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 articles category. 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!

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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!

44 thoughts on “Using Silicone Molds with Polymer Clay”

  1. Hi, noob as far as the polymer clay crafting goes and had a question I was hoping you could answer. I’ve looked online but haven’t found any good hints as to how to make a two part mold (front and back) that fit together to mold a complete object from silicone strictly for polymer use. I understand how the process is done as far as plaster- but given the different states of flow, clay being far thicker obviously, this method will not work. Any help anyone can give on this subject is appreciated.

    1. Unfortunately, I don’t know very much about this. Typically, silicone mold putty is not used for two-part molds. It’s normally used as a push-mold, where things are pushed into it. For two-part molds, they usually use some sort of casting material like plaster and the process takes several steps. There is much more information about the various types of molds and molding materials through the folks at Alumilite. https://www.alumilite.com/store/pg/21-How-To-Videos-Alumilite-Mold-Making-Casting-Materials.aspx

  2. Joel Acevedo

    I made a mold with sculpey. When I add the clay, it stick to it. Do I need to do something before adding the clay?

    1. Yes, you will need to use something to keep it from sticking. This is called a “mold release”. We typically use a quick spray of water. Or you can dust the mold with cornstarch. Either will keep the clay from sticking to the baked clay mold.

  3. Nika van Tilburg

    I recently bought a mold that I love: great detail, perfect size EXCEPT that the finished pieces are too thick for my purpose. I tried taking one of the cured pieces and making a shallower mold but couldn’t reproduce the detail the silicon mold creates.

    Is there some way to cut the silicon so I get the detail in the bottom of the mold but a thinner finished piece? Or can I use a jeweler’s saw to cut the cured pieces to the thickness I desire?

    Thanks very much for any suggestions. I have a lot of metal smithing experience but am new to polymer clay and not sure the best way to solve this particular problem.

  4. I am also a newbe to polymer clay. I enthusiastically purchased lots and lots of silicone molds. I’m OK with the one part type yippee! Thanks to your advise and guidance . The two part type however are proving an absolute nightmare. I’ve tried banding the molds when filling to stop distortion. I try to fill as cleanly ass possible but they either don’t marry right or leave a thick Ridge that the novice i am cannot smoothe awayou without a mess. Feeling very disheartened after many hours producing nothing boo!

    1. The issue is that the volume has to be EXACTLY right to fill the mold. Too little clay and you have empty spots. Too much clay and you have excess clay squishing out at the seams. You will have to experiment greatly to get the correct volume of clay. And then you have the issue that it’s impossible for the clay mass to move from over-filled areas to under-filled areas when you put the two pieces together. Polymer clay doesn’t flow in the same way a liquid would.

      Even then, however, there will be a seam where the two sides come together. That will have to be removed by hand, preferably before baking. Molding is a lot of work and can often be more complicated than just sculpting it from scratch.

  5. I am brand new to polymer clay. I found your tips to be very helpful. But I can’t find an answer to my current problem. What causes my clay to crack in molds? I promise I’ve used all your tips for filling the mold but I find it cracking before I even cure it! Then the ones that ‘appear to be ok crack after curing. I use the Sculpty brand of clay. And I love it. The beads of my own making turn out fine. It’s those darn molds!! Help Help!!!

    1. There’s no reason that clay will crack in molds, specifically. It sounds like it’s not a mold problem, but a clay problem. You say you’re using Sculpey (there’s no “t”, btw), but that is a brand name and there are several clay brands under the Sculpey name. Some (such as Original Sculpey, Super Sculpey, and Sculpey III) can be quite brittle after baking. Switch to Premo or Souffle to get better results. If the clay is breaking before curing, however, that sounds like the clay old (crumbly) or is not getting conditioned well enough before you put it into the mold. Try mooshing it in your hands first. Work with it until it’s smooth and sticks together well. Then fill your mold.

  6. Can I make a silicone mold of a silicone mold or will they stick to each other? For example in the case where the “prototype” is already a mold, but not polymer clay or oven safe?

  7. Thank you so much for this info! I just bought a silicone mold and had NO idea how to use the polymer clay with it. This is a great start for me! 🙂

  8. Pingback: How-to: Using a Mold and Making a Cameo from Clay – Polymer Clay

  9. I have the opposite problem. I bought a silicone cameo mold with lots of intricate detail and I can’t get the clay to stick! When I’m trying to fill the cameo, I cannot for the life of me get the clay to stick to the mold and stay there! I have tried pressing it, smearing it, freezing it, and doing tiny bits of clay at a time but I just can’t get it to stay in there! Any ideas?

    1. Some molds are so shallow that the clay really has trouble sticking in there. First off, give the mold a good wash with soap and water to remove any excess oils on the surface. You don’t want it too non-stick. If the mold is just too shallow, then you’re going to have to fill it with exactly the right amount of clay so that it will be exactly filled and there’s no overage to cut off. It’ll likely be a bit of trial and error, but when you get it right you can press it down with a ceramic tile to get a flat back. Remove the mold and you can bake the cameo right on the tile.

    1. Actually, I debated writing about that in the article. Just follow the same steps to fill the molds. Except that you can’t slice the excess off the back, obviously, so you have to make sure to not fill the molds with more clay than will fit in the little cameo part. Less is more! Needle tools will become your friend, too. Using the tools to clean up the edges of the cameo design is imperative. Then once you get it just the way you want, you need to fill with the background color. Just make a smooth lump the same size and shape as the rest of the cameo mold and place in into the mold. Press gently and slice any excess off the back just as in this article. Then demold. It takes practice, of course, but it can be done!

    1. I love all the good comments I get on posts. People are so good to share their ideas and contribute their experience. We’re very much a community and that helps us all!

  10. Thanks for another great post! 🙂 I also like to brush my molds with a super light layer of baby powder first to work as a little extra insurance plan to prevent any possible sticking. ( And then I just brush the powder off of the cIay when it comes out of the mold) I like to let the soft clay set up in the mold before I trim away the extra clay with the tissue blade-makes for a cleaner cut and I don’t wind up trimming off any small, soft details or distortions in the clay~ Thanks for sharing Ginger! you’re as FABULOUS as always!!

    1. Oh gosh, I have the opposite problem, some of these silicone molds are so slippery it’s hard making clay stay in them! But if powder works, then so be it! And I’m glad you mentioned letting it rest and set up before slicing off the back. I should have thought to add that. But you know me…impatient!! I’m always eager to get on with the next step of everything. Thanks for the kind words, Elizabeth, you’re the best!

  11. I bought some silicone mold material a while ago, and have yet to use it… your last post and this one were great to see before digging into it. Thanks for the thorough information, it’s helpful as always and much appreciated!

  12. I wondered about piecing the clay into a mold and decided not to chance messing it up. Now I will try it! Thanks Ginger. And yes on having to use something to get clay out of the Sculpey mold maker. I learned that one fast. lol

    1. If you don’t push hard enough (once they clay’s all in the mold) or if they clay’s not real well conditioned, you can still get seamlines. But it’s really the best way to get clay down into tiny places like that bee’s legs. Molding the mushroom, I would probably wouldn’t use as many pieces…it wouldn’t need it.

  13. I’ve also waited to trim the excess off the back of the mold for a couple of hours. Particularly if it’s warm. The clay seems to ‘set’ just a bit, making it less mooshy and easier to cut.

  14. Great information Ginger! Thanks! I use silicone molds all the time with metal clay, but it helps to see how differently you fill them with polymer clay. There’s always something new to lear. As others have said, you explain it very well.

    1. Thanks Barb. There are so many ways to do everything, this is just my little way. When people are new, it really helps to have a guide and that’s why I wrote this, but we all learn our own ways that work for us. I bet I’d learn a ton from you as well!

  15. Another terrific post. I have been claying for many years, and always find something informative or a good reminder of something long forgotten in your posts. Your write clearly, and with a lovely combination of “do it this way” and “it really doesn’t matter”. Wonderful!

    1. As always a very informative article. IWhen I get time for my clay work I do use molds and your tips have given me an answer to a few problems I have had.
      I use the freezer especially in summer as the clay gets too soft otherwise, but I leave it out to get back to room temp while I do something else and only ever leave it for a few minutes to get hard. I do like your cameo tip as my molds are often attached to a back( in effect a cameo although I never thought of them that way)
      thank you for this tip.
      I look forward to your next wonderful posting.
      Cheers
      Lynn

    1. Yes indeedy! It does most certainly work well. However, a caveat. I learned a long time ago that chilling polymer clay doesn’t work so well for me when it’s humid. And it’s humid here a lot. The minute that cold clay hits the air, it’s instantly covered in moisture. And wet clay won’t stick to anything. So I tend to think of freezing as a last resort. Yes, it does dry fairly quickly, but it creates its own set of issues, too.

      1. Could be that the way I work the moisture created by freezing is irrelevant. It’s 100% humidity here too a lot in the summer. If if were a huge issue, I would just put a tiny fan on them for 5 minutes. It makes colour application on raw clay easier too – firmer, especially in the summer. What issues outweigh the advantages of being able to remove the polymer cleanly and efficiently from the mold? Dust? Hairs?
        Oh my, I just overcooked my latest project – set the oven wrong…..been a long time since I’ve done that!

  16. Helpful as ever. Until I read this, I thought I knew how to use molds. Now I know why my casts were often distorted. Must practice patience and let things rest. Thanks for the tips.

    1. Thing is, sometimes a distorted mold is okay. It just depends on your purpose. If I’m using several molded motifs that I’m going to integrate into a sculpted scene, I might not care if things are this precise. But on the other hand, when I do want a precise mold, it does help to know how. I’m glad this gave you an “Ah-ha”.

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