Pewter and Bronze Casting for the Home Craftsman

   High-quality metalcasting can be done in the home shop using mostly
locally-available materials and equipment and at very reasonable cost.

   A simple process to cast pewter with a minimum of expense is described
first. The pewter is melted in a frying pan or iron pot on a propane camp
stove.  It is then cast in silicone-rubber molds, which can be reused
indefinitely.

   Bronze is melted in a foundry assembled using loose insulating firebricks.
The heat source is a common propane torch used for melting driveway ice or
burning weeds.  The bronze can be melted in ironware, but it will stay coated
with bronze.  A graphite crucible is best.

   Wax intermediates can be produced in the same silicone rubber molds used
for casting pewter.  The wax is then used to make molds for casting bronze.
This allows many of the same art pieces to be cast in bronze repeatedly.

   Wax has long been the conventional art material around which a mold was
formed for casting bronze.  The wax art master was covered with special
high-temperature plaster ("investment") which then hardened and dried. Next
the wax was "burned out" (vaporized, no flame), forming a hollow mold. Molten
bronze, brass, silver or gold was then poured into the investment mold.

   If flat artwork like medallions, signs, plaques and handprints are to be
cast, the silicone rubber mold is not necessary.  Pewter can be cast directly
in reinforced plaster molds that have been dusted with talc. Bronze can be
cast directly in reinforced investment molds that have been dusted with
graphite.

   The same torch used for melting bronze can also melt aluminum in the iron
cookware used for melting pewter.
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                       DIRE WARNINGS TO HEED!
PEWTER CASTING:
1. Do not cast copyrighted art pieces to sell.  However, they can often be
   useful when perfecting your casting technique.

2. Always use a face shield when hammering anything.

3. Hobby-knife blades are extremely sharp and will cut you just as
   effortlessly as they cut silicone rubber.

4. The propane camp stove flame is very hot. And any pan or pot on the flame
   will also be very hot. Use high-temperature barbecue mitts or a removeable
   extension handle whenever handling the pan or pot.  Take the extension
   handle off when not handling the pan or pot so that it will remain cool.

5. Pewter melts at 465 F and it is very fluid when it melts.  It can spill
   and splash around your work area when molten.  Splashing it on bare skin
   is very uncomfortable.  However, MPK pewter contains no toxic metals.

6. The final cast pewter piece will stay hot for a long time in the silicone
   rubber mold.  Wait a couple hours before removing it.

7. Never pour clay, plaster or investment down a home drain.  Use a hose
   outdoors to rinse off all tools and mixing bowls.

BRONZE CASTING:
8. Investment contains fine silica, and a cheap paper paint mask will not
   keep all of it out of your lungs.  Silica dust will damage your lungs.

FOUNDRY:
9. The flame from the propane ice-melter torch is 2150 F.  The white-hot
    crucible full of molten bronze will be this hot as well.  A welder's
    jacket or heavy denim jacket, heavy denim pants, heavy gloves or barbecue
    mitts, heavy boots and a full face shield are reassuring to have between
    you and that molten metal.  Polyester will melt if it gets very hot when
    near the foundry, and then it will stick to your skin. Your hair will be
    singed, shrivel up and stink if you look down into the lid vent while the
    torch is fully on.

10. Turn the torch off and use the extension handle whenever:
     a. probing or stirring the melt with a steel rod
     b. adding flux using a long tea spoon in an extension handle
     c. skimming the surface of the melt with an expendable long tea spoon

11. A dropped crucible full of molten bronze will splatter the molten metal
    far and wide.  Dry, flammable fuels such as wooden parts of buildings
    will be charred and possibly ignited.  The liquid metal will go thru
    polyester clothing without even slowing down.  Concrete will be stained
    a unique, dark-green filigree pattern that is fascinating to behold.
    Use pool acid to return some semblance of whiteness to the concrete.
    Prepare believable lies to tell everyone in advance of this memorable
    event. But the good news is that a Salamander brand graphite crucible
    (probably) will not break!

12. If you or anyone trips on the propane hose leading to the torch and the
    torch tips over while it's fully on, it can start dry structural wood
    smoldering instantly.  Have a fire extinguisher or a hose with a trigger
    nozzle (turned on at the faucet!) ready. If the torch flame should happen
    to fall directly on the propane tank, your whole day could be ruined.
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                           PEWTER CASTING
                   The Mother-Mold-First Technique

  This metal-casting technique requires no high-temperature foundry and uses
no cope-and-drag sand-casting mold, which limits the intricacy of castings.
It uses a minimum of costly RTV (room-temperature vulcanizing) silicone
rubber and does not use any vacuum equipment.

  The sunbathing girl and the Buddha were cast in pewter. The doll's face
  was cast in bronze in an open mold, the way a plaque or handprint is cast.

1.  Make your art original using ordinary (wet) or wax clay, not plasteline.
    Form  a hole in the piece approximately 1/4" to 3/8" wide and about 2"
    deep for a support.  There must be a support rod secured into the art
    piece.  This support will pass through where the pouring opening will be
    located.  Wet clay must be fired before making the mold around it.
    -or-
    If an existing piece is to be reproduced in pewter, use double-stick
    foam mounting tape to attach a support to it. If the piece is hollow with
    an opening on the bottom, you can use plaster inside the opening to
    secure a support rod into it.

    -or-
    If your art original or an existing master is a flat piece, such as a
    plaque, medallion or sign, go to the PLAQUE chapter now.

2.  Wrap the master with bubble-wrap, bubbles in, and secure the wrap with
    tape.  The thickness should be about 3/8" to 1/2" for a 6" to 8" piece.
    The thickness of the wrapping will be the thickness of the final RTV
    silicone rubber mold.  This mold must not be too thin and floppy, but
    also must not be wasteful of the costly RTV silicone rubber. One package
    (1.1 lb.) of clear Akron RTV rubber makes 2 cups in volume.

3.  Make a minimum-sized plaster tub using a cardboard box lined with
    aluminum foil. The box should clear the wrapped master by about 3/4"
    all around. Pour water in the mixing bowl and add plaster to the water,
    NEVER water to the plaster. In the case of the sunbather figurine, about
    two cups of water were used.  Let it sit a minute and then whisk it to
    pancake-batter consistency.  Add more plaster or water as needed.  The
    plaster should be stiff enough to maintain a wavy surface, but not runny,
    and likewise not so stiff that it holds its shape firmly.

    Spoon the bottom plaster layer down. We put bronze screening and/or metal
    mesh in the plaster so it won't spread apart if it should crack. Bed the
    wrapped master in the plaster to a minimum of 3/4" up from the bottom so
    that the master is half-submerged. It may be necessary to put a weight on
    the piece if it is light and would otherwise float.  Leave the pouring
    hole open.  Leave the plaster surface uneven and wavy, or make furrows
    in it with your finger.  Let the plaster set up overnight.

4.  Mix up more plaster the next day. Spoon out plaster for the top layer so
    as to cover the wrapped master to a minimum depth of 3/4". Add screening
    and/or metal mesh for strength.  Let this top layer set up overnight.

5.  Mark the support rod's exact depth, right-left position, front-back
    position, right-left angle, front-back angle and twist angle directly
    on the plaster.  This step is extremely important!

6.  Split open the plaster halves with a hammer and screwdriver or hammer and
    hammer-handle wedges.  Tap at several places a little at a time until
    they pop apart.  Remove the master and remove the bubble wrap.

7.  If the master is fired clay, brush a very thin coat of Vaseline or baby
    oil on it for a mold release.  Ceramic, metal, plastic and similar non-
    porous materials need no mold release.  Reassemble the master inside the
    plaster halves. Secure the plaster halves together with long springs
    and/or several folder-size rubber bands.

    Support the master inside the plaster halves using a stand.  Adjust the
    support rod to the exact depth, position and angles marked on the plaster
    in step 5. If the master is not exactly centered, the mold will be too
    thin in some places and too thick in others.  If the master touches the
    plaster anywhere, there will be a hole in the mold where it touched!

8.  Open the jar of Akron RTV silicone rubber. Put duct tape around the jar
    to raise the jar wall up an inch.  Pour in all of the catalyst. Mix very
    slowly with a table knife, scraping the rubber out from the sides of the
    jar and in toward the center.  It is best to hold the knife still and
    slowly rotate the jar.  Occasionally move the knife to the center, lift
    it up and then lower it down again. This will get the contents on the
    center and bottom into the mix.

    Few bubbles will stick to the master. But if they do, they will become
    small balls of metal that will be easily removed later. But any closed
    bubbles that form near the master will expand from the heat of the metal
    and become dimples in the figurine.  The dimples must be filled using a
    soldering iron and pieces of pewter after casting.
    Or you can use the point of a hobby knife to pierce down to the bubble
    in the silicone rubber mold so that air will not be trapped inside the
    bubble when casting.

    Start the RTV silicone rubber into the mold by tipping the jar, as if
    pouring very cold syrup. Form the duct tape into a spout.  Then tip the
    jar back to slow the flow so that it does not pour too fast, overflow and
    dribble down outside the plaster. But if it does, just spoon it back into
    the opening.  The flow is slow enough so that there is time for such
    mishaps to be corrected. Near the end, you will need to scoop out the
    last of the mold rubber with the knife.  Let the mold cure for 24 hours.

9.  Remove the long spring or rubber bands, pop open the plaster halves and
    remove the mold.  The surface will be frosted.  To make it clear when
    cutting the mold apart, use a new blade in a hobby knife to cut away
    the frosted surface along the parting line. This will leave a clear band.

      Cut out the master using the hobby knife.  Cut along the outline of the
    piece so that it will form mating mold halves. As you cut, use your other
    hand to spread the RTV mold apart behind the cut for easier progress.

      Stretch and then cut any front-to-back sections that will become
    openings in the casting. In the case of the sunbather figurine, these
    are the two arm openings.  The only opening in the buddha is between the
    thumbs and fingers.  The girl holding the cat had no openings.

10. Sprinkle talc inside the RTV mold and spread it around with a brush that
    is used for talc only.  Clap the halves together to remove excess talc.

   NOTE: Step 11 can be done two ways. Read both options and select one.
11.
 A. Bed one RTV mold half securely into the best mother mold plaster half.
    Mate the other RTV mold half over it.  Mix up fresh plaster.  Spoon new
    plaster around the RTV mold seam so that the halves remain properly mated.
    Look inside the opening to check that they are still mated. Spoon more
    plaster over the seam plaster and then up and over the top of the RTV
    mold so that it is fully buried.  Again look in the opening and make
    certain the mold seam has not shifted.  Put screen and/or metal mesh in
    the plaster for strength.  Have a minimum depth of 3/4" at the top and
    sides. Let this set up overnight.

    Go to Step 12.

 B. If the mold has an obvious base, the RTV mold can be held together with
    rubber bands. Be sure the seam stayed mated properly everywhere after
    putting on the rubber bands.  Seat this on a piece of aluminum foil so
    that it is sitting on the pouring opening.  Spoon plaster all over the
    mold so that it is about 3/4" thick.  Wrap chain around the plaster, but
    do not push the chain into to plaster or else it will be difficult to
    remove later.  Let the mold dry overnight.  Place the dry mold in the
    freezer.

    Go to Step 13.

12. Put a long metal spring around the plaster mother mold before pouring
    pewter into the RTV.  This is because the hot metal can make the halves
    pop open. Have a drip pan under the mold just in case that does happen.
    Put the mold and drip pan in the freezer overnight.

13. When ready to cast the piece, melt the pewter in the iron pan or pot
    on the camp stove. Stir and check for unmelted lumps with a long tea
    spoon. Skim off the surface skin with the spoon after it has all melted.
    Put on barbecue mitts. Get the mold from the freezer and place it near
    the camp stove.

14. Turn off the gas and skim the surface one last time. If you use a pan for
    melting the pewter, when you pick it up, hold it firmly so that it does
    not slosh. (The pot will not slosh as much as the pan.)  Pour the pewter
    into the mold, up to the bottom of the pouring opening.  Put the pan or
    pot back on the stove.

    Tap the mold to release bubbles and tilt it around in all directions to
    fill every crevice of the mold. Now fill up the rest of the pouring
    opening with pewter. Pour excess pewter into the cornbread mold cavities.

    Prop the mold so that the metal puddle is level if it will be the base
    or stand of the piece.

15. Wipe out any pewter sticking inside the pan or pot with a paper towel
    while the metal is still hot and fluid.  The paper may become charred in
    the process.

16. After the casting cools, remove the long spring and wedge apart the
    plaster halves with the screwdriver or wedges. If the mold was wrapped
    with chain, pull the chain off and use a hammer to crack the plaster off.
    Remove the RTV mold and take out the casting.

    Check the casting for fidelity with the master. Some types of pewter may
    not flow into the very smallest details of some molds by gravity alone.
    Hallmark MPK pewter has a nice surface finish and is so strong that it
    rings like a bell, but it won't flow into some very small mold features.
    But other pewters didn't, either. If fine detail is desired, pressure or
    centrifugal casting methods must be used.

    Cut off the pouring opening with a hacksaw.  File or grind off any seam
    flashing and wire-brush and/or sand-blast the final finish to suit.

   Here is another pewter casting of the sunbather and one of a girl holding a
   cat. The master for the girl and cat was the cap from a bottle of perfume.

Oops! If the figure is not what you wanted, saw it up, melt it down, pour it
      into the cornbread mold and try again.  Some molds may require more
      plaster coverage if any unplastered seams want to spread apart when the
      hot metal is poured in. Also, try holding the RTV mold halves together
      with rubber bands before covering with plaster. You can also stick pins
      in to hold any stubborn seams together.  But tape will not stick to it.
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     EQUIPMENT:                        SUPPLIES:
     -------------------               -----------------------------
     mixing bowl                       Akron RTV silicone rubber kit(s)
     whisk                             duct tape
     large spoon                       plaster of Paris
     long tea spoon                    pewter ingots
     long spring(s)                    propane cylinder(s)
     propane camp stove                aluminum foil
     iron pan or pot                   talcum powder (not cornstarch)
     iron cornbread mold               misc. cardboard boxes
     support stand                     #16 rubber bands
     soft brush for talc (only)        folder rubber bands
     drip pan                          paper towels
     hammer                            toilet-flapper chain (see photo 34)
     screwdriver and/or hammer wedges  bronze screening and metal mesh
     barbecue mitts                    straight pins
     hacksaw
     file
     wire brush
     soldering iron (80 watt)
--------------------------------------------------------------------------
 SPECIAL SUPPLIES:
    Hallmark Metals -  MPK no-lead silver pewter.         1-888-467-8000
    Akron RTV Silicone - www.zeroproducts.com/index.html  1-800-382-3271
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                    MAKING A PLAQUE OF PEWTER OR BRONZE:

         If the art piece is a flat plaque, medallion, sign or handprint,
       many of the above steps are not necessary.  And if it is to be a
       one-time-only casting, no costly RTV rubber mold is required.

    1.   Make a minimal-sized mold bed from a box lined with aluminum foil.
       It should clear the piece by about 1/2". Put bronze screening and/or
       metal mesh in the bottom. If the piece is to be pewter, use plaster.
       If it will be bronze, use investment (high-temperature mold, which is
       plaster plus fine sand).

    2.   Paint the master with a thin coat of Vaseline if it is fired clay.
       Spread, brush or flick freshly-mixed mold material into all crevices
       of the piece that could trap a bubble.

    3.   Pour about an inch or two of mold material into the box.

  For a HANDPRINT (or footprint), go to that section below.

    4.   Push the master down into the mold material in the box. It may be
       necessary to weigh the piece down if it is light and would otherwise
       float.

    5.   After the mold hardens, remove it from the box and peel the foil off
       of the bottom.  Remove the master.  Fill any large bubble holes with
       fresh mold material.  Small bubble holes will be cast as bumps and can
       be ground or chipped off later.  Wait a day for the mold to dry.

    6.   Heat the mold in an oven at 500 F until it stops steaming. If you
       will not be casting right away, put the mold in a plastic bag to keep
       it dry.

  PEWTER:
    7.   Sprinkle talc into the plaster mold, spread it around with a brush
       used just for talc and blow or brush away any excess powder.  The mold
       can be held upside down for this.
         Melt pewter in the pan or pot. Be sure that the mold is level. Pour
       the pewter in.  It will be necessary to move the pan around the mold
       as you pour if the piece has open spaces in between the areas that
       will be metal.

    8.   If more than one pewter casting is desired, make a foil-lined box
       for the master which is about 1/2" larger all around.  Mix up RTV as
       described in the PEWTER CASTING section. Pour it over the master to a
       depth of about 1/2" above the bottom of the art piece. (A fired-clay
       master must first be coated with Vaseline or oil.)  Work any bubbles
       out of the RTV rubber that appear to be stuck on the master using a
       pin. But most bubbles should just float to the surface on their own,
       which will be the bottom of the mold.

  BRONZE:
    9.   Bronze can be cast directly into a flat investment mold.  It MUST
       have bronze-screening reinforcement.  It will require several days to
       dry completely. In addition, bake it at 500 F until it stops steaming.
       Dust the mold liberally with graphite and spread it around with a brush
       used only for graphite.  Place the mold on some bricks. Molten bronze
       will (Usually) crack the mold, but the flashing (metal that went into
       the cracks) will be very thin and easy to remove.

  HANDPRINT or footprint:
    10.  Mix mold material that is semi-stiff.  Test that the mold material
       will hold an impression by using your finger in a corner.  If it will,
       press the hand or foot down into the plaster.

    11.  If it is a young child's or a baby's hand, take it out slowly and
       cleanly, heel of the hand or foot first, fingers or toes last. If it
       is an adult's, leave it in until the mold begins to set (gets warm.)

         Cast the piece in pewter as described in that section or in bronze
       as described in that section.

         The original impression for this young girl's hand was done in
       plaster. The French wax transfer positive was then used to make an
       impression in investment, but not melted.  Bronze screening, visible
       at the corners, was used for reinforcement.  This particular mold was
       heated to 1,000 F and then allowed to cool to room temperature. It was
       dusted liberally with graphite before the pour. The bronze casting has
       been wire-brushed.

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                MAKING A LOOSE-FIREBRICK BRONZE FOUNDRY
               AND A LOOSE-CHIMNEY-BRICK WAX-BURNOUT OVEN

    A firebrick foundry is the easiest way to melt bronze in the shortest
time for pouring small bronze castings. The one described here uses a common
blowtorch made to melt ice off driveways or to burn weeds.  The disassembled
foundry stores in a small space and assembles quickly and easily when needed.

    The torch produces 500,000 BTUs. The valve adjusts the idle flame.  The
trigger opens the gas flow valve for full fire.  But the valve can also be
opened to produce full fire.  Our pyrometer indicates that the highest
temperature was 2150 F at a point 11"-13" from the end of the burner.  So it
must that far from the end of the burner to the bottom and side of the
crucible. This is very important!  The fire enters from the side of the
foundry in such a way that it hits the side of the crucible at the place
between the bottom of the crucible and the kiln shelf shard that it sits on.
The flame then swirls around the crucible and exits out through the central
vent in the lid.  Do not aim the flame directly onto the crucible.

    The torch makes a loud, jet-engine-like roar when operating properly.
Condensation on the propane tank will show the propane level in the tank.
That level needs to be on the vertical part of the side, above the curved,
bottom part.  Propane in the bottom part does not have enough surface area
to vaporize fast enough for the proper, very hot, very loud flame. The torch
orifice is .059 inches, so it uses a large flow of propane.

   After the torch is on for a long time, the propane gets cold and will not
evaporate fast enough. You may even see frost on the tank. When that happens,
you need to pour a few gallons of boiling hot water on the tank.  You will
then hear the sound increase to what it should be.

   It's best to have two tanks and swap them when necessary, rather than let
the foundry, crucible and molten metal cool down and have to be reheated all
over again after a single tank is refilled.

   The crucible and molten bronze are white-hot when ready to pour, like
standing too close to a roaring fireplace, so be dressed for it.  And fluxed
bronze will coat a cast iron crucible (which is how cast iron is "welded"),
so it is best to get a true graphite crucible.

   We made a 14-ga. steel box pan for the kiln shelf base and bottom layer of
firebricks for ease of handling. But that is not necessary if the foundry can
be left set up somewhere.

   When leaks open up as the furnace is fired up and the bricks expand, just
push them shut with the crucible tongs.  Later, we added a 14-ga. steel outer
shell to the sides and back wall, bent to shape and held on by its own spring
force. But this is also not essential.

   The lowest four and a half firebricks lie flat on top of a kiln shelf.
Seven full bricks and one cut to 6" are stacked on edge for the walls and
flame opening.  The flame opening is 3" wide. Two and two halves of firebricks
form the lid, which has a 4" long opening.  The lid bricks are clamped in a
steel frame which has coathanger-wire lifting handles. Even these wire handles
get very hot, so wear high-temperature barbecue mitts when removing the lid.
Rest the lid on kiln shelf shards when it is hot, never directly on concrete.
The moisture in concrete will make it pop and blister.

   The kiln shelf foundry base can rest on concrete blocks or on a steel
stand. The crucible rests on a kiln shelf shard inside the foundry.  A Lodge
27C2 cornbread mold is great for casting ingots. (Warning: Some cornbread
molds have a mystery coating that does not work well.)  Armil makes great
insulating firebricks.  Salamander makes the best crucibles.

PARTS FOR THE LOOSE-FIREBRICK, PROPANE-FIRED BRONZE FOUNDRY:
      Harbor Freight #36346 or Northern Tool #171717 propane torch
      20-lb. propane tank(s), no regulator required
      (16) firebricks (two sawed in half, one sawed to 6")
      (2) concrete blocks or a steel table
      lid clamp: (2) 1.5" x 1.5" x 15" perforated angle iron
                 (2) 1/4"-20 x 13" threaded rods
                 (4) 1/4"-20 wing nuts and washers
      13" round or octagonal kiln shelf
      kiln shelf shards
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Firebricks: www.armilcfs.com, 1-800-565-0306
  (insulating firebricks, 2800 F, density 55, 2.5" x 4.5" x 9", straight)
---------------------------------------------------------------------------
REFILLING SMALL PROPANE CYLINDERS:
There is a connector that allows empty one-pound propane cylinders to be
refilled from a 20-lb. tank.  The cylinder must be completely empty, and it
must be cooled in the freezer before filling.  (Screw the connector onto the
cylinder before cooling.)  Attach the cold cylinder to the 20-lb tank.  Turn
the 20-lb tank upside down so that liquid goes into the small cylinder.  Open
the tank valve for exactly one minute.  The cylinders weigh about 14 oz. when
empty and about 2 lbs. when full.
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SPECIALIZED EQUIPMENT:
#4 Salamander crucible  $28
Armil firebricks        $92 for 25 bricks (minimum order)
Pyrometer (optional)    $115

SUPPLIES:
Akron RTV silicone rubber           $38 for 1.1-pound kit (2 cups of RTV)
Hallmark MPK pewter                 $110 for 20 lbs. (looks like silver)
Kerr SatinCast20 investment         $63 for box of six 4.4-lb. (2-kg) jars
Atlas Everdur silicon bronze #873   $118 for 42 lbs.
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INGOTS AND REMELT:
 It is not advisable to melt down a mix of brass-like items for casting.
The results will be unpredictable because some metals in the alloys can
separate when molten. Silicon bronze is a forgiving copper-based casting
metal.  Silicon bronze remelt (your own ingots) can be used without adding
any new metal as long as you do not combine it with unknown copper alloys.
----------------------------------------------------------------------------
                          BRONZE CASTING

  The RTV mold that was used for casting pewter is now used to cast a wax
intermediate form for making an investment mold for bronze. The bronze mold
must be able to withstand the high temperature of molten bronze, which is
around 2150 degrees F.

Please go to PEWTER CASTING, follow steps 1 through 9, and then return here.

10. When pouring molten wax into the RTV silicone mold, it can often be held
    together just using rubber bands alone, with no plaster outer casing.
    A casting in wax of the sunbather figurine made in the RTV silicone mold.

11. Crayons and jeweler's sprue wax have been attached to form the sprue and
    vents on the wax intermediate form. They were attached using beautician's
    hot wax.  An espresso styrofoam cup is used to form the pouring opening.
    The line on the cup shows the final level of investment. Going from the
    crayon on the head up to the surface of the investment will be a length
    of coat hanger wire. This wire will be twisted out after the investment
    hardens to form a third vent.

12.  The blue wax is sapphire, which is very strong. The brown wax is French.
     The long rods are sprue wax, which can be bent without breaking.  One
     brand of beautician's hot wax, "No-Tweeze", is shown.  Remove the paper
     from crayons before using them for vents.

     IMPORTANT: Weigh the wax intermediate with all the attached sprues and
     vents and record this weight.
     The bronze casting, before cleanup and with all of the sprues, vents,
     gates, etc. still on it, will weigh 9 to 11 times what the wax assembly
     weighed.  So at least that much metal must be melted for the casting.
     Any excess can be poured into the cornbread mold cavities.
     It is important to have too much molten metal rather than not enough!

13. Styrofoam, cut with an electric hot knife, can be used to form sprues and
    vents.  Use a speed controller to adjust the temperature.  Wax tools and
    an alcohol burner to heat them are shown.  Wax that has been melted in a
    teaspoon can simply be poured into any voids to fill them.  Smooth the
    area with hot tools or your fingers.
    Hot tools can also be used to fuse the wax art form with vent and sprue
    wax.  Sandwich the hot tool between the vent wax and art form, then pull
    it out and push the waxes together.  Hold the attached wax in place until
    the joint cools.

  ------------------------------------------------------------------------
14. Mixing Investment:

    Investment and water must be measured accurately. (See table below.)
    Always add the powder to water. Check the time!  Whisk for 3 minutes.
    Investment has an 11- to 13-minute total working deadline after touching
    water.  It starts out pourable, then becomes spreadable/spoonable and then
    becomes stiff.  Eight minutes after touching water is the stopping time
    for any spooning and spreading, or else the strength will be greatly
    reduced.
   --------------------------------------------------------------------------
 15. This step can be done two ways.  Read both A and B and select one.

 A.  Put screen strips in the bottom of the box around the form, but not
    covering the opening/base/stand. Spoon down a layer of investment so it
    goes under the form.  When the investment gets a bit thicker, spoon it
    over the form. It takes practice to determine when the investment is
    ready for this step. Put screen strips around the form as you go up, but
    do not let the screen touch the form.  (If screen touches the form, the
    casting may fuse to the screen and have to be ground away at the point
    of contact.)  And/or wrap chain loosely around the investment.  Let the
    mold set up untouched for 2 hours. Let it dry completely for several days.

    Skip down to Step 16.

B.  To minimize the amount of investment used, formable aluminum mesh used
    by sculptors can be shaped around the wax form like a basket. This mesh
    basket should clear the piece by about 1" or 2" all around and come up
    about 2" higher than the piece.  Wrap aluminum foil outside this shaped
    mesh basket.

    Place the basket with the foil outside covering open-side-down on a sheet
    of aluminum foil.  Mix up fresh plaster and spoon it and spread it over
    the foil about 1" thick. Wrap chain loosely around the plaster shell and
    let the plaster cure overnight.

    The intermediate form will be supported by the same stand that was used
    for supporting the master while making the RTV mold.  The supporting
    screw(s) must be in the pouring opening part of the intermediate form.
    Other support screws can be in other sprues or form vents when removed.

    Support the plaster shell in a box or prop it up with odds and ends,
    open side up, and remove the bottom foil.  Lower the intermediate form
    inside this shell so that it is 2" lower than the rim and clears the mesh
    by an inch or two all around.  Mix up fresh investment and pour it into
    the plaster shell, burying the wax intermediate form about 1" deep.

      This photo shows aluminum sculptor's mesh, the original figurine, a
    pewter art form (for visibility) held up by the support stand and the
    aluminum mesh basket covered with foil, ready for the plaster outer shell
    to be spread onto it.

16. After the mold drys completely, use a hobby knife to cut through the
    investment down to the wax intermediate form in order to form a
    funnel-shaped pouring opening. If a styro cup was used, just pull the
    cup out.

  WAX BURNOUT:
17. Cheap chimney bricks from a cement plant are stacked to form an
    enclosure, similar to the way the firebricks are stacked for the bronze
    foundry.  Regulate the flame to slowly reach a final temperature of 1200
    F. This is the temperature at which a short length of 3/16" or 1/4"
    aluminum rod will begin to droop if placed inside the oven horizontally
    in a coat-hanger-wire holder.  (Or use a pyrometer.)

    The chimney brick oven ready for burnout showing a pyrometer in use.

    The sheet of information that came with the investment said to ramp up
    the heat over many hours, but we found that that was not necessary.  An
    old electric kiln and the chimney brick oven were both adjusted to reach
    about 1200 F in under an hour and were held there for another hour.

    An old Paragon A-66, manual-switch kiln that was used for wax burnout.

18. See the FOUNDRY chapter to assemble and prepare the bronze foundry if you
    have not done so already.

19. Remember, you will need 9 to 11 times the weight in bronze that the wax
    form weighed in step 12 above.

    Wear a welder's or heavy denim jacket, heavy denim pants, face shield,
    heavy boots and high-temperature barbecue mitts or welder's gloves.

    Melt the bronze in the propane foundry. Turn off the torch any time you
    check the melt by looking down into the vent.  Use a steel rod in an
    extension handle to test the melted bronze. It should drip slowly off the
    steel rod. If molten bronze clings to the rod in a ball, it's too cold.
    If it all runs off quickly, it's too hot.
    Just turn the torch back on and it will relight itself.

20. After the melt is near the right temperature, turn off the torch.  Add a
    pinch of borax flux with a long tea spoon in the extension handle through
    the lid vent. Turn the torch back on. It will relight.  Let the flux
    accumulate impurities (slag, dross) for a minute or so. Adding a piece of
    clear glass will aid in the accumulation of impurities.  Turn off the
    torch. Now skim the slag with an expendable spoon in the extension handle.

    You can remove the lid vent for these steps. If you do, be sure to rest
    it on kiln shelf shards and NOT on concrete.  Turn the torch back on.

    Let the charge heat up again. Turn the gas off again to recheck it with
    the steel rod when it seems ready.  When it is time to pour, turn off the
    gas and remove the lid.  Rest the lid on the kiln shelf shards. Skim with
    an expendable spoon in the extension handle one last time.

21. Check that the crucible pouring lip is in the proper position.
    Check that your path is clear to the mold.

    Grip the crucible firmly with the tongs, lift it out, move it quickly
    to the mold and pour the bronze quickly and with minimum turbulence. The
    crucible lip should be very close to the pouring opening so as to avoid
    trapping any air as you pour. Pour the excess bronze into the cornbread
    mold cavities.

22. The flux and any metal remaining inside the crucible should be scraped
    out while it is still hot with a long tea spoon.  Hot flux is molten
    glass and will feel very thick.  Don't let old flux and metal accumulate
    in the crucible.

23. Allow the mold to cool completely, which can take quite a long time
    because investment is an excellent insulator.  After several hours, you
    can wet your finger and very quickly touch any exposed metal to check it.

24. Break open the mold and cut off the metal that was the pouring opening
    and any runners, vents, gates and risers. File or grind off any seam
    flashing and bumps.  Wire-brush and/or sandblast for the desired finish.

    This is our first bronze casting.  The face has been wire-brushed, but
    the rest is just as it was cast.  The right foot did not fill. There are
    tapped-gas voids on the torso.  Pewter needs few if any vents, gates or
    runners, and so we did not put any in the mold for this bronze test.
    Obviously, that was a mistake.

     Oops! If the figure is not what you wanted, cut it up, melt it down,
           pour it into the cornbread mold and try again.  Check the list of
           possible reasons for casting mistakes and make corrections.

    This is our fourth bronze casting. Proper vents were attached this time.

---------------------------------------------------------------------------

ADDITIONAL EQUIPMENT AND SUPPLIES FOR CASTING BRONZE:
     Equipment:                        Supplies:
     -------------------               ------------------
     firebrick foundry                 bronze ingots
     graphite crucible #2 or #4        brazing flux (welder's supply)
     crucible tongs                    investment (Gesswein)
     steel test/stir rods              brush for Vaseline or baby oil (only)
     weighing scale                    Vaseline or baby oil
     extension handle w/ clamp screw
----------------------------------------------------------------------------
Silicon bronze: Atlas Everdur (#873) 1-800-662-0143
Equipment & supplies:
Kerr SatinCast20 investment, Salamander crucibles, crucible tongs, etc.
1-800-243-4466   www.gesswein.com
-------------------------------------------------------------------------
 Mixing Tables for Kerr SatinCast20:
 (We could not tell any difference between the different mixes.)
                     (38:100)       (40:100)
  Water (fl oz)      Powder (oz)   Powder (oz)
  2                  5 & 1/4         5
  4                  10 & 1/2        10
  8                  21              20
  12                 31 & 1/2        30
  16                 42              40

 R & R UltraVest investment has a similar mix ratio and performs similarly:
  7 & 1/2  cups      10 lb     (makes 170 cu. in.)
  9        cups      12 lb     (makes 204 cu. in.)
  10 & 1/2 cups      14 lb     (makes 238 cu. in.)

NOTE: The instruction sheets that ship with the investments give certain
      steps for vacuuming it and for stepwise heating of it over many hours.
      We did not vacuum it and we heated the investment up to casting
      temperature in under an hour.
---------------------------------------------------------------------------
Densities:
 Everdur silicon bronze #873      .302  lb/cu in
 Hallmark MPK pewter              .266  lb/cu in
 wax                              .0365 lb/cu in

Casting metals:
Bronze (copper plus tin) melts at 1950 F.
Brass (copper plus zinc) melts at 1750 F.
Sterling silver (silver plus copper) melts at 1650 F.
Aluminum melts at 1200 F.
Zinc (pennies) melts at 800 F.
Lead melts at 620 F.
MPK pewter melts at 460 F.
--------------------------------------------------------------------------
BAD CASTINGS:
     While pewter is very fluid and thus very forgiving, the same is not true
  of bronze. Bad bronze castings can occur for many reasons:
      trapped gases could not escape during the pour
      the vents, risers and runners were not right for the piece
      the molten metal was not hot enough
      the molten metal was too hot
      edges of the mold broken off during the pour got trapped in the bronze

   When determining how to attach the cup-and-sprue, vents, gates and runners
(the names are confusing because in some books they are interchanged), turn
the piece the way it will be cast. (Upside down or rightside up.)  Look for
the way bronze will enter and where air could be trapped or if bronze would
not be able to flow into some pockets.  A vent must go from the lowest point
up to the surface of the investment.  Vents must also be put at places where
air will be trapped as the bronze rises and fills the mold. And bronze must be
able to get to all parts of the mold. The yoga figure was our most complicated
shape so far, and it required a sprue and five vents. (Most books refer to
"the sprue" as where molten metal enters the mold.)
  Keep notes on all mistakes and how they were corrected, with sketches and/or
photos.  Refer to the casting books listed below or in your local library.
---------------------------------------------------------------------------
TWO EXCELLENT LOST-WAX-CASTING BOOKS:
    For the casting of jewelry and small art works in precious metals and
 bronze is "Practical Casting" by Tim McCreight.
    For casting larger sculptures in bronze is "From Clay to Bronze" by Tuck
 Langland.
---------------------------------------------------------------------------
                 LOTUS YOGA POSE FIGURINE

   This commissioned piece, by the sculptor Svetlana Berzina, is done
in sapphire wax.

   This bronze casting from the above wax master was done in ceramic shell
by commercial bronzecaster Shawn Devaney and his team. It has been sandblasted
and the face has been wirebrushed.

  The bubble-wrapped bronze master, with threaded bolts soldered onto it,
supported inside the plaster mother mold.  All relevant positioning marks
can be seen on the plaster.

  The above plaster mold separated, showing the cavity that will be filled
with RTV silicone rubber around the bronze master.

  The RTV mold made in the plaster mother mold.

  The RTV mold cut apart.

 Note: The yoga RTV mold required several rubber bands to hold the seams
       together.  Straight pins were needed at some places. It was dusted
       with talc and is now inside this plaster-and-chain assembly.

  A pewter test casting made in the RTV mold as it first appears.

--------------------------------------------------------------------------
REINFORCING MOLDS:
  Many metal materials can be used to reinforce molds.  Metal mesh, bronze
screening and chain have already been mentioned. Heavy aluminum wire, steel
baling wire, coat hanger wire and plumber's strap are also useful.

--------------------------------------------------------------------------
   We cast this test bronze after our wax master was vented and ceramic-shell
coated for us.  The surface is very rough, there is an area of shrinkage
cracks in the lap and the vent on the foot was sized and placed improperly.
Ceramic shell must be heated to 1200 F before pouring the bronze.  A worse
drawback is that ceramic shell is much harder to remove than investment.

  Sunbather bronze shown in Photo 26 with the sprue and vents ground off,
wirebrushed.

  Our yoga lotus pose bronze casting as it first appeared.

  The yoga bronze cleaned and wire-brushed.

  This third yoga intermediate form is cast in French wax.  Two sprues are
formed of the same wax on the thighs, a sprue-wax vent goes from the head to
the surface of the mold and there are four small vents at the tips of the
hands and feet. It will be necessary to carve the investment down to one
sprue to form a pouring funnel, since no syrofoam cup was used. It is
supported by coat hanger wire inserted into the thigh sprues.

  Permanent steel flasks made for RTV rubber molds and for investment molds.

----------------------------------------------------------------------------
         Svetlana Berzina, sculptor
         P.O. Box 3811
         West Palm Beach, FL, 33402
         (561) 827-0859
         www.lakiagallery.com
----------------------------------------------------------------------------
          A NOTE ABOUT HOW-TO BOOKS, INCLUDING THIS ONE:
    I have written what so far has worked well for making small metal
art figurines in pewter and bronze and for making small castings in
bronze which were to be machined.

    Experiment. Keep a journal. Keep notes about every casting, the failures
as well as successes.  If you will be making several of the same castings,
your notes will be crucial for saving you time and wasted effort.

    You can discover your own easier and/or quicker procedures, ways to get
better results for any particular piece, less-costly supplies and equipment,
etc.  Nothing in any how-to book should ever be considered chiseled in stone.

     We had good results cooling our RTV molds before casting pewter in them.
But heating the mold in a kiln or wax-burnout oven may allow pewter to flow
better, releasing any bubbles and filling every crevice of the mold.

     A self-burning art material was tested.  Damp papier mache was
mixed with potassium nitrate, an oxidizer, which was worked into an art
master and then allowed to dry.  A mold of investment was formed over
this artwork. The master was then ignited with a match.  The composition
burned itself out of the investment mold, like incense or a cigarette burning
away. Only ashes were left, which were easily blown out, leaving a mold ready
for molten bronze.  But papier mache is not an ideal, pliable art medium to
work, compared to clay or warm wax.  So we didn't do anything more with this
medium.  Wax with an oxidizer did not work.  Perhaps you can discover a
medium which is easy to work and will burn itself out of an investment mold.

    A mold-drying and preheating oven could be placed on top of the bronze-
melting foundry vent to make use of that heat that is otherwise wasted.

    We tried investment molds at room temperature and heated to 1,000 F.
They seem to perform similarly.  Ceramic-shell molds must be heated to
about 1300 F before casting.  But ceramic shell has unique requirements and
is not recommended for the infrequent bronzecaster.

    We used Wood's metal instead of wax.  This unique metal melts at 160 F,
so it can be melted out of molds using a common kitchen oven.  Vents were
formed using steel rods touching the intermdiate form. These were pulled out
before melting out the Wood's metal.  But any Wood's metal remaining inside
left a dark splotch on the bronze casting that was very difficult to remove.

    We used "green" sand, composed of common sandblasting sand, 7% bentonite
clay and water.  This works and is much cheaper than investment, but leaves a
rough surface finish. It is usually used in two-part "cope and drag" casting.

    The propane foundry was also used to heat steel for forging knives, just
to try it out. But forging and heat-treating knife blades is a science and
art in itself.