So you’ve made your polymer clay figures, beads, or charms and you’ve read the instructions for baking. You set your oven’s temperature and preheat the oven. You calculate how long to bake polymer clay. And you set the timer and wait. But…how can you tell if polymer clay is baked enough?
I asked my husband this question, and the cheeky sod answered back, “You know polymer clay is fully baked when the timer goes beep, beep, beep.”
Yeah, well. That’s not the answer. But seriously, how can you tell?
It’s really common for new clayers to notice how flexible their baked polymer clay is and assume that it’s not fully cured. But actually, that has nothing to do with it. All baked polymer clay is flexible to a degree after baking, and some brands are downright bendy if they’re thin enough. (It’s not so noticeable if a piece is very thick.) This is because polymer clay is actually vinyl and just like an old vinyl record, it’s flexible. (How flexible SHOULD it be? And should it always be flexible? What if you can’t bend your clay? Read more here.)
Polymer clay is a moldable plastigel made of PVC particles suspended in a mixture of plasticizers, fillers, stabilizers, lubricants, and colorants. It becomes less viscous (runny) as the temperature increases. That’s why body heat and summer temperatures can make polymer clay too soft. But once the temperature increases to a certain point, the vinyl particles in the clay begin to fuse together and the clay mass begins to harden. The clay must stay at the right temperature long enough for the particles to fully fuse, making a strong final result. If you don’t bake your clay long enough, the fusion will not be complete and the clay will easily break and crumble.
How Long to Bake Polymer Clay?
But how long is long enough? Underbaked polymer clay looks just like fully baked polymer clay. You can’t really tell by feel if the fusion process is complete. The only way to tell is to actually attempt to break a piece. Fully baked polymer clay will bend before it breaks.*** Underbaked polymer clay will snap in two or crumble when you try to break a piece in your hands. Now obviously that’s not the best way to check because you run the risk of breaking your clay creation. Not a good strategy!
***(Note: Sculpey Original and Sculpey III are both brittle and will often break easily with your hands, even when fully baked. I nearly always recommend using stronger clay brands such as Premo, Souffle, Fimo, Kato, Cernit, Pardo, and PVClay when you need a strong, durable clay or if you’re having breakage issues.)
Know Your Oven
The best strategy is to know how your oven works and know how the clay behaves in it for various temperatures, times, and thicknesses of clay. First off, make sure you have a good baking setup including an adjustable oven, baking pans, and a separate oven thermometer. Experiment with your oven to see what setting needs to be used to get the temperature that your clay requires for curing, this could be from 230°F (110°C) to 300°F (149°C). Watch the thermometer through the door and see what happens to the temperature throughout the baking cycle. Be aware that the temperature dial on most ovens is wildly inaccurate. Adjust your oven accordingly to get the desired temperature.
Then do some tests. Make bits of clay in various thicknesses and bake them for varying amounts of time. Keep track of it on paper (you won’t remember…trust me). And then once they’ve cooled try breaking the pieces. You’ll see right away what baking times work best for varying thicknesses of clay. You’ll also notice that the strength of clay keeps going up with bake time, too, and baking a really long time will give you much stronger clay. This is a good thing to know when you need extreme strength for a specific project.
Many people with dedicated claying ovens just adjust it to bake at one temperature and they never touch the dial after that. Others have marked where the “Fimo, Premo, and Kato” settings are on their particular oven. The bottom line, though, is to know your own particular oven.
Bake Longer “Just in Case”
Of course, if you don’t want to mess with running tests, just bake “longer”. If you ask most polymer clay pros they’ll say they bake everything for an hour. Or longer. And for thicker and larger pieces they might bake for several hours. Longer baking will NOT burn your clay. Longer baking will also lead to stronger clay projects.
That being said, longer bake times can cause some colors of polymer clay to darken. White and translucent can turn slightly amber or brown. Red, yellow, and fuchsia can darken. This does not mean the clay is burned. To prevent, or at least reduce this tendency, make sure you always cover your polymer clay projects while baking. This can be as simple as a piece of aluminum foil over the top or as complicated as a set of dedicated roasting pans. Covering your clay will shield it from the oven’s heat and dramatically reduce color shifts that happen during baking.
So why do the package recommendations tell you to never bake longer? Keep in mind that manufacturers have to write instructions for ALL types of consumers. And most ovens are wildly inaccurate. So they have to give instructions that give a balance between adequate curing and the very real and frustrating reality that many ovens will be too hot and could cause the clay to burn. The instructions on the package are what is going to give adequate results for most consumers. They are not designed to give the optimal results for perfect and controlled conditions. Feel free to do your best to create the best possible baking conditions for your polymer clay so that you can get the best results possible.
Fixing Underbaked Polymer Clay Projects
What if you realize that you have some underbaked polymer clay. What then? Luckily, you can bake your polymer clay again, this time at the correct time and temperature. I’ve heard that this won’t give as strong of results as if it was baked long enough the first time. But go ahead and try. It might help. Also, polymer clay can be rebaked an indefinite number of times. You can even rebake it if you’ve already added paint or sealer, in most cases.
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