Process for Silicon Mold to Wax


A few weeks later and everything is off to the foundry for rough-casting! I just need a purge-valve for those last few weeks so my “kill kill kill” meter zero’s out: with our bad smog here in SLC it is still pinging away at redline.

The three figures show distinct stages of silicon mold. The far L has a seam line added (seams are cast in a mold created just for the seams and applied with T-Pins and a layer of fresh silicon as glue). The middle has a strengthening layer of cloth mesh. The R has a final layer of silicon and is prepped with spherical keys and fin keys (waxed paper cups held in place with T-pins with tape sealing the pins) for the plaster mold.


Here all three figures are ready for plaster mold. Now I clean up all silicon process and begin prepping for plaster layup. I cut hemp fiber till I pop a blister on the top of my fingers, and repeat this again and again till I can’t feel it anymore. I have a great little silicon mixing bowl from a specialty kitchen store that I mix the plaster in and can shatter out any remains. I also recommend a small wet-mix blade for the power drill- this airless agitation helps the plaster set up faster.


I do three layers. A wet impression layer, similar to a flick-coat. A well pressed layer of plaster/hemp capturing all undercuts. A final plaster/hemp layer. Then I create ridges of plaster/hemp anywhere additional structural support is useful.  The trick is to keep it as light as possible. When it has set overnight or longer I drill out the fin keys for bolts & wingnuts at a standard 1/4 x 20.


The plaster mold seam is ground clean with a flexible-shaft tool and a big grinding head that won’t bind up with plaster. I usually have a bag of small wedges for prying & coaxing the plaster away from the internal silicon mold, but they had disappeared so I used a cat’s paw and a small prybar and controlled monkey-strength. I snapped the molds in a few places, but just mixed up more plaster/hemp/swears and fixed it. I also tore a few key-spheres away from the silicon. IMG_0010

Here the plaster is separated, but how did that silicon mold separate? I create a seamless mold, as explained in the previous post, so the silicon must be painstakingly cut apart in a maze of zigzag  square bladed exacto-knife cuts. This part requires another pair of hands, and E helped me for two solid days of her three-day MLK weekend. The constant hard pull to separate the silicon seam agitated her old whiplash and my old broken ribs. We are gimpy old farts at 45.


The molds made an overnight trip down the highway letting the foundry pull the wax, and it was back to the studio for wax chase. I made a rookie mistake and overtightened the bolts holding the molds together, which skewed the molds off register here and there- just enough to nearly bankrupt the entire endeavor. I am on a tight deadline for casting and can’t take more time for an additional try at better wax forms, leaving me to re-sculpt in wax using the magic of swears, heat guns, sandpaper & lighter fluid, zen meditation, samsara, swears, and many more books on tape. For some reason the male figure’s hand/ball had collapsed, requiring that I pull that area again, cut off the disfigured area and add the new bit in place with the heat of pathological overpatience. Two days later they were back at the foundry for rough-cast.

We will see them again in 3 Mondays, and if all goes well they will be in lots of bronze pieces for me to weld together.



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