Have you ever noticed the words on the packaging that you shouldn’t bake polymer clay in the microwave? That’s very good advice. You shouldn’t do it! But why? Read on to find out.
Will Microwaves Heat Polymer Clay?
Microwaves are a form of energy sort of like radio waves and when they pass through food, the waves make the fat, sugar, and oil molecules in food vibrate and dance. And just like a Tuesday evening at a Zumba class, all that dancing creates heat. That heat is actually what cooks your food. Polymer clay doesn’t have much water and no sugar, but does have oil molecules. As microwave energy goes through the polymer clay mass, the molecules start to do their own version of a Zumba routine and begin to get hot. So when you bake polymer clay in the microwave, it heats up and starts to cook.
What Happens to Polymer Clay in the Microwave?
Because microwaves don’t heat evenly, parts of the mass will begin to cure and harden while others remain soft. Microwave ovens heat the inside of clay just as much as the outside, so as the cooking continues, parts of the mass will begin to superheat, melt, and actually bubble and boil while other parts of the polymer clay mass will merely begin to harden. After a few minutes, the overheated polymer will expand and ooze out. When that super-heated oozey stuff hits the air, it will begin to oxidize (burn), turn black and create smoke. When polymer clay burns, it releases acrid and smelly hydrogen chloride gas, which is nasty to breathe and harms lung tissue. At the same time, because this happens in mere minutes of beginning to bake polymer clay in the microwave, the outside of the clay mass has not yet had enough time for the plastic particles to fuse and create a solid baked polymer clay mass. This means that the clay is crumbly and weak on the outside and melted and horrible in the inside. In addition to the danger from burning, because the melted clay is super hot, you run the risk of burns if you squished a wad of microwaved polymer clay.
What About Softening Polymer Clay?
Can you use a microwave to soften polymer clay? Yes and no. Just like butter, silly putty, and chocolate chip cookie dough, polymer clay gets softer when it warms up. A microwave can be used to do the same thing, but please know there are limitations. You can’t just nuke a block for a couple of minutes or it will ignite like you see above. Sylvie Peraud suggests that you should make slices and then put them in for 10 seconds at a time. Any more than that and you run the risk of getting hot spots that will ignite. I generally recommend that you warm clay by putting a package in your pocket (or bra) or even sitting on it a while before you use it. Another way is to put the clay into a ziploc bag and immerse in hot tap water for about 10 minutes.
Can You Boil Polymer Clay in the Microwave?
Some people advocate using a microwave to boil water which contains the polymer clay. The problem with this is that it’s a simple fact of physics that boiling water never heats above 212°F (100°C), (give or take a few degrees based on elevation and water hardness.) Boiling water never comes close to the proper curing temperatures of most brands of polymer clay. While you may find that the item is hard after boiling, it will be incompletely cured and will be weak and easily broken. (This is true for stove-top curing as well.) Some brands of polymer clay will get an icky white residue when boiled as well.
The clay itself absorbs microwave energy and can still become superheated, even when submerged in water. I think there’s room for experimentation there, but it’s very difficult to control the amount of heat the items would be receiving. For a quality and reproducable cure, use a calibrated oven.
Combination Microwave/Convection Ovens
Can a combination microwave/convection oven be used to bake polymer clay? Yes, if you can turn off the microwave part and the oven functions like a regular convection oven, then that is fine and should give excellent results. For more information about properly baking polymer clay, have a look at my class on Baking Polymer Clay.
Does Sanding and Buffing Drive You Nuts?
I just published a comprehensive 120 page eBook on Sanding and Buffing Polymer Clay. It’s getting rave reviews and is absolutely packed with information you need to know to make sanding and buffing easier. Come check it out!