1) PROTOTYPE
Your original piece should be a solid, nonporous piece made of wood, fimo (sculpy), metal, or anything else that is not soft or easily distorted.

2) THE BOX
Make a box that is slightly larger than your prototype. A box that is too big will waste material, too small and the mold walls will be too thin. Watertight.

3) WAX BASED MODELING CLAY
Fill the bottom of the box with wax based modeling clay. NEVER use plastalina style clay! It is not compatible with silicone rubber and all will be lost.

4) PARTING LINE MANIPULATION
Bury the prototype half way in the clay. You can build clay up (or remove from) certain parts of your prototype to create an advantageous parting line, different from a flat, linear, arbitrary line like you would get if you just pressed the prototype into the bed of clay.

5) HEMISPHERIC REGISTRATION
Take 2 marbles or ball bearings and press them halfway into the clay at diagonal corners of your box. Eventually these will form a ball & socket to align the mold halves easily.

6) IVORY SOAP RELEASE
A bar of IVORY brand bar soap, shaved and put into a 10% solution with warm water is a terrific release between stuff and liquid silicone rubber.
Brush it on and let it air-dry. Silicone mold release does not work.

7) RTV 3120 MIXING TECHNIQUE
As you handle the rubber, use exaggerated care not to introduce air. Spoon or pour the rubber into a paper cup, add catalyst and mix GENTLY. Then, after 120 seconds of gentle mixing, change to a new cup and mix gently for another 120 seconds. The catalyst ratio is 1:10 (ten parts rubber to one part #1 RTV
catalyst). I use the paper cups with graduations. Observing the mm/cc scale you can usually eyeball 10% by volume. As added insurance, I keep my rubber warm while curing (77oF. or better) to help things along.

8) POURING THE FIRST SIDE
Pick a spot in the box and pour to that spot only. Let the relative level of rubber rise and flow over the box contents. This traps less air than pouring all over, like syrup over pancakes. Pour beyond the top of your part to the desired wall thickness. Usually 3/16” to 1/4”. Allow to cure in a warm, dry place for 24 hours minimum.

9) CREATING THE SPRUE AND GATES
Empty the box and remove clay and marbles. Place the rubber side down back in the box and adjust your prototype to fit snugly in the rubber bed. Using wax based modeling clay, shape a large funnel leading from the wall of the box and tapering down until it contacts the fill point of your prototype. If your configuration requires gates or runners, make little clay snakes and lay them out now. Pewter shrinks as it cools, a large sprue can bear the brunt of shrinkage and protect your piece from undue distortion. It costs nothing, since the sprue is instantly and 100% recyclable back into the pewter pot.

10) IVORY SOAP RELEASE AGENT
- AGAIN Apply as before to the inside walls and contents of the box. Let air dry.

11) POUR SIDE 2
Mix and pour the RTV 3120 as before. 24 hour cure.

12) DEMOLD
Remove from box and carefully separate mold halves. Check to make sure that the process has been successful. Store mold halves together with mold supports
on the outside and wait for a couple more days to let the mold mature before casting pewter.

CASTING PEWTER IN SILICONE RUBBER MOLDS

1) EQUIPMENT SUGGESTED
#1903 Melter, #1907 Ladle, #1919 Pony spring clamp, #T-42 Talc, #662 Flush Cutter, #T-AP mold supports, spoon, ashtray.

2) MELT THE PEWTER
Set the pot at around 5.2 for silicone molds.

3) DUSTING TALC
Dust both mold halves with talc. Clap them together like chalkboard erasers.

4) USE ALUMINUM SUPPORTS
If you can, use aluminum supports. The aluminum acts as a heat-sink and reduces the time of heat exposure that the silicone must suffer. Put dusted mold halves together, aluminum supports on the outside, and clamp together.

5) SPOON OFF DROSS
Using a common silverware spoon, scrape the carbonization off of the molten pewter surface in the pot. Tap it into the ashtray for further reclamation.

6) POURING PEWTER
Immediately after cleaning the surface, ladle up a portion of molten pewter and pour. Fill the sprue entirely. Watch as the surface in the sprue hazes over as the metal solidifies. Careful: Fresh piece is hot! Nip sprue with flush cutters.