Air Bubbles – Hot air expands, so air trapped within a piece will cause a bulge that often cracks or breaks. Thick Pieces – If you're making something that is thicker than ½ inch (13 mm) or so, you'll likely see cracks on the surface. Instead, bake in layers or with a compressed foil core.
Do not put the clay into an already hot oven as it is likely to crack. Baking time depends on the size and thickness of your sculpture. For a small 5in sculpture, about 15 mins will generally do, while a larger one will need repeated bakings.
Cover the clay with a tented piece of aluminum foil or cover it with an upside-down baking pan. Bake using a conventional home oven or a toaster oven and adhere to the time and temperature listed. In most cases, you can bake polymer clay at 275 degrees F for 15 to 30 minutes per ¼ inch of clay thickness.
To have the best chance of blending the baked and unbaked clays together and look seamless, I've found that the best thing to do is to only add a tiny bit of clay to the area needing fixing. If it's a crack, take a tiny piece of clay and roll it into a thin snake, placing it over the crack.
Clay has a memory. So in an effort to erase the memory of a crack, score the area in question deeper and larger than the crack itself (2), then place a bit of scored soft clay into the space you've made and compress it with a rib (3, 4). This will heal a crack in most cases, depending on how dry the cracked clay is.
Polyform Polymer Clay
Polyform's polymer clay is the original oven-bake clay. Available in a 1.75 pound pack, this white Sculpey clay is super soft and pliable and won't dry out even when exposed to air for extended periods of time.
When you bake polymer clay on a baking sheet, the bottom changes during the curing process and becomes shiny. If you want to avoid this, be sure to line your baking sheets with parchment paper. This can ensure the bottoms of your creations keep the same sheen from top to bottom.
Dunting is a special type of crack which occurs from stresses caused during firing and cooling. These stresses primarily occur during two critical points of firing called silica inversions which occur at 1063 degrees F (573 degrees C), and 439 degrees F (226 degrees C).
Between 480–700ºC chemical water (“water smoke”) is driven off. Upon cooling, cristobalite, a crystalline form of silica found in all clay bodies, shrinks suddenly at 220ºC. Fast cooling at this temperature causes ware to crack.
Overbaking will cause darkening of the clay, and burning can cause bubbling and darkening.
Add epoxy enamel resin to baked clay to provide a dimensional, glass-like finish to your piece. As it hardens, resin undergoes a chemical reaction and contracts slightly, creating a subtle dome-like effect advantageous to jewelry makers. From earrings to cabochons, a glassy domed coating makes wearable art pop.
You may use it for baking your project, shaping your structure, or covering your clay before placing it in the oven. So, yes, it is entirely safe to bake clay with tin foil in it. You can use tin foil as the core for polymer clay figures or any other project that has a bit of depth.
If you take your clay out of the oven and find it's still soft, it could be one of two reasons: the temperature was too low, or it wasn't baked long enough.
To test the curing, try pressing the tip of your fingernail into the bottom of your piece after it has cooled; it will leave a mark but will not actually enter the clay. For Premo! Sculpey, preheat to 275 degrees F (135 C).
To bake the clay, heat to temperatures around 100℃ / 212℉ and at 20 to 30 minutes depending on the oven being used. A typical toaster oven with a small sculpture may require less time, though the thicker the clay, the longer it may take to bake.
Air-Dry Clay, also called ADC, is a modeling clay, that as its name suggests, is a modeling clay that air-dries. No heating, no oven – just leave the modeling clay at room temperature and it will begin to harden. Don't worry, the modeling clay won't harden while you're working with it.
Original Sculpey®: This clay is perfect for beginners. Original Sculpey® is soft and easy to mold until you bake it in the oven. Plus, it's affordable and available in bulk sizes for school projects and simple crafts.
Sago Brothers modeling clay is very soft and smooth, no odor, doesn't crack, fade, or lose shape.
Using clay that is too soft. Making your own clay and not mixing it well enough. Not wedging well enough. Making large pieces, especially flat ones having a big diameter.
Baking air dry clay can cause it to warp or crack. It is best to avoid this method altogether if you can. If you need to speed up the drying process, try putting the clay in a dehydrator or desiccant chamber. These methods will help absorb the clay's moisture and speed up the drying process without damaging the clay.
In a bowl, mix a ratio of 80% PVA glue to 20% water to create a creamy consistency, and then coat your fully dried clay piece, and allow the sealer mixture to dry. Once you have applied your PVA glue mixture or acrylic medium, you can then apply 3 coats of acrylic paint to seal your work.
You can bake polymer clay multiple times. It can be handy to bake your clay in stages to avoid causing any damage to what you've done previously. Although it is important to note that it will be difficult to attach raw clay to a piece that has already been cured.