Using Silicone Molds with Polymer Clay

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.

Learn how to use silicone molds with polymer clay to make faux cameos, charms, and much more in the this article from The Blue Bottle Tree.

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. )

blob of clay makes poor mold

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.

  1. Use bits of clay to fill the mold, rather than one large blob.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.
  2. fill the mold with bits of clay so that all areas of the cavity are filled with polymer clay.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.
  3. Once the details are filled with polymer clay, fill the rest of the cavity and push to make the clay fuse together.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.
  4. Use a long blade to remove excess polymer clay from the back of a mold.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.
  5. Gently shave the excess polymer clay from the mold with a blade.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.
  6. Use a needle tool to clean the edges of a complex mold, pushing the clay back to make a more clean mold.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.
  7. After refining the mold, use a blade to remove any excess polymer clay.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.
  8. Here is the filled mold, all cleaned up, ready for demolding.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.
Shallow and simple molds of polymer clay will easily demold, or come out of the silicone mold.
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.

You can use a piece of plastic sheet protector stuck to the polymer clay to help with demolding from a silicone mold.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.

For a tenacious mold, press the polymer clay to a glossy ceramic tile to help adhere the clay. Then lift the silicone 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.

  1. Put a sheet of clay over the mold.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.
  2. Press on the sheet to adhere the clay sheet to the clay in the mold.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.
  3. Turn the mold over and place the sheet onto a ceramic tile.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.
  4. Demold by lifting the silicone mold.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.
  5. Find a cutter that is larger than your molded piece.Use a cutter the appropriate size and shape and center your design in the cutter. Remove the excess clay.
  6. Faux cameo of a polymer clay bee.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.
  7. Bake and insert into a pre-purchased bezel. (Or make your own with clay and mica powder!) Scroll down to see the finished necklace.

Love Polymer Clay?

If you love polymer clay and are eager to learn more, don’t miss my Favorite Articles page. There you’ll find a list of my most popular articles about topic such as Baking Polymer Clay, Using Sealers, products reviews, and even an article about the 10 Sculpey Mistakes you don’t want to make. Head over there now!

Here's a quick directory to the favorite articles from The Blue Bottle Tree, the polymer clay information and tutorials website.

Learn how to make this bee faux cameo in polymer clay with silicone mold putty.
Here’s one way to showcase the faux cameo I just made. I found this bib necklace, missing the center, in a bargain bin at a department store.

 

Sources: I purchased the bee and mushroom charms from Pink Supply on Etsy. And I bought the mythical god mold from Mold Stuff on Etsy. Had good interactions with both sellers, too!

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