Cornstarch or Baking Soda with Polymer Clay

Have you read of people using cornstarch or baking soda with polymer clay and you wondered what that was all about? Why would you use it? And which one should you use? Is cornstarch better? Or is baking soda?

Supporting Polymer Clay During Baking

Learn why you would use baking soda or corn starch with polymer clay. More at The Blue Bottle Tree.If you make a round bead with polymer clay, and put it in a tray to bake it, what keeps that bead from rolling around in the pan? And if you bake more than one polymer clay bead, what’s to keep them from all rolling to the same corner where they’ll all bake together where they touch? You need to put your raw clay bead on some surface that will keep them from rolling around. Some people use accordion folded paper. Others use polyester fiberfill or quilt batting. But another simple option is to place them all on a bed of cornstarch or baking soda.

If you’re making a flat pendant, for example, when you set it on a pan or tile it will have shiny spots on the back. You can use a piece of paper under your clay to prevent this. Or, you can just set the pendant on a bed of cornstarch or baking soda.

Irregular shapes that need a little support can be partly buried so that the powder will support them and they won’t droop during baking.

If you bury polymer clay beads in cornstarch during baking, it will help protect them from browning. Article at The Blue Bottle Tree.

Protecting Polymer Clay from Browning

Most ovens heat with an electric element that gets very hot and glows orange while the oven is heating up, or when the element cycles on to keep up the oven’s temperature. Unless you’re using a convection oven that circulates the heat, this direct radiant heat can cause your polymer clay items to toast brown even if your oven is set to the correct temperature! This is particularly a problem for light colored and translucent polymer clays.

To help prevent this color change, it’s really important to cover your clay during baking. One method is to completely bury your raw clay creations in baking soda or cornstarch while they bake. This will allow them to heat to the full temperature that’s required for a proper cure, and still protect them against the direct heat of your oven’s element. Do make sure, though, that you add a some extra baking time because it does take a bit more time for the heat to travel to the clay when it’s buried like that. I’ve written a whole series of articles on Baking Polymer Clay that will help answer many of your baking questions.

Which One is Better?

Cornstarch or Baking Soda with polymer clay, which one is better? To an extent, it’s just a matter of preference. Both will work well for the situations above. But there are a couple of things to keep in mind.

Removing the Powder

See, sometimes the powder you use will stick to your baked clay and you have to remove it. The simplest way is to just wash them in running water. Most of the time, it will come right off. But know that cornstarch doesn’t dissolve in water and can sometimes remain slightly embedded in the clay. You might need to give it a quick scrub with an old toothbrush. Baking soda, however, is water-soluble and will dissolve completely. This means you won’t have any residue.

Other Powders

Can you use rice flour, wheat flour, or other white powders to support polymer clay during baking? Well, you could. They would work just like cornstarch or baking soda with polymer clay. But the difference is they get gummy when you try to wash them off. Cornstarch doesn’t get gummy in water.  Other starches such as arrowroot, tapioca starch, or potato starch might work for this purpose, you’d just have to try it. But since cornstarch is so readily available, it’s what is commonly recommended. If you’re not in the US, cornstarch might be an unfamiliar term. It’s just the US term for corn flour. It’s what we use to thicken a sauce and it what’s used to starch laundry.

By the way, baking soda is also called Sodium Bicarbonate. It’s not the same thing as baking powder, which is baking soda with other acidic powders added. Baking powder will work, but it’s just so much more expensive that it’s better to stick with baking soda.

I’ve also been asked about using talcum or baby powder with polymer clay. Can you use it in the same way? Well, most baby powder today is cornstarch and not talcum powder as talc isn’t so good for babies to breathe. So check your label. If it’s cornstarch, sure, give it a try. But if it’s talcum powder you may find that it is too hard to remove from the baked polymer clay.

Using Cornstarch to Smooth Polymer Clay

While baking soda is kind of grainy, cornstarch is silky smooth. This quality of cornstarch makes it excellent for smoothing the surfaces of your raw clay before baking. When we form our clay pendants and sculptures, for instance, we often leave fingerprints. You can remove them by dipping your finger into some cornstarch and smoothing it over your unbaked polymer clay.

Don’t do a “scrubbing” action, though, or you could bury the particles of cornstarch into the clay and you won’t be able to remove them. There’s a fine line between “enough” smoothing to get a nice surface and “too much” smoothing that will give you a white coating. Try it, experience will show you the way.

You can use cornstarch or baking soda with polymer clay to smooth fingerprints.

Cornstarch and Baking Soda can Cause Leaching

Polymer clay is made with oily plasticizers that allow it to stay flexible and strong after baking. Those plasticizers, however, will leach out into absorbent materials. This is why it’s never a good idea to leave your unbaked polymer clay on a piece of paper or on a bed of cornstarch or baking soda for long. The plasticizers will leach out and leave your finished piece more brittle than it should be. After baking it’s not a problem, though, as the plasticizers are locked between the molecules of the plastic.

44 thoughts on “Cornstarch or Baking Soda with Polymer Clay”

  1. Kathy McCurry

    Great information, Ginger! I’ve tried both the baking soda and the corn starch and quickly put the baking soda back up in the kitchen shelf for the reasons you mentioned. The main problem I had, since I do mainly surface treatments, was that it was quite scratchy and marred the surfaces of my carefully created treatments. The baking soda is much finer, as you noted, and is much gentler to use, especially with the surface treatments where sanding and buffing afterward isn’t an option.

    However, as a learner/observer, there may be times when a little ‘roughing up’ or scratching of a surface might be just the thing to create a different kind of appearance. So, I should keep in mind that baking soda would work well as a potential creative treatment.

    Thank you!

  2. Claire Maunsell

    When you bake baking soda for extended periods between 250 and 300 degrees it can change colour slightly, and it becomes caustic. You will notice this if you wash off your pieces if you have used it – it will feel a bit slimy ( as alkalis will do) and it will sting if you have a cut or very dry hands. For this reason, I often use corn starch and baking soda mixed….it also makes a good aggregate, not too fine or coarse.
    Interestingly, this baked baking soda may also be used in home baking to give pretzels the characteristic ‘pretzel’ flavour. A solution of water and the baked soda is mixed and the pre-formed pretzels are dunked before baking. Commercially, a stronger alkali is used, but plain old baking soda works well and is, of course, readily available.

    1. Yum….pretzels. Now you’ve got me craving them. I haven’t noticed the baking soda making the pieces slimy. Or do you mean that the baking soda makes your fingers feel slimy? I do agree with that. Baking soda IS alkaline, baked long or not…well…once it touches water anyway. (You can’t have a high pH without water…it has to do with hydrogen ions and all that.) Hmm…I’ll have to pay closer attention. So far no trouble, though. I know it’s used in glass to a great effect. In fact, that’s an effect I would love to recreate in polymer..that crusty bubbly soda look.

  3. Thank you, Ginger! Great post! I use cornstarch all the time for beads. I’ve tried baking soda, but don’t like the graininess. The only complaint I have is that here in the Northeast, the cornstarch gets clumpy… I just make the areas where my beads will be smooth and rounded before I lay my beads in them.

    1. Clumps here, too. It’s often incredibly humid here. In fact, today’s the first moderate and clear day since the great Midwestern Monsoon began back in April. It’s down to a pleasant 48% humidity and I can finally do my spray experiment. Yay!

  4. I use baking soda for all of my beads. I also use leached clay so I don’t have problems with the baking soda scratching or marring the surface of the clay. Very interesting about the baking soda going slimy Claire. I haven’t had that happen to me yet. Mixing the baking soda and cornstarch together sounds like a good solution.

  5. Hi Ginger. I found that using corn starch with Kato was a bit of a disaster. It made the resulting baked piece more brittle. Cooking in the sodium bicarbonate didn’t seem to have the same affect. I should do a Ginger Experiment to compare and see if it is a consistent observation. I recall reading something by Sue Fisher, an Australian polymer artist, about this Kato/ Cornflour incompatibility! Thanks, as always, for great posts! Wendy

    1. I will have to keep this in mind, and I’ll pay closer attention. But I use Kato and cornstarch all the time and haven’t had a bit of trouble. Kato is very easy to underbake and end up with a brittle project because the baking time on the instructions is woefully insufficient. I wonder if that could be one of those “coincidence causing incorrect correlation” kind of things. Thanks for mentioning it, though. Stranger things have proven to be true, that’s for sure.

    2. Cara Jane Hayman

      Wendy I totally agree with you on the Kato/Cornflour thing. I don’t trust cornflour near my Kato – it does seem to make it more brittle and also I find it tends to stick and not come off unlike baking soda which doesn’t cause any problems. I have said this to a number of people who think I am crazy so I am glad I am not alone with this experience. Proper testing needed to clarify I think! Cara

        1. Perhaps it is the discrepancy in baking time to allow the heat to penetrate the cornstarch that causes the brittle results? Im not familiar with Kato clay and wasnt aware it was so sensitive to temp and baking time. I’ll have to keep that in mind if I ever decide to try it.

            1. It also sounds to me like it might be a problem of under-baked clay as opposed to leeching.
              Perhaps the insulation caused by the powder increases baking time, or even the temperature required, in an exponential manner specific to kato clay.

              To start with I would experiment with using one sheet cut into several equal pieces. I would then perform one test in which I bake for a set longer time, and another in which I use a modest temperature increase. With each test I would use 2 controls – one without a powder and one with an equal amount of baking soda to the cornflour (applied in the same manner). Dependent on results I would move on to incremental increases in baking time, and in temperature. Dependent on those results I might start increasing both temperature and time in the same test.

              This is my first post here. I love mixing science and crafts, and I really like the work and efforts made by you to perform controlled studies. Thank you for taking the time to do these things, and many thanks especially for the study in the translucency of different clays, it was fantastic and very useful for me.

              1. Yes, running a controlled experiment is really the only way to know for sure. The issue with doing any sort of strength tests, though, is evaluating the results. Without equipment, it’s hard to put a value on the “breakability”. If it’s really clear, like flexible vs instant snapping, it’s easy. But I’ve found that far more often the results are more subtle and along the lines of “Well, it sure seemed to be weaker.” I’ve been thinking for a while about how to evaluate strength in testing. Glad to have you on board, Grace. I love knowing another science/art person!

                1. Thank you for your welcome. I love it here, you have a wonderful website!

                  As for testing strength – there was an old technique, which I believe is still used in a much more advanced fashion, using a simple “see-saw” construction to drop a standard weight on the object to test impact and fracture strength.
                  A weight is suspended at a set height on one side of the see-saw. The other end is stopped from moving by a peg. The peg is pulled out and the weight drops at a set speed (thank you gravity!) to hit the object to be tested. I think such a structure could be built at home by someone handy with woodwork.
                  The results would have to be analyzed by eye, in lieu of expensive equipment, and considered by the tester which could lead to minor problems/errors, but I think such an experiment is perfectly acceptable for this purpose. The drop and impact could also be filmed on a smart-phone so the impact can be observed again if necessary.
                  I’m not sure how one could test tensile strength at home though, I’ll try to think of something.

                  I don’t know if you’ve already considered and dismissed this for reasons I’ve failed to consider. If you have, I hope this suggestion doesn’t come across as patronizing.
                  Best wishes,
                  Grace

                  1. Makes sense and there are lots of methods of strength testing. The big issue, though, is…what is strength? There are about 8 types of strength and they’re not in isolation. So, for instance, the flexibility of polymer clay come into play with testing tensile strength. Souffle is very flexible and very strong when you try to pull it apart or snap it in two. But is that stronger than Kato which will hold more weight but has less tensile strenght. How in the world to compare them all? See what I mean? I’ve tried a lot of methods and the bottom line is either way too many pieces used (it might take 30 strips of polymer before you find out the exact weight that will break a strip. Or it needs a way to measure (such as a force testing scale). I’ll keep thinking on it. I’m sure there’s a way. I need to pick Cara Jane Hayman’s brain, too. She’s a materials engineer and a polymer clayer and has done some admirable strength tests. But there’s just SO much to it. Thanks for weighing in. It’s all very good to think about. And I might pick your brain on this, too, when I’m ready to tackle it.

                2. Hi Ginger,
                  I’ve been having the same issue with the clay snapping. I do know that Kato needs to bake longer than manufacturers suggestion, I’ve increased the time, but I can’t seem to find that sweet spot between cured and color change on White Kato. The pieces that get past the snap point turn out taupey in color. I’ve even added a layer of foil to help shade the cornstarch covered pieces. Keeping free form items White and fully cured seems to be my issue. Anyone having success with Kato White?

    3. Bertha Adamson

      Sorry I didn’t find this earlier to share this info. I have had the privilege of taking a few classes with Donna Kato and 1 – she uses/recommends baking soda (she had the big 5lb bag you can get from a certain big box membership store) and 2 – regularly bakes longer and even hotter than the package instructions. So under-baking is definitely a risk with kato clay.

  6. Hi, Ginger and friends,
    This may be a bit long, but I will try to “Reader’s Digest” it.

    I have done ALL of my baking in baking soda for over two years, since I read some posts about people burning their pieces, and I had one Premo copper piece bubble and not *quite* scorch on the back from sitting on the countertop convection oven tray. After doing some research online of how to prevent the scorching, I found BIG boxes of baking soda, I think they were 3 or 4 pounds, and bought 3 of them, because I wasn’t sure how much soda it would take to bury my pieces to protect them. I also bought a set of 3 cheap aluminum baking trays at the Dollar Store. My countertop convection oven is small, so an 8 inch square tray fits nicely, leaving room for my oven thermometer. Also, the 8 inch tray fits nicely into the flat metal sheet tray that came with the oven, which gives me a more solid thing to pick up. At that time, I was wrapping the top of my cheap aluminum baking tray with aluminum foil to keep the soda from being blown around in the convection oven.

    Then I wanted to bake a votive glass with clay on it, and needed a taller baking tray. Lightbulb moment! Remember, the baking trays came as a set of three. I made a cardboard collar inside the tray from an old file folder box, to make it taller. By serendipity I made it just short enough that I can turn a second baking tray upside down as a lid. I was able to stand the votive holder in the tray, partly fill it with baking soda and then drop a round bead or two into the baking soda, saving space outside of the votive for bigger pieces.

    It sometimes takes me two or three days to make enough pieces to fill the baking tray up. I don’t like running the oven for only a few pieces. So I put them on parchment paper on top of heavy cardstock (cereal boxes) pieces cut to be just a bit bigger than the piece. Then when I think I have enough pieces to fill the tray (or I’ve made something that I just can’t wait to see baked!), I start filling the tray.

    I have a ceramic tile in the bottom of the tray for support. Then a thin layer of baking soda, maybe 1/4 inch, covering the tile. Then a layer of cereal box cut to fill the tray. This gives me a flat area to put bigger cabochons, etc. on. I lay them out so that they fill the tray but have plenty of space between them. Then I use a wire sieve and sieve the baking soda over the pieces so that they are all covered by at least half an inch of baking soda. Then I start putting in other pieces on top of the layer. Flat-baked pieces go in on their cardboard and parchment paper sandwich. Round or irregular pieces get a mound of baking soda each, and I drop them in gently, so that they settle into it. Sieve more baking soda over everything, adding pieces where I have room. I use a soft paint brush to move the baking soda around GENTLY if I need to. I fill the collar almost to the top. I ALWAYS wear a dust mask doing this, because the baking soda can put a lot of dust into the air. Turn the second tray upside down and slide it down over the collar until the flat edge rests on the flat edge of the bottom tray. Pick up the whole unit (probably weighs 2 or 3 pounds with all of the clay and baking soda in it), slide it into the cold oven, shut the door and turn the oven on. Once the thermometer shows that the oven is up to heat, turn the timer back to an hour. When the oven turns off, I leave the whole unit in the oven until it is cold. Then I use a plastic rice ladle (fairly flat and thin) to scoop the baking soda out, sieving it back into a 4 liter ice cream bucket with a lid for next time. As I find the baked pieces, I transfer them into a plastic colander, which I use to wash them off in – after I lost a small piece down the drain, trying to wash them in my hands ;( The cardboard and parchment paper pieces go into a storage drawer for the next round. If I need to rub one gently under the running water, I always hold it over the colander. I have noticed a slightly slimy feel as the baking soda starts to wash away, but it goes quickly.

    I am using the same baking soda that I started with and there is no change in colour or consistency. This may have something to do with my sieving it in and out, I don’t know. I just started doing this because I was concerned about missing some small pieces.

    If I want to do an embossed piece with liquid clay on it, I put another piece of parchment paper over the top. I don’t know if the baking soda would stick to the liquid clay, but I don’t want to take any chances.

    * I have never (touch wood) scorched a piece since I started doing this.
    * I have not had a piece distort, once I figured out about using the cardboard pieces as support for flat backs.
    * I use a lot of Premo Translucent and White Translucent in my pieces and I have not had a piece darken at all since I started doing this.
    * And I can bake an incredible number of beads, cabochons, and bigger pieces in one go in that little 8 inch square tray because of being able to layer them.

    I also find that with the passive mass of the baking soda, I usually get very little fluctuation in temperature once the oven is up to heat. I never leave my studio while it is on, in case, but I am able to get one with other things, checking the oven thermometer every few minutes. Before I found this method, the temperature looked like an ECG and I had to sit there and adjust it every couple of minutes.

    I hope that this long post helps someone with some baking problems.

    1. It wouldn’t increase the temperature. It would work for cushioning and protecting the clay during baking, except that it would be coarse enough to leave a visible texture in the surface of the clay. If you had sand that’s fine enough to be usable for this purpose, it might be a health hazard (eg. silicosis of the lungs). Sand would have to be brushed off the baked pieces and seems like it would be more work than rinsing in a sink. Cornstarch just seems simpler.

    1. The raw clay will get shiny spots where it sticks to the foil, and any wrinkles in the foil will transfer to the clay, too. So that becomes an issue. Adding cornstarch to the top would insulate it further, of course. You don’t need to do quite that much insulation. Too much insulation keeps the heat from reaching the clay, leading to underbaking. You just want to shield it from the heat, so just one or the other is just fine. But use the foil as a tent, not as a “jacket”, if that makes sense. It shouldn’t touch the clay.

  7. I used cornstarch in shaping the FIMO petals for my flutes – instructions said to do so, but then had some leftover petals that I squished back into a ball and put back into the bag with the other clay. Can cornstarch be mixed in with the clay and then the clay used as regular clay?

    If it could be, this would also make using cutters on clay a whole lot easier. No more sticking in tiny corners. 1st smear the clay with cornstarch.

    Nervous about baking the flutes, I kept them on their tile plates, covered with cornstarch. Unlike the instructions, I didn’t turn them upside down. The flower petals would not have turned out right. I stood them on their base, which was concaved. After baking, most of the cornstarch brushed off, or rinsed off, but on two some of the cornstarch was stuck to the underneath of the base, in the center, as if it had baked on. I had to use a knife and scrape to get it off. There was no clay or water under those glasses, nothing but glass and cornstarch. Maybe a trace of clay on the underneath rim, a minute trace. I’m baffled over why the baked on cornstarch. I probably didn’t need to use it. I was nervous about glass on tile with no insulation between them.

    1. Yes, the remaining cornstarch can be mixed back into the clay. Just keep in mind it might make the clay stiffer and possibly a bit weaker, depending on how much there is. How did the flutes turn out? I was wondering.

      1. They were beautiful, stunning! The wedding coordinator, my daughter, the florist, everyone loved them and was in awe that I handmade them. I asked the coordinator if she thought they looked professional and she adamantly said yes. She showed them off to others. Sadly, I was so tired, I must of left the lens cap on when I took the pics. I have to make another for a 2nd Maid-of-Honor & will get pics of it, plus the Photographer took pics of them, so might get pics back. Tell you what, making peonies on flutes was hard, and mixing FIMO was too. I have color codes now for blush and ivory tho 🙂 I learned a whole lot in the process. Using the cornstarch on cutting was one.

        1. Wow, congratulations! I know you worried about them so much. I do want to see a pic, so when you get one let me see, okay? Well done you!!!

  8. Great info, Ginger! I’ve used cornstarch, but not baking soda yet. Hmm Something new to try, I like it! 🙂 For Ginger and Ann Dillon re clumps, have you tried storing the cornstarch (salt, sugar or any other loose or powdery dry good) with a saltine cracker in the storage container? I live in Oklahoma where humidity is a monster and I keep a cracker in those things year round, well, in salt/sugar shaker/bowls. I haven’t had much issue with cornstarch, but that’s a thought to try. I don’t know why it wouldn’t work in cornstarch, flour, etc. too. The cracker trick is one I learned from a boss in a restaurant 30 years ago. It absorbs the moisture (natural humidity or steam from a stove) in the containers and keeps my dry goods loose and non-clumpy. You can use the same cracker for months, until it starts to break/crumble. I replace mine about every six months. 🙂

    1. I’ve heard of the cracker trick. We all have rice in our salt shakers for the same reason. I need to do something similar for my garlic powder….that stuff gums right up. Thanks for the tip, I’m sure it’s new to a lot of people.

  9. Hi there, Great website! I can’t get enough of it!

    Anyway, I’m new to polymer clay and I’ve just created some little pendants with pearl ex shimmer dust on them. Do you recommend baking them in baking soda then? Or will the water take off the shimmer when you wash them?

    1. Hi Clare, that’s very kind of you to say!

      No, there’s no need to bake in baking soda. You’d only really need to do that if you’re worried about browning or the item falling flat and needing support during baking. Browning isn’t a concern if you’re using pearl ex, really. The pearl ex will actually stick quite well and won’t wash off, but avoiding it is even better.

  10. Hi Ginger. I am a newbie at making polymer clay and right now, I am so overwhelmed, i don’t know where to start. Here is a list of my questions.
    – I use a glass tile, which I have wiped clean, to roll my polymer clay. However, the clay sticks to the surface of the glass when I try to lift it. Will using baking soda help? If I do, will it affect the look or feel of the finished product since I may have to adjust my design as I work along, meaning the baking soda may mix with the clay itself?
    – when working on a flat piece, how do I make pieces of even thickness ( thicker than the pasta machine can make )? What is the maximum standard thickness when making polymer clay?
    – what happens when I over-condition my clay?

    1. Polymer clay sticks to smooth surfaces such as glass. Don’t use cornstarch or baking soda…this isn’t a pie crust! It’s very easy to lift from the tile, however, just slide a long blade underneath and release it from the tile. A lot of us will roll out the clay onto a piece of paper instead of the tile when it’s important that it not stick.

      If you need a piece of clay thicker than the pasta machine can make, just stack multiple sheets, making sure to avoid bubbles. Use a roller to make them adhere well.

      There is “maximum standard thickness”, but you might find that pieces thicker than 1/2 or so will take long times to cure. You might want to bake in stages in this case.

      You can’t really over-condition clay. It might get too warm from your hands and get sticky. In that case, just let it sit a while and start again.

  11. How do you remove the types of flour that get gummy when wet? I only have that type around and use it during molding to prevent dirt and fingerprints.

    1. Just keep washing, I suppose. Just rinse the piece under running water. Use an old toothbrush if necessary. Cornstarch (corn flour) really is worth it, though, and readily available at any grocery. It’s the stuff you use to thicken a clear sauce.

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