Earlier this week I wrote about how to make silicone molds from charms. Now it’s time for the next step. How do you fill a silicone mold with polymer clay and get a good casting? It’s really a very simple process, but as these things go there are a few tips that I can pass on. So here’s my take on using silicone molds with polymer clay.
How to Pack a Silicone Mold with Polymer Clay
Silicone rubber is naturally non-stick and a mold release is not needed when using silicone molds. (Other molds, such as ones made from rubber, urethane, polymer clay or Sculpey Mold Maker, most definitely will need a mold release such as water, cornstarch, or Armor-All. )
You’ll need to start with well-conditioned clay. If the clay is stiff and cracks easily, the mold won’t be filled cleanly and you’ll have seam lines. When you have a lump of polymer clay and a silicone mold, it’s very tempting to just push the lump of clay into the mold. In fact, some silicone molds are called “push molds”. But if you do that, you will quickly find that the clay won’t always fill all the detailed areas of the mold. To get a high quality cast or mold with polymer clay in silicone molds, you might find these tips helpful. You can use commercially purchased molds for this project or you can make your own silicone molds from charms or even little toys you might have.
- Start filling the mold with little pieces of clay, making sure that you’ve pushed it down into the smallest and most detailed areas of the mold. You might find that the clay sticks to your finger and won’t stay in the mold. If so, just roll your finger off the clay, rather than pulling straight up. Once there’s more clay in the mold, it usually sticks better.
- Add more clay until the entire area is filled with clay. Remember that if the clay sticks to your fingers, roll them off the clay rather than lifting up.
- Once you’ve put in enough clay to fill the cavity, press down with your thumb or fingers to make sure all the bits of clay are fully fused together. If any parts come out of the mold, just mush them back down again. Don’t be shy, really give it a good mashing. You want to remove all the seam lines of the clay pieces.
- Use a blade to carefully slice off the excess clay. It’s better to take several shallow passes with your blade rather than one big slice. If your molded piece pulls away from the mold, just push it back in. Sometimes the drag of the blade can pull the clay out of shallower areas of a mold.
- To get the last little bits of clay, you might find it helpful to flex your blade into a U shape so that only small areas are being scraped.
- Use a needle tool to clean up any areas where the clay overflows the edges of the mold. Especially if the mold wasn’t fully flat, you might need to dig out some areas, such as the space between the bee’s leg and body in this example. Tip: You can make your own needle tools in a variety of sizes using darning and tapestry needles. My free tutorial is here.
- Once you’ve got all the edges refined, you might need to shave off some more excess clay with your blade. Use your fingers to gently “sweep” the edges of the clay toward the center, away from the mold. This ensures that there isn’t stray clay around the edges of your casting.
- Soon you’ll have a perfectly filled mold with a nice, flat back, ready for demolding. Also check that no stray bits of clay remain on the face of the mold.
Removing your Molded Polymer Clay from a Silicone Mold
Always let your clay rest a bit before demolding. This gives it a chance to firm up and cool down, making it easier to remove from the mold. A few minutes in the freezer will accelerate this process, but be aware that a cold mold (and clay) will attract moisture in humid climates, making it hard for the polymer clay to then stick to other objects or other clay.
If your molded piece is fairly shallow and doesn’t have a lot of fine projections, you may be able to easily remove the polymer clay from the mold by turning it upside down and flexing the mold. The clay might very well just fall out easily with no distortion.
If it needs a little more coaxing, it’s tempting to use your craft knife or a needle tool to try to pick it out. Try to avoid doing that, though, as it’s usually going to create a problem by distorting your polymer clay. One trick is to use a piece of clear plastic sheet that’s been cut from a sheet protector. Just smooth it onto the clay, adhering it. Then invert and try flexing the mold again. Use the extra “suction” power of the clay being stuck to the plastic to help pull the clay out of the mold.
If that doesn’t work, you might need to get tougher. Get a clean piece of glass or glossy ceramic tile. Invert the mold (and clay) onto the tile. Press down firmly over all areas of the mold, making sure to adhere the clay to the tile. Now try lifting the edge of the mold, flexing it as you pull it off, carefully checking to see if the clay is staying stuck to the tile.
But if you can’t get the clay out of the mold without distorting it, all is not lost. Many silicone molds are bakeable and you can go ahead and cure your polymer clay right inside of the mold. If you created your own molds with silicone mold putty, check the instructions to see what temperature that your molds can be baked at. Amazing Mold Putty can bake at 395°F(200°C), and Easy Mold can be baked at 400°F(204°C). Since polymer clay cures at temperatures of 300°F(148°C) or below, there is certainly no danger there. Some mold putties have different temperatures, so please check the instructions. For example, the lavender colored mold putty from Penni Jo’s Best Flexible Molds shouldn’t be baked above 275°F(135°C). If you’re using a purchased mold, though, please check the packaging or check with the seller. Molds that I recently purchased on Etsy are bakeable, but I know that some are not. Don’t assume, check first!
Making a Faux Cameo
Here’s another way to get the clay out of a silicone mold, and make a faux cameo in the process.
- Prepare the mold and fill with clay as above. Condition and roll out a sheet of contrasting color clay. Because my bee was black, I chose white, but you could pick any color you want.
- Place the sheet over the top of the filled mold and press down firmly. You want the sheet to make good contact with the clay in the mold. Make sure you press all areas of the design. Don’t press too hard, though, you don’t want to make the sheet thinner.
- Keeping the clay on the mold, carefully turn the whole thing over and place the sheet onto a ceramic tile or other glossy surface. Press on the silicone mold in the areas where the design is.
- Carefully remove the mold by lifting one edge and flexing the mold. Look underneath and make sure the clay design (in this case, the bee) is remaining stuck to the sheet of clay. If not, put the mold back down and press more firmly so the clay adheres better.
- Use a cutter the appropriate size and shape and center your design in the cutter. Remove the excess clay.
- You can bake this now, or you can brush it with mica powder for an interesting look. If you are using black and white for your cameo design, try using an interference color of Pearl Ex. It will give a different effect on the white vs the black clay. I used interference blue here.
- Bake and insert into a pre-purchased bezel. (Or make your own with clay and mica powder!) Scroll down to see the finished necklace.
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