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To my mind, modeling clay is one of the most fun media to "play" with. From faux beads to small figurines to plaques to Christmas ornaments to adornments for collages or scrapbook pages: every crafter can find an application for clay. Home cured clays which air dry or cure in the oven at low temperature are safe, easy and one of the most affordable crafts around.
With a few basic shapes (ball, cane, pear, teardrop) you can create almost anything. You can make clay molds; and then use the molds to recreate a design over and over. You can stamp impressions into clay; color it; texturize it; carve it. You can make it look like almost any hard substance from stone to marble to wood to bone.
I made an faux coral and jade bead necklace and earring set with Sculpey III modeling clay, using an antique Chinese "Prosperity" coin. The result, pictured on my site, looks quite authenic.
The choice of modeling clays and clay recipes is mind-boggling. It helps to understand the differences in order to decide which is suitable for your project.
I'll narrow the field to general use modeling clays and exclude the exotic types like rose petal clay, cinnamon applesauce clay and coffee clay! That leaves three general categories: polymer; cornstarch base; and bread base.
Polymer Modeling Clays
The leading polymer clays are Sculpey and Fimo. Pieces are cured in your home oven on low heat in just 15 minutes. Polymer clays have very long shelf life and are stored simply by wrapping in plastic and keeping in a cool, dark place. I've never had any harden in storage but if you do, there are diluents to make the clay workable again.
The choices of colors and finishes (such as stone, glitter, fluorescent and even glow in the dark) are wonderful.
The three main advantages of polymer modeling clays are: quick home curing; the consistency and range of color and texture; and the less than 2% shrinkage when cured.
Cornstarch Base Clays
There are many variations of cornstarch base clays. Some of the most popular are cold porcelain clay, Victorian salt clay, and "pasta francesa".
I like the porcelain designation because cornstarch clays are pure white and, if sealed after drying, they actually resemble fine porcelain. They require cooking to prepare.
Cornstarch clays containing salt tend to be more porous than the others. Cornstarch clays air dry; but drying can be accelerated in a warm oven. The shelf life varies from one week to one month depending on the ingredients, storage temperature and humidity. Expect up to 30% shrinkage.
Bread Base Clays
Bread base clays do not require cooking; they air dry; and will keep up to three weeks in the refrigerator. Shrinkage can be up to 50%. The "no cooking or baking required" aspect makes bread clays the perfect choice for projects to do with your kids.
As far as shrinkage goes, you can sometimes compensate by making your project x% larger than you want the finished product. Keep in mind that if you are making molds from which you will recreate a design over and over, the amount of shrinkage to expect almost doubles.
If you make a clay cast of a medallion that is 10mm in diameter, a cornstarch base impression could dry as small as 7mm and the medallions you make could be 4.9mm. If you use bread base clay, the mold could measure 5mm and your clay medallions may be as small as 2.5mm. That's a big difference!
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