How to Bake Polymer Clay: Part 2 – Temperature

Learn about choosing the right polymer clay temperature for baking projects. Part of a series by The Blue Bottle Tree.Today I’m discussing baking temperature and why it’s so important for getting good results with your polymer clay projects. When baking polymer clay, temperature is everything! This article is second in a series on Baking Polymer Clay.  Part 1 of this series discussed choosing the right oven for baking or curing your polymer clay projects. Part 3 will be give specific tips and tricks about baking polymer clay.

For a good cure with polymer clay, temperature is important!

People often contact me for help when they’re having trouble getting good results with their polymer clay. And after some investigation, I almost always find that the problems are caused by baking polymer clay projects at an incorrect temperature.  One of the most important things you can do to ensure good results is to invest in an oven thermometer. They’re not expensive and can typically be found at most discount or kitchen stores for between $5 and $10. Every oven is different and many will operate at a temperature much different than you set. Some ovens are too hot and others are too cool. Even more take a long time to get up to the correct baking temperature, even once the oven’s “preheated” light has come on. It’s always best to check. Get to know your oven, watch what its pattern is. Does it get to temperature quickly? Does it hold the temperature or does it cycle wildly?  This is such an important factor that some professionals even recommend getting two thermometers just in case one of them is wrong!

Article about using the optimal temperature to bake polymer clay, without underbaking or burning your projects. By The Blue Bottle Tree.

Underbaking Polymer Clay

Underbaked polymer clay can be soft, crumbly, it might break easily. Underbaked translucent polymer clay isn’t as clear or translucent as it should be. And when you underbake a large item, even though it looks great at first, the liquid plasticizer in the uncured clay at the center will eventually cause the baked clay to degrade over time. It is extremely important to bake your polymer clay projects no lower than the recommended temperature for at least the correct length of time. In fact, baking your piece even longer (within reason!) will make your piece even stronger.

Sometimes people underbake their polymer clay because they fear burning or scorching their clay. Put your mind at ease. As stated on the Polyform website, both Sculpey and Premo do not break down and burn until the temperature reaches 350°F (177°C). The same is true for Kato Polyclay (as per personal communication with Tony Aquino, a chemist with Van Aken International.) Assuming your oven functions properly and you set the correct temperature, you are far more likely to underbake than burn your clay.

Overbaking Polymer Clay

Scorching and burning polymer clay does happen. And I’ve heard that it’s pretty nasty when it happens. Just think of what any burned plastic smells like! Burned polymer clay does release small amounts of irritating and caustic hydrogen chloride gas.  If you burn your clay, turn off the oven, open the windows, and leave the area until it clears out. Just like when you burn your pork roast. But aside from airing out the area and throwing away the burned mess, you won’t need to undertake any “toxic waste cleanup” or decontamination of the area. Though the room and your oven may smell bad for a while (no different from when you burn popcorn in the microwave…yuck!)

But you’re not going to burn your polymer clay unless you set the wrong temperature on your oven, your oven malfunctions, or your piece is too close to the element. It’s easy to accidentally set the wrong temperature, though. I’ve caught myself doing it several times for the simple reason that Premo bakes at 275°F but most of us bake a casserole at 375°F. So double-check and don’t let your “autopilot” take over!  Another thing that happens is there will be clay cooling in the oven when another person comes along and turns the oven on to preheat for making food. Next thing you know, your creations are up in smoke!

As I described earlier in this series, toaster ovens are notorious for having vast temperature fluctuations that can lead to “toasting” your polyclay projects. Many people opt to use a toaster oven out of fear that using their home oven is somehow dangerous. It’s my personal opinion that many toaster ovens are more likely to be dangerous because of these overbaking issues. I’ve read lots of sad stories of burned clay and I wonder how many of those cases would have been avoided if a full-sized oven were used. I think sometimes people try to avoid a possible or mythical problem but that then leads to a situation with a much higher likelihood of encountering problems. (Sorry, I know this is a controversial subject, but it’s my opinion, and I’ve heard it echoed by others as well!)

A lot of people are happy with their toaster ovens, but if you’re one of those who is getting burned clay projects, try using your home oven, with a separate oven thermometer, and see if you have better results.

Browning or Darkening of Polymer Clay

Even if your oven doesn’t burn clay, it can still cause discoloration much in the same way that bread turns brown when placed next to the heating element (toast!). Translucent and lighter colored clays are very susceptible to this. I’ll discuss some ways to prevent this and protect your artwork in part three of this series. But remember that reducing your oven’s temperature (as verified by a separate oven thermometer) is not the solution. You will just end up with underbaked, weak projects.

Learn how to prevent overbaked and darkened translucent polymer clay. The Blue Bottle Tree.
I was so upset when these gorgeous translucent mokume gane beads came out of the oven yellowed and darkened. This experience made me look for why this happened and find out how to prevent it in the future.

Times and Temperatures for the Best Results

Polymer clay manufacturers clearly state the recommended temperatures at which their products should be baked. Some brands warn you not to exceed certain temperature ranges. This is quite understandable and I have to officially side with the manufacturers who have chosen those temperatures for a reason. They are aiming for optimal safety and optimal results.

But it’s also common knowledge among professional polymer clay artists (who collectively bake a lot of clay) that the strongest results come when polymer clay is baked for much longer than the manufacturers recommend. I agree with this wholeheartedly. For example,  the instructions on packages of Kato Polyclay tell you to bake at 300­°F (150°C) for a mere 10 minutes. When I tried that, the clay was grossly underbaked and easily crumbled in my fingers. The same sized pieces of Kato Polyclay baked 30 minutes came out strong and impossible for me to break. Baking polymer clay for longer than recommended will not harm it in the same way baking a loaf of bread too long will give you a hard brown brick. Light colored clays might darken and discolor, but they will not burn. Even if you leave your clay in the oven all day long, as long as you don’t exceed the correct temperature, it will not burn.

Now contrary to my own advice and the advice of polymer clay manufacturers, I’ve often baked both Pardo Art Clay and Kato Polyclay at 325°F (163°C) without burning. Kato seems to be just a lot stronger at that temperature, but Pardo clay changes dramatically. It becomes both more clear and more plastic-looking and hard. I, personally, don’t mind that result, but the folks at Viva Decor (the maker of Pardo) probably consider it an unsatisfactory result and want you to keep the temperature lower. I’m not going to officially advocate baking polymer clay at higher temperatures, but I do think there is room for careful experimentation. If you choose to try this, be careful to use a separate thermometer and watch carefully for burning!

What Temperature Should I Bake Mixed Clays At?

Sometimes, especially if you’re making something from scrap clay, you will have a project that contains a blend of more than one brand of polymer clay. What temperature should that project be baked at? I’ve never seen an official answer from any polymer clay manufacturer, so I can only speak from my own experience. I always bake at the highest temperature needed of all the brands in the mix. So if I mix Kato Polyclay (which cures at 300­°F (150°C)) with Fimo (which cures at 230°F (110°C)), I will use the higher temperature. I’ve never had any trouble with this yet.

An exception would be if you are baking, for instance, the body of a cat figurine out of Kato and the ears out of Fimo. I’d bake the body at the higher temperature to assure a full cure and then apply the ears and do a second baking at the lower temperature.

The next article in this series, Part 3, is full of tips and tricks about baking polymer clay. I’ll show my baking setup and give lots of information about finding solutions to baking problems. Check back to get the next installment or check on my Facebook page for the link.  I’d like it if you’d join the mailing list, too. That way you’ll be sure to get an email when I make a new post.

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