Monthly Archives: March 2007








This is a familiar process for those who have experience in silicon molding, but I have picked up a few refinements that save great amounts of worry and labor. Picts will get rotated correctly someday…

Silicon Mold
    Silicon mixes 10/1 with catalyst.
    Weigh with postage meter in plastic bag, or triple beam.
    Sport Mesh
    Vynil Gloves & Respirator Mask
    Knife, Spatula
    1″ dollar brushes- natural bristle

    Impression Layer: plain silicon painted on for detail.
    Layer Two: silicon & optional dye for layer id & cabosil added for peanut butter consistancy- batches of 300g silicon to 30g catalyst, with 1/4-1/3 cup cabosil; mix the cabosil in after mixing the silicon/catalyst.

    Layer Three: silicon & cabosil at peanut butter consistancy

    Mold Seam: silicon & cabosil (add dye) till pie-crust consistancy- add all cabosil at same time, then stir till                     stiff. 1.5 cups of cabosil to 500g silicon. Max width of seam at 3/4″, build to 3/4″ height. Backfill undercuts.

    Sport Mesh: Pre-cut mesh into piles of variouse sizes- long strips, squares, etc.
        Spread peanut butter consistancy silicon, then press in the mesh- can leave Mold Seam un-meshed.

    Cover Layer: Silicon & cabosil to peanut butter consistancy- cover all sign of mesh.
    Mother Mold: shim with photo plate/thin aluminum- usually free from a local printer. Using 1.5″ sections of welding    rod, or other pin material- pushe the pins into the mold seam as needed to support the shim and tape in place with regular “scotch tape”. Also tape any gaps between the mold and the shim, and shim seams.

There are many possible mother-mold options. Plaster and Hemp is cheap and quick but heavy; Fiberglass is a great option for low weight and flexibility/forgiveness of undercuts. The foundry has a unique method of spray-on foam- although I don’t think it is viable without their special foam hopper. The store bought expanding foam won’t lay on well and isn’t of the same strength.
Spray-on foam: this is unique to the foundry as it requires a foam hopper that mixes two part expanding foam- foams can be of variouse density and rates of expansion. It is a $10k machine. A drawback to the foam mother mold is that it insulates, so pulling a wax takes longer as the hot wax chills slowly. The mold is amazingly light and strong. Prior to foam, clamp 1/2″ wood supports to the aluminum shims for pinning the mold together- these will be drilled through for bolting the mold together tightly.

    Split Mold Seam: Cut foam back along seam to line of aluminum shim. Pop apart with wooden wedges and a mallet. Remove silicon mold from mother-mold. Separate silicon mold along seam using self-keying technique via small zig-zag cuts with exacto-knife. This technique allows the mold to lock together without the use of mold keys. It is helpful to have another pair of hands for this.     

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