Silpak, Inc

Hello there,

Ive got a dilemna thats been driving me nuts. I want to transform an object using clay, then make a mold of it to cast in resin. The problem I have is in choosing between two precarious routes: 1) I build on the initial object using a non-drying clay so that I can get good adhesion without cracking or shrinking. (I also foresee this as providing a more seamless addition to the initial object ) but the downside is that I wont be able to brush on silicon without affecting the clay underneath. Alternatively I go for 2) Use an air-hardening clay so that I can brush silicon on without fear of damaging or distorting the clay but will it shrink, crack and make joins between clay/object visible.

Thanks for listening.

Is it a part the could be slowly dipped in the silicone for the first layer?

Hello there,

Thanks tremendously for your help.

I would worry that the pressures of both pushing it into the thick, sticky silicon and retracting it would result it some distortion of the most vulnerable regions of clay and that the join between clay and plastic part would be in real danger of coming apart. Retreival from the pot of silicon would be impossible so this would be a very dangerous operation after hours of sculpting the clay. Is it possible to build layers of silicon? Ive only ever poured it over parts, repeating with the same batch every half-hour until it is barelty pourable / scoopable.

Thanks again,

All the best

If your original object is fairly rigid, you could use a hard plasticine such as Chavant NSP Medium or Hard grade. They can be molded by hand when slightly warmed or can be worked with common sculpting tools. They are firm enough to withstand careful handling or brush strokes without deforming. They are used all the time in the FX industry under plaster, resin, or silicone. Use a soft brush and carefully brush on a thin coat of your silicone getting it into all the details. You can then add a thixotropic coat or two to build thickness.

If you pour a block or matrix mold, you can find relatively low viscosity silicone that still sets up to an appropriate durometer.

Be aware that some plasticine clays contain sulfur which can cause curing problems with platinum (addition) silicones, but not tin (condensation) silicones. Most sulfur free clays are clearly marked. Chavant NSP stands for Non-Sulfured Plasticine. There are many other sulfur free clays. If you have a silicone picked out, ask the manufacturer for a recommendation.

There are also waxes used for sculpting that come in grades from very soft to so hard you can machine them with power tools. These might also work, depending on your particular application.