As many, many people have found out, nail polish on polymer clay will very often turn sticky and goopy over time. It’s convenient, it’s simple, and seems like such a good idea. It’s very common to see polymer clay projects, especially on craft blogs, that recommend using nail polish as a glaze or gloss finish on polymer clay. Using Nail Polish as a Polymer Clay Glaze For more info on covering clay and preventing browning, see my class on Baking Polymer Clay. Then cover your pieces to prevent the oven’s element from toasting your polymer clay project. To prevent this, first make sure that your oven truly is baking at the correct temperature. Light colored or translucent polymer clay will commonly discolor and darken during baking. But when others follow this temperature advice, they end up with fragile, brittle, underbaked clay. What they think is 215☏ might actually be 275☏ in their oven. Will this work? Well, it might work for a specific person because they’re compensating for an incorrect oven. It’s common to read recommendations in forums to set your oven to, for instance, 215☏ (100☌) and bake for an hour or so. Many people assume that baking longer times at lower temperature settings will solve this problem. If you have burned polymer clay, you need to address your oven, not your baking times. If your project is close to the element, your thermometer could be reading the correct temperature but your project could still bubble and blacken. When the oven’s heating element cycles on and off, the heat radiating from it can be tremendous. (Fimo is a bit more sensitive.) If your project actually turns black and bubbles, then your oven is way too hot! As already state, ovens can be wildly inaccurate. Polymer clay does not burn unless it reaches temperatures near 350☏ (176☌). Want to learn more? Here’s my class on baking polymer clay that gives more info about choosing an oven, baking temperatures, and knowing if you’ve baked your clay long enough. Lighter colors may, however, discolor, so it is always better to do multiple bakings of thinner layers. If your oven is truly baking at the correct temperature, your clay will not burn. This means that a 1″ thick bead will need to be baked for two hours. Polymer clay should be baked for at least 30 minutes for each 1/4″ of thickness. I’ve been quite surprised to see that my oven’s dial is often off by 40☏ or more. I use two digital probe thermometers to verify exactly what temperature my oven is during baking. It’s therefore best to bake quite a bit longer than the label suggests to make up for this. (I like this inexpensive digital probe thermometer, but there are many others.) In the real world, even accurate ovens fluctuate during the baking cycle (and when you open the door). Most ovens are inaccurate and it’s important to use a separate oven thermometer to know what temperature your oven actually is. But you really do need to bake at a sufficient temperature for at least as long as the time stated on the package. The temperature on the package is a guideline, and you do have some leeway. To properly bake polymer clay, you must consider both time and temperature. Underbaked polymer clay can also have excess free plasticizer that can lead to cure inhibition in paints and glues, causing them to remain soft and/or sticky. Underbaked clay is not only less flexible, it is susceptible to breaking and crumbling. If polymer clay is underbaked, the fusion will not be complete and the resulting clay mass will be weak. Optimally, the particles will eventually fully fuse together and form a solid mass of plastic. As the temperature increases during curing, the powdered PVC softens in the plasticizer and the particles begin to absorb the plasticizer. Polymer clay is made from PVC powder, plasticizers, binders and fillers, lubricant, and pigments. Of course to have this kind of durability the clay must be properly baked, which leads us to the next point. The stronger brands of polymer clay are durable enough that you cannot break them with your hands, even when used as thin as 1/16″ (1.5 mm). Here’s more about choosing the best brand of polymer clay for your project. These weaker brands do have their uses, however, so save them for other projects. Sculpey III, Original Sculpey, Super Sculpey, and Bake Shop are all quite brittle after baking and should not be used, unsupported, in any area thinner than 1/4″ (6mm). For making things that are thin or have areas that are thinner than 1/4″ (6mm), make sure that you’re using a strong clay such as Premo, Fimo, Pardo, Kato, Cernit, or Souffle. Not all polymer clay brands are created equal and each has its uses and purposes. It’s even more horrifying to realize that you’ve sold something that is made from weak clay and won’t be durable. It is so sad to work hard creating something that breaks when it’s worn or used.
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