How to Bake Polymer Clay: Part 3 – Tips and Tricks

Polymer clay, also called polyclay or fimo, is a modeling material that you can cure or bake at home in your regular oven. Today I’m finishing my series on How to Bake Polymer Clay, with a focus on Tips and Tricks for getting the best results when curing your projects. Check out the other articles, too. Part 1 was on Choosing your Oven and Part 2 was about Temperature.

How I Bake my Polymer Clay Projects

Just as each cook has his preferred way of making scrambled eggs, each polymer clay artist has a preferred way of baking their clay projects. I’ll describe my method and show how I bake my jewelry and bead projects. This isn’t the only right way to do this, but I have had really good results. I’ll talk about my process and then I’ll go into more detail about different philosophies, strategies, and tips.

I use my home oven because it gives me more uniform and reliable results than when I’ve tried using a toaster oven in the past.  I almost always bake my polymer clay projects covered, using two aluminum foil pans, one inverted as a lid, and I clip the whole thing shut with a binder clip. Inside the pan, I place a ceramic tile, then a piece of scrap copy paper, and on top of that, my project.

Polymer clay in baking pans

I do use an oven thermometer to verify that my oven is baking at the correct temperature. I bake Fimo, Souffle, Premo and Cernit at 275° (135°C), Kato Polyclay at 300°F (150°C), and depending on the project Pardo at 275-325°F (135-163°C).

I preheat my oven, making sure that it’s fully heated to the correct temperature. Then I place my foil pans in the oven, shut the door, and start the timer. I used to rely on the oven’s timer but I’d forget and go outside where I couldn’t hear it so I now use a portable timer that I just clip to my shirt or carry with me. (Your smartphone likely has a timer app that would work as well.) I sort of guess how long to bake my pieces…I don’t measure with a ruler or anything like that, but I do always bake longer than what I think I “should”. For most things this means about 45 minutes for a 1/4″ thick piece.

Use a standard binder clip to hold foil pans shut when baking polymer clay. The Blue Bottle Tree.

When the timer goes off, I take the foil pans out of the oven, remove the clip, and check things out. Most of the time I’m happy. I usually am too impatient to let things cool off on their own, so I often will pick up the copy paper and set it on the countertop to cool (as the ceramic tile holds heat a long time).

This is the most common way that I bake, for most of the work I do. But there are lots of times when I vary from this. I’ll discuss this and more below. Read on!

How Long Should I Bake Polymer Clay?

It’s no wonder that people are confused about this one. Here’s what various packages of polymer clay tell you about baking duration:

  • Fimo: 30 minutes
  • Pardo Art Clay: Minimum of 30 minutes
  • Cernit: Approximately 30 minutes
  • Kato Polyclay: 10 minutes
  • Premo: 30 minutes per 1/4″ (6mm) of thickness
  • Sculpey: 15 minutes per 1/4″ (6mm) of thickness

Most polymer clay artists will agree that these are the absolute minimum times that you should use, and the recommended 10 minutes for Kato is just plain erroneous. Polymer clay becomes much stronger when it is baked longer than these minimum times. You cannot burn or damage polymer clay by baking it for a very long time, even hours. Unlike food, which will burn if left too long in the oven (because the moisture is driven out), polymer clay will not burn if baked at the correct temperature. The limiting factor, though, is that light colors of polymer clay will darken and brown with longer times in the oven. It does not damage them, but it will easily ruin your effect, especially if you’re working with light or translucent polymer clay.

I always recommend baking at least 45 minutes per 1/4″ of thickness and even longer for thicker pieces. For optimal results, do what works for you, not what a package says.

Not sure you’ve baked your piece long enough? Read about how you can tell if your polymer clay is baked enough in Part 4 – How Long to Bake Polymer Clay.

Position in the Oven

When you put your polymer clay in the oven, try to center it as far from any heating element as possible. You want good air circulation around your items, so that the heat can distribute evenly inside the oven. Put it on the center rack, equidistant from the elements, and keep it away from the oven’s walls. This is obviously more difficult in a toaster oven as the baking chamber is so small. But if parts of your project are too close to the heating element, it will burn.

Protecting your work from the heat

As anyone who has ever held their hand above a stove’s heating element can attest, it gets awfully toasty! Even if the overall temperature in the oven stays where you set it, every time that heating element cycles on, it glows red hot and can singe your polymer clay pieces if they’re too close. Some ovens don’t regulate this very well and the element will scorch things, quite badly at times. The best way to protect your beautiful artwork from baking disasters is to protect it and shield it from the heat by keeping it covered up.

Aluminum foil pans protect polymer clay from the heat during baking. The Blue Bottle Tree.

I use an aluminum foil cake pan, most often the 8″ x 8″ size because my 6″ ceramic tiles fit perfectly in the bottom. (Those of you outside the US will need to find the sizes that work for the materials you have where you are. In the UK, I know you can get 150mm tiles and 240mm square pans.) For larger projects I use larger pans and tiles. You could use a sheet of aluminum foil. Or a covered roasting pan. Or an upside down pan. Covering your work protects it from the heating element and it also helps keep the heat contained at a steady level inside the pan, leading to a more complete and reliable cure.

Another fantastic bonus of using a cover is that the chemical smells that come from baking polymer clay will be greatly contained. The few times that I have baked uncovered, my husband has come to me, worried, because he could smell the clay and thought it was burning! (It wasn’t.)

One other nice bonus that comes from using the foil pans is that I have a cover for my unbaked pieces in the studio. Sometimes I’ll have the pan sitting there for days until I’ve made enough pieces to bake. The cover keeps the dust and curious kitties from ruining my clay.

If you use a toaster oven and have a tiny space, you could use the tiny aluminum foil pie pans the same way that I use the larger pans.  Any pan with a lid that  is oven safe could be used to protect your clay while baking. Keep your eye open for a small unpainted metal box, or even a tin. Run it through the oven by itself first to make sure it will handle the heat, though, just to make sure.

Maintaining a Constant Temperature

Convection ovens are much better at keeping a consistent temperature, but conventional and toaster ovens use a hot element, cycling on and off, to keep the space heated. The element can burn your clay, as I’ve already stated, but there’s also the problem that curing of your items can be inhibited if the temperature doesn’t stay high the whole time. If your oven is one of those that gets fairly cold before the element kicks back on, it might be helpful to place ceramic tiles on the rack in the middle of the oven. This will act as what’s called a “heat sink” to help hold and evenly distribute the heat. You could also use an old pizza stone if your oven is large enough.

This is why I use a ceramic tile in the bottom of my foil pan baking system. It helps keep the temperature constant. I also use my ceramic tiles as work surfaces, if this is a new idea for you, you might want to read about how ceramic tiles are one of my most indispensable tools.

Support and Protective Material

When you place raw clay on a glazed ceramic tile and then bake it, the places where the clay touched the tile will be shiny. To prevent this, merely place your item on a piece of scrap copy paper, an index card, or a piece of card stock. Don’t worry, the paper will not burn. But make sure that it doesn’t have any printing or writing on it as the inks could transfer to your clay.

If you’re baking round beads, setting them on a flat surface is a recipe in frustration! To keep them from rolling all over the place, merely accordion fold a piece of blank copy paper and set your beads in the folds. They’ll stay in one place and they won’t have shiny spots.

baking polymer clay beads

Another method is to use a piece of polyester quilt batting. Again, it won’t burn in the oven, and it keeps your pieces from getting a shiny spot. Batting is a great tool, too, if you work with sculpture and need to support parts of your piece during baking. Just use lots of polyester fiberfill to prop it all up.

One thing to note about using paper, though. Don’t leave your art piece on the paper for very long before you bake it. You might notice an oily spot on the paper…that’s the liquid plasticizer that’s leached out of your clay. A small amount won’t hurt your clay (make sure to discard the paper afterward, though). But if excessive amounts of plasticizer are leached out, it might weaken your piece.

How to prevent browning of your clay projects

Translucent and light colors of polymer clay are very susceptible to turning brown during baking. This is not an indication of burning and is not dangerous, but it is frustrating. It’s just one of those thing you have to work around and there are some things you can do to prevent, or at least minimize the problem. Before we get to those, though, make sure that you are baking at the right temperature and are covering your pieces during baking to prevent the heating element from damaging your work. Here are a few other things you can try.

Bury your Beads

Another strategy to protect your polymer clay from the heat of the oven is to bury them in baking soda (bicarbonate of soda) during baking. Other people use cornstarch or salt. To do this, just pour an oven-safe bowl of your favorite powder, dig a hole, and put your beads inside. Put the whole thing in the oven to bake. After baking, you will need to rinse the powder off the beads. Some people report that cornstarch is harder to rinse off and leaves a white residue, so you might prefer to use baking soda if that’s the case. Regardless, don’t leave the beads sitting around unbaked in the powder for very long, though, for the same reason as with the paper above. The plasticizer can possibly leach out of the beads, leaving them brittle.

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

Experiment with Time and Temperature

Higher temperatures and longer bake times lead to more browning. So reducing the temperature or the duration of baking can solve the problem of browning. But, as I’ve discussed previously, that can also lead to weakened and underbaked projects. I suggest carefully experimenting with minimizing the baking time and temperature while at the same time monitoring the project’s strength. You need to bake long and hot enough to be fully cured and strong. Try the other strategies first, and if you still have unacceptable browning, then try experimenting with the time and temperature of baking.

Preventing Plaques and Cracks

Plaques are whitish areas that appear in the middle of a piece of polymer clay after curing. They look like they’re air bubbles but seem to happen when there was no obvious air trapped in the raw clay before baking. Fimo and Pardo are notorious for this problem and it’s more obvious in translucent and light colored clay. It’s been suggested that they are caused by water vapor or air collecting in the clay during curing and that they are caused by or exacerbated by sharp contrasts in temperature during baking or cooling.

Sometimes cracks appear in a clay piece immediately after baking, apparently caused by expansion of the clay mass during baking. Sudden temperature change also seems to be the culprit for this problem.

A commonly suggested solution for both plaques and cracks are to cure the clay without creating thermal shock. To do this, place your covered clay into a cool oven, turn it on to the correct temperature, and then begin timing once the proper temperature has been reached. After baking, turn off the oven and leave your items inside the oven until they have cooled thoroughly.

Can you bake polymer clay more than once?

A common question for those new to polymer clay is “Can you bake polymer clay more than once?” The answer is YES! There is no reason you can’t bake a piece of clay as many times as you need to. In fact, for complex pieces it’s common to bake parts of the piece separately and then assemble and attach them after baking. It’s also perfectly fine to attach raw clay to baked clay and bake that. Sometimes it’s the only way you can get certain effects.

High Altitude Baking of Polymer Clay

If you live at a high altitude, then you already know that the laws of physics can do some strange things to your baking times and temperatures. You might very well need to make adjustments to your polymer clay baking times as well. I don’t have personal experience with this, but I’ve read that mountain dwellers have success by raising the baking temperature about 25°F (or maybe 10°C) and baking for 15 minutes longer. Your experience might be different depending on your altitude. But if you’re doing everything right and still getting underbaked clay, this is something to be aware of.

Alternate Methods of Curing

Microwave

Do not use a microwave to cure polymer clay. It’s the wrong kind of heating process. It’s not going to cause sparks or anything like that, but it will cause smoke when it burns! Read more about if you can bake polymer clay in the microwave in my article about it here.

Boiling

For some reason there is a controversy about using boiling water to cure polymer clay. Some people say that it works, but that just isn’t realistic. Water boils at 212°F (100°C), which is a temperature too low to cure polymer clay. You’d think that adding more heat would raise the temperature of the water, but in reality it doesn’t. Blame physics. Now some people will say that boiling for a long time does give a complete cure for polymer clay. I am very, very skeptical of this.

However, I can conceive of why you might want to boil a polymer clay sculpture, for instance, to allow the water to support the item long enough to partially cure. This might be helpful with complex thin projections or pieces that would ordinarily be too floppy to bake without the support of the water. You would then fully bake the item at a proper temperature in the oven. But that’s not something most of us are going to be dealing with.

Heat Gun

A heat gun is a valuable tool for working with polymer clay. You can spot cure polymer clay with a heat gun but you have to be very, very careful to keep the gun moving at all times and not get too close to the clay. Heat guns produce enough heat to scorch and burn polymer clay causing it to blister and turn black (and produce irritating fumes). Yes, I hang my head in shame here. I have done this. But as long as you’re super careful to avoid burning, you can sort of “soft cure” clay to get it to solidify. You might use this technique if using liquid clay to assemble a sculpture, for instance. But it’s not a complete cure and you would still need to fully cure your project in the oven.

Cynthia Tinapple does use a heat gun to cure her polymer in place in the wooden bowls she creates with her husband Blair Davis. But she also uses a digital thermometer to make sure the clay is actually reaching curing temperature. For most of us, this isn’t a generally reliable way of curing polymer clay.

Well that’s all I can think of. You should have a pretty good idea of how to bake polymer clay. Now go make something beautiful!

This article was Part 3 of a series on Baking Polymer Clay. Part 1 was about Choosing the Right Oven and Part 2 was about Using the Right Temperature. Next is Part 4, How Long to Bake Polymer Clay. I hope you found this series to be useful. If so, why not sign up to get an email notification the next time I post. I’ve got lots more great articles planned. Thanks!

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