Smoothing Clay?

I made a two part mold of a die makers hammer that was my grandfathers. My question is how do you get your clay so smooth building up around the master? I got mine reasonably smooth, but the silicon (Smooth-On OOMOO25) had clay stuck in it when I de-molded (see attached photo). I was able to wash most of the clay out but it was a pain! Cast parts came out just fine.

What is the secret?

Picture of Smoothing Clay?
Paige Russell3 months ago

Hi Priedlinger,

Your mold came out great! Love the woodgrain texture of the handle. :D

The easiest way to get a smooth clay surface for larger molds* is to add a rolled sheet of clay as the final surface.

You do this by tracing your model onto a piece of paper and cut it out so you have a positive template of the object.

(*I just used my fingers and a lot of patience to smooth out the clay around my small donut model.)

Then, using a wooden dowel or a straight sided wine bottle (NOT the kitchen rolling pin) and some 1/2" - 3/4" risers (see how I made fruit leather in my Canning & Preserving class) roll out a sheet of sulfur-free modeling clay onto parchment paper, that is the shape your mold walls will be, but just slightly smaller (by 1/4" all the way around).

Then place the paper template of the model IN REVERSE onto the sheet of clay in approximately the same place it sits within the drawn lines of the mold walls. Use a sharp knife or exacto blade to cut out the shape, making the cutout 1/4" bigger than the object. Set aside.

Next, build up a foundation of clay on the mold board around the model until it is 1/2" or 3/4" (whichever height your risers were) below the part line. You don't have to worry about getting this first surface very smooth.

Then flip over the rolled sheet and gently lay it down onto the clay foundation, lining the model cutout up with the model itself. Peel off the paper.

Then all you have to do is roll out some snakes of clay to fill in the spaces between the clay and the model and mold walls and add your keys.

To clean the oil based clay off of your molds, use a small stiff bristled brush and warm soapy water.

I hope this is helpful for next time!