Back at the World Con in Chicago in 1982, I picked up an
Imperial disk in the dealers room. Now, some 19 years later, I am
building some new costumes and needed some new disks. Since I have
done a lot of pewter casting, I choose to cast new pieces in pewter ( using a Silicone RTV mold ) rather than turn
new ones on a lathe. The pictures below document the process I used
to make the new Imperial Officer disks in pewter. I also have a listing at the bottom of the
page for the suppliers I use.
IMPORTANT SAFETY
NOTE:
I DO NOT USE LEAD based pewter alloys, NEITHER SHOULD YOU! The
toxic effects of lead in pewter alloys (especially on the young) are well documented.
Don't take a chance with your health.
While lead based alloys of pewter have been used historically, there is
no reason to use lead based alloys in this day and age. I currently
I use an pewter alloy called OR-8, it is a tin, antimony, and copper based mix. OR-8 has great strength and flows well into detail. As a side note, OR-8 is also very close to the pewter alloy also known as " Britannia Pewter ". There
are a number of "non-lead" pewter alloys available, so experiment and find the
one that works best for you. Also, keep a notebook of your
pewter casting projects. It helps you to keep track of what did and did not work
well while casting and what you did to solve it. |
Pewter Casting and Silicone RTV Mold Making Equipment |
Safety First - Pictured are some of the
"Tools of the Trade" used when casting pewter . I always wear at least a dust mask.
While the pewter alloy I use does not "fume", the dross particles (the scum you
get a the top of the pot) can become airborne and get inhaled.
Though small and non toxic, you really don't want them in your
lungs. Gloves and safety glasses protect your hands and eyes from
spills of molten pewter (if and when they happen). Be safe and you
won't be sorry. I also use a vent hood to help pull any
pewter dross / particles out of the work area.
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Silicone RTV and catalyst for creating the Imperial Officer " Disk" mold. These can be bought at a
mold supply or special effects supply store. |
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A gram scale to measure components. You can buy them
for about $30 at cooking supply stores. This one was bought at
Williams and Sonoma (spelling). It is accurate to 1 gram. |
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My smallest (2 lb) Lee melting pot, ladle, and lead
thermometer. These items can be bought at most gun supply stores. |
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A shot of the lead thermometer I use to track the
temperature of the metal. The RTV silicone will take over 600
degrees. However, it will degrade quickly at higher temperatures (it
turns to a Jell-O like consistency). The thermometer costs around
$30, but it is worth its weight in gold.
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The Pewter Casting Project ( Imperial Officer Disk ) |
Pictures of the Original - Here are some images of
the original Imperial Officer disk that I bought in 1982. It looks like it was turned in
aluminum and is drilled to accept a small machine screw. |
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Making a Silicone RTV Mold ( 2 part mold )
I used a two part silicone RTV mold
compound to create the gravity molds I used for the project. While
spun molds can be used, I am not currently set up to do them. Mold
Number 1 (the rightmost mold) was an unsuccessful two-part mold.
It poured vertically from the top edge of the medallion. The metal
"chilled" too much in pouring and the edges/ridges nearest the top would
not cast nice and sharp. |
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Creating the Mold with non-sulfur clay. The RTV will
not cure correctly if you use a clay with sulfur in it. |
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The finished mold box for Mold 1. Make sure to seal
all edges or your silicone will quickly show you where your leaks are. |
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A shot of the mixed RTV. The scale is "zeroed" with
the cup in place. The Silicone is then poured in and then the proper
amount of catalyst is added. (The knife is not left in when checking
weights for the RTV and catalyst). |
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I first brush in a layer of RTV directly against the
model. This helps to eliminate air bubbles in the surface of the
mold. I then pour in the rest from a corner (slowly to avoid trapping
air) |
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After the first layer cures (about 8 hours), remove the
first layer of clay, add mold release (VERY IMPORTANT), rebuild the box
and pour in Silicone RTV to cast the second side. If you don't use mold
release, the Silicone RTV will fuse with the first side, making it very difficult
to get a clean mold line (you can cut it by hand, but what a pain).
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After the second layer cures (about 8 hours), you can strip away the
clay, carefully open the mold, and clean it. You are then ready to
blacken/dust the mold and start casting. Unfortunately, Mold 1 just
would not cast the upper most ridges of the disks. While I did work
with Mold 1 to try to fix it (increased the size and the position of the
spru, raised the casting temp, changed the alloy used), it just would not
fill the upper edge of the casting correctly.
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Making a Silicone RTV Mold ( 3 part mold )
I then created a three-part mold (the
Mold on the left) that would cast the piece face down (helping
the metal to fill all the edges while still very fluid). It worked
much better and the castings from it come out nice and sharp.
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The mold box for mold number 2, I used Plexiglas side
walls to show a different way to build the mold box. Again, makes
sure to seal all of your edges or the silicone will drain from the mold
box.
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Brush in the first layer of RTV with a brush. I use
the brush to make sure that the layer of RTV next to the model fills in
all cracks and crevices of the model. This also helps avoid trapping
air bubbles next to the surface of the model.
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The finished three-part mold. I molded the top half
in one piece and then created the spru. I then cut the top part in
half (to allow the spru to release). |
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I use graphite to dust/blacken all of my RTV molds for
pewter. To blacken the mold, spray in a bit of graphite powder and
brush it in to crevices of the mold. Then rub it in with your
fingers. I normally blacken the mold every five castings. The
dusting/blackening of the mold helps you get an almost mirror finish right
out of the mold. If you don't dust the mold you get weird little
pits/bubbles on the surface of the mold.
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I sealed/closed the mold using rubber bands. I have
also used wooden frames and clamps on other molds, but the rubber bands
work well on this one. Be careful if using rubber bands, if molten
metal gets on them, they will disintegrate and release part of the
mold. Always wear your safety gear and cast inside of a secondary or
tertiary containment tray/box.
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Voila, a cast pewter Imperial Officer disk with spru intact! If you cut
of the spru (the excess material) while it is still warm, the pewter cuts more
easily.
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Here is one of the cast pewter pieces with the spru cut off.
Notice that the finish is very bright without even buffing. It will
get brighter once it is buffed. Also, I made the second mold with
the center hole filled in the master. This was to help the upper
disk mold properly. The center recess is then drilled into the
piece.
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Some of the finished cast pewter pieces. The original Imperial Officer disk is in the
lower left corner along with its machine screw. Next is the back of
a finished pewter disk with a butterfly clasp. The two pewter disks on the bottom
right have machine screws inserted. The top two rows are finished
disks. I will be taking the best 3-5 disks from the top group and
use them to make what I call a "gang mold". The gang mold will cast
3-5 pewter pieces at a time rather than one at a time. In addition, the
pieces will be cast with the center hole, rather than drilling the center
hole in each piece.
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A before and after shot showing the front and back of a cast pewter Imperial Officer disk
before final sanding/drilling and the finished disk with the center recess
drilled (from left to right). |
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Another shot of some finished pieces. The left piece
has the butterfly clasp installed. The butterfly clasp is normally
used to mount the disk on hats or others soft items. The alternate
method of mounting is to use a machine screw (i.e. for a belt
buckle). I am working on ways to cast the screw as part of the disk,
but for now I will drill them and mount them using the machine screw (just
like the one I already have) |
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Links to Pewter Casting Suppliers |
Pewter (OR-8 alloy)
Conquest Industries
9915 Bell Ranch Drive Santa Fe Springs, CA
90670 Phone: (562) 906-1111 Fax: (562) 906-1112 Toll-free: (800)
368-CAST Email: sales@conquestind.com
<mailto:sales@conquestind.com>
http://www.conquestind.com/default.htm
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Silicone RTV
CASTINGS, A DIV. OF REB TOYS, INC. P.O. BOX
298 Eastsound WA 98245-0298 (360)376-3266 (8:30am-5:00pm pacific
coast time.)
For orders ONLY call: 1-800-346-0567 Fax: (360)
376-3280 http://www.miniaturemolds.com/mainframe.htm
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