Thread: mold-making
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Old 02-10-2013, 02:10 AM
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TankDan TankDan is offline
Join Date: Jan 2013
Location: MT
Posts: 310

Hello everyone,
I've got a question about making molds for resin casting. It seems that 2-part resin is relatively inexpensive. When one uses a kit like the Alumilite products, it seems that most of the expense comes from the cost of the RTV rubber for the mold rather than the resin itself.
I've attempted to make molds from plaster with little success, and even if one was to achieve a quality negative, a plaster mold would not last long. Perhaps a couple pulls at best I think, unless the part is bulky and very simple, lacking detail.
I have a BA in Fine Art, and to achieve that I had to take some sculpture classes. In these classes we did numerous types of casting, ranging from an intro to resin casting, but we actually had to make bronze castings using the lost-wax investment technique, and we did aluminum casting using displacement techniques.
The first step in the investment technique, after the master was formed, was to literally paint silicone rubber over the master (using Pam cooking spray as a mold release). This served as a detail layer, picking up the finest details down to fingerprints and even specks of dust. Our masters were made of oil-clay...quite literally clay made using motor oil instead of water.
After the top, painted on layer of silicone was cured, we added strength to the mold by squirting globs of silicone into our hands and dunking it into a bucket of very cold water, and kneading it into a ball. This served to make the silicone almost clay-like, and it could be applied to the master in a very thick layer. It would bond to the painted-on layer, and provide some structure and strength to it.
After that we moved on to making a plaster shell for the silicone rubber mold to provide more strength and stability to the jiggly rubber mold. I wont go further into detail of the process, but I have a question. Has anyone tried using a house-hold silicone rubber for mold making, or even something like Perma-Seal RTV? Using the technique I've described above, a mold could be made quite inexpensively compared to hobby-quality RTVs, and with as good of detail pickup. It is just as reusable, and far more accessable. Does anyone forsee a conflict of materials, such as styrene (assuming your master is made of styrene) and house-hold silicone, or the resin and the silicone? In other words, whats so special about hobby-grade RTV that makes it so expensive?
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