      I can see at first glance). It will fill in part of the hand area, but at
      a certain point will trap air (near where the knuckles are). The air has
      no where to go. You will have a void or huge air pockets in that area of
      the finished casting.

      Of course if you are not planning on doing solid castings, that might not
      be a problem.

      If you look at all the different sculpts on the Earthly Creations web
      site, if you envision them upside down, you will see that all of them
      have been sculpted so as to not run into the above problem. In sculpting
      and making molds for statuary and or cast concrete items, it is fairly
      common to try to avoid this situation by designing the sculpt without
      such areas, as it makes for simpler molds and quicker production.

      I think you could possibly get by with a one piece latex mold with a
      seam in it, along one side, close to the back. You mainly need a seam so
      that the latex mold can be removed from the model (and later castings)
      with out too much trouble. You can use the plastic shim and bubble stock
      (as on my site, and stick them into the clay. Ideally it would be best if
      the seam was at a place where the mother mold was going to part at any
      way. That way the mother mold will help keep the seam together while you
      are casting. I'll send you a separate photo off list so you can see what
      I mean.

      You have a fair amount of undercuts on the piece, some of which would be
      best filled in with thickened latex (your supplier will probably have
      something that you can use to do that with), to eliminate the undercuts
      (like the open palm of the hands, the back of the hands, the inside of
      the ears and other such places). If it were a small enough piece, I
      personally would make a rubber mother mold that goes around the piece,
      which would eliminate all the undercuts pretty much, and you can then get
      by with a simpler rigid mother mold that goes around the rubber mother
      mold (which in turn supports that latex mold). But, depending on the size
      of the piece, a 2 or 3 piece mother mold could be best.

      I know some mold makers that fill in the undercuts with urethane rubber
      (thickened with Cab-O-Sil), and then cover over these filled in areas
      with more latex. That way, these little sections of urethane become part
      of the mold. Some mold makers take some fabric and cover over the
      undercut area, an then cover the fabric with latex, several layers. This
      makes an air filled cushion within the undercut. This works best if it's
      not too big an area, or not an area that will have a lot of pressure from
      the casting material. So again, it can depend on whether you are doing
      solid casting or not.

      Mike Brose

      http://puppetsnprops.homestead.com/ventbook.html (New figure making
      book!)
      http://puppetsnprops.homestead.com/home.html (sculpt, mold, mothermold,
      cast, etc)
      http://www.jugglingstore.com/products/zsiliconeballs.html (silicone
      juggling balls)
    • d3s1gnr@yahoo.com
      Wow, this is alot of information... Looks like I will indeed be making a leap, since I clearly wasn t thinking in terms of production during sculpting!
      Message 2 of 6 , Sep 2, 2001
        Wow, this is alot of information... Looks like I will indeed be
        making a leap, since I clearly wasn't thinking in terms of production
        during sculpting! <g>

        Let's see if I can give you a little more information...

        The sculp is about 17" high and 8" wide/deep in it's largest (bottom
        area) parts. I'm pretty much done with it at this point, only tiny
        refinements to texture are happening.

        The clay used was WED clay, a water-based type. I've been unable to
        find out whether it is sulphuric or not at this point. I tested it
        with latex and no mold release (other than dish soap)was necessary.

        The type of casting I'd envisioned doing was indeed solid- some kind
        of hardened plaster substance suitable for outdoor display
        (FMG/Forton combination, for example). Because of this, I'm guessing
        that the fabric/air cushion trick wouldn't work

        I am currently building a different 2-piece latex mold using
        thickened latex to get rid of undercuts, so using thickened rubber to
        simplify the mother mold should be a doable, if time-intensive
        process.

        A couple of questions about possible strategies:

        Would adding a seperate "fill hole" or sprue on the hands help
        matters by giving the air someplace to go?

        Alternatively, could the piece be laid on it's back (where the feet
        are) using appropriate supports, or would that cause more issues than
        it fixed?

        Thanks again for your input. I'll be buying that book soon!

        Dawn

        --- In casting@y..., Mike Brose <propworks@j...> wrote:
        >
        >
        > On Thu, 30 Aug 2001 21:04:03 -0000 d3s1gnr@y... writes:
        > > Hi Mike,
        > >
        > > You have an impressive range of work! I had seen your other
        sites,
        > > but not the earthly creations pieces.
        > >
        > > The sculpture I'm creating is probably most similar to the
        leopard
        > > frog or tree frog in the sense of undercuts. I put some pictures
        of
        > > it up on my site for reference-
        > > www.lucidart.com/gallery/sculpture_in_progress.htm
        > >
        > > The notion I have now is that a three-piece mold could work (one
        > > piece in back, 2 in front, the break being at the cupped hands).
        > > This
        > > however still doesn't get me past the difficulty of a seam on the
        > > top
        > > face.
        > >
        > > Any ideas you have would be great!
        > >
        > > thankyou thankyou,
        > >
        > > Dawn
        >
        >
        > Very interesting piece.
        >
        > Don't thank me yet! <G> Let's see if we can find some solutions
        for you.
        > First of all how tall is the sculpt? Are you going to add any more
        > elements, other than details, to the piece? Is that water base or
        oil
        > base clay? What type of casting material will you be pouring into
        the
        > finished mold?
        >
        > Going from single piece molds to this project could be a good size
        jump!
        > <G>
        >
        > I see some possible promblems for air entrapment, if you are going
        to
        > make solid castings. This would be where the back of the hands are
        on the
        > front of the sculpt. Take the photo of the side view of the sculpt,
        turn
        > it upside down. This will give you a view of how the mold will sit
        when
        > completed and where the casting material will be poured in. Imagine
        the
        > inside of the empty, completed latex mold. As you start pouring
        casting
        > material in (which will first start filling where the top head is
        on the
        > sculpt), it will be fine until it rises to where the hands are
        (from what
        > I can see at first glance). It will fill in part of the hand area,
        but at
        > a certain point will trap air (near where the knuckles are). The
        air has
        > no where to go. You will have a void or huge air pockets in that
        area of
        > the finished casting.
        >
        > Of course if you are not planning on doing solid castings, that
        might not
        > be a problem.
        >
        > If you look at all the different sculpts on the Earthly Creations
        web
        > site, if you envision them upside down, you will see that all of
        them
        > have been sculpted so as to not run into the above problem. In
        sculpting
        > and making molds for statuary and or cast concrete items, it is
        fairly
        > common to try to avoid this situation by designing the sculpt
        without
        > such areas, as it makes for simpler molds and quicker production.
        >
        > I think you could possibly get by with a one piece latex mold with
        a
        > seam in it, along one side, close to the back. You mainly need a
        seam so
        > that the latex mold can be removed from the model (and later
        castings)
        > with out too much trouble. You can use the plastic shim and bubble
        stock
        > (as on my site, and stick them into the clay. Ideally it would be
        best if
        > the seam was at a place where the mother mold was going to part at
        any
        > way. That way the mother mold will help keep the seam together
        while you
        > are casting. I'll send you a separate photo off list so you can see
        what
        > I mean.
        >
        > You have a fair amount of undercuts on the piece, some of which
        would be
        > best filled in with thickened latex (your supplier will probably
        have
        > something that you can use to do that with), to eliminate the
        undercuts
        > (like the open palm of the hands, the back of the hands, the inside
        of
        > the ears and other such places). If it were a small enough piece, I
        > personally would make a rubber mother mold that goes around the
        piece,
        > which would eliminate all the undercuts pretty much, and you can
        then get
        > by with a simpler rigid mother mold that goes around the rubber
        mother
        > mold (which in turn supports that latex mold). But, depending on
        the size
        > of the piece, a 2 or 3 piece mother mold could be best.
        >
        > I know some mold makers that fill in the undercuts with urethane
        rubber
        > (thickened with Cab-O-Sil), and then cover over these filled in
        areas
        > with more latex. That way, these little sections of urethane become
        part
        > of the mold. Some mold makers take some fabric and cover over the
        > undercut area, an then cover the fabric with latex, several layers.
        This
        > makes an air filled cushion within the undercut. This works best if
        it's
        > not too big an area, or not an area that will have a lot of
        pressure from
        > the casting material. So again, it can depend on whether you are
        doing
        > solid casting or not.
        >
        > Mike Brose
        >
        > http://puppetsnprops.homestead.com/ventbook.html (New figure making
        > book!)
        > http://puppetsnprops.homestead.com/home.html (sculpt, mold,
        mothermold,
        > cast, etc)
        > http://www.jugglingstore.com/products/zsiliconeballs.html (silicone
        > juggling balls)
      • Mike Brose
        Dawn........ my comments are interspersed below. ... Generally you do not need mold release with latex (the only thing you really need is to seal a porous
        Message 3 of 6 , Sep 2, 2001
          Dawn........ my comments are interspersed below.

          On Sun, 02 Sep 2001 21:15:53 -0000 d3s1gnr@... writes:
          >
          > The clay used was WED clay, a water-based type. I've been unable to
          > find out whether it is sulphuric or not at this point. I tested it
          > with latex and no mold release (other than dish soap)was necessary.

          Generally you do not need mold release with latex (the only thing you
          really need is to seal a porous model). In fact mold release can work
          against you with latex and in some cases cause delamination of the layers
          of latex depending on what type of mold release is used. I really
          haven't made any latex molds from a water based clay, but I do know that
          if there is too much moisture in the model, that can sometimes cause
          problems. So just be sure that it won't be an issue before going to all
          the trouble of making the mold. I know with a plaster or Hydrostone
          model, if it freshly made and hasn't dried properly, it can ruin a latex
          mold. Years back, I got in a hurry and applied latex over a Hydrostone
          model that wasn't completely dry. I went through the whole process
          including mother mold, only to find out the inner layers of latex did not
          cure properly (because of the moisture in the model) and the mold was
          ruined when I demolded the piece. A lesson I'll never forget! <G>

          > The type of casting I'd envisioned doing was indeed solid- some kind
          > of hardened plaster substance suitable for outdoor display
          > (FMG/Forton combination, for example). Because of this, I'm guessing
          > that the fabric/air cushion trick wouldn't work

          It could work, but when in doubt, always go for full support with the
          mother mold.

          > I am currently building a different 2-piece latex mold using
          > thickened latex to get rid of undercuts, so using thickened rubber
          > to simplify the mother mold should be a doable, if time-intensive
          > process.

          Mostly need to try to prevent mother mold 'lock' on the latex mold,
          otherwise the only reason to get rid of more undercuts would be to reduce
          the number of pieces for the mother mold.

          > A couple of questions about possible strategies:
          > Would adding a separate "fill hole" or sprue on the hands help
          > matters by giving the air someplace to go?

          If you are going to cast Forton MG, you could avoid problems by casting
          the problem area first (lay the mold face down and fill this area or do a
          hand lay up of the FMG). After the material starts to set, pour the mold
          full for a solid casting. Thus a combination of 2 techniques. You would
          also avoid having sprue marks to clean up on the finished castings. It
          might be easier perhaps to do the above technique with a two piece latex
          mold that could be opened for applying the Forton MG to the problem area.



          > Alternatively, could the piece be laid on it's back (where the feet
          > are) using appropriate supports, or would that cause more issues
          > than
          > it fixed?

          I think it would probably create more problems. The bottom of your piece
          naturally forms a good place for an opening in the mold. No need to
          complicate it.


          >
          > Thanks again for your input. I'll be buying that book soon!
          >
          > Dawn

          You're welcome!

          Mike Brose
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