We don’t know if you’ve ever noticed, but there are warnings on polymer clay packaging that you should not put it in the microwave oven. This warning is a very appropriate and correctly written warning, and we will try to explain why it should not be done.
Does the Microwave Heat Polymer Clay?
Can you bake polymer clay in the microwave? What happens when you do? Microwaves, like radio waves, are a form of energy and make water, sugar and fat molecules vibrate when they pass through food. This vibration causes molecules to rub or collide with each other. Heat is released during this collision. This heat is what actually heats or cooks your food. There are no water and sugar molecules in polymer clay, but there are oil molecules. As microwave energy passes through the polymer clay mass, the oil molecules begin to vibrate and heat up. And then…
What Happens to Polymer Clay in the Microwave Oven?
Since microwaves cannot heat every part of the polymer clay equally, some parts of the mass begin to cure and harden, while some parts remain soft. Microwave ovens heat the inside of the clay more than the outside. Therefore, as baking continues, some parts of the mass begin to overheat, melt, bubble and boil, while other parts of the polymer clay mass begin to harden. After a few minutes, the superheated polymer will expand and begin to form a liquid state. This overheated liquefied part will begin to oxidize (burn), turn black and emit smoke. When polymer clay burns, smelly hydrogen chloride gas is released, which is harmful to inhale and can damage lung tissue. In addition to the danger of hydrogen chloride gas from burnt clay, you also run the risk of burning your hand if you touch it because the molten clay is very hot and will not cool quickly.
How about softening polymer clay in the microwave?
Can you use a microwave to soften polymer clay? Both yes and no. Just like buttery chocolate chip cookie dough, polymer clay softens when heated. Likewise, a microwave can be used to soften, but please note that care must be taken. If you cannot set the appropriate time and keep it too long, it will melt and burn as described above. Our recommendation would be to slice the polymer clay mass and then microwave it for no more than 10 seconds at a time. You may run the risk of burning for more than 10 seconds. It’s good to be in control.
We generally recommend heating the clay by placing it in a ziplock plastic bag in your pocket, or alternatively, soaking it in hot tap water in a bag for about 10 minutes.
Boiling Polymer Clay in the Microwave Oven?
Some people claim to cook polymer clay by boiling it in a microwave oven in a bowl of water, but there is a problem with this. The boiling point of water is 100 °C and water cannot be heated above this level (100 °C may go up a few degrees depending on altitude and water hardness). This is a simple fact of physics. However, the curing temperatures of most polymer clay brands are above 110 °C. Although your clay may appear hardened after boiling, it will not be completely cured and therefore will be weak and brittle.
Clay itself absorbs microwave energy and can still overheat even if submerged in water. It is very difficult to control the amount of heat the clay receives in the microwave oven. For quality and reproducible curing, you should use a well-calibrated standard oven.
Both Microwave and Convection Ovens
Can a 2-in-1 (microwave/convection) oven be used to bake polymer clay? Yes, of course it can be used if you can turn off the microwave part and the oven works like a normal convection oven. For more information on firing polymer clay correctly, check out the posts on Polymer Clay Baking.