Getting Your Clay Ready
Before you begin any project, you must Condition it and possibly Leach your Polymer Clay. It doesn’t matter which brand you’re using or how soft it is out of the package. Conditioning is the process of softening the clay and literally moving the plastic particles around so that it is easier to work with, and more stable after baking. Leaching is sometimes necessary when there is too much plasticizer in the clay from the start. You may notice this in some of the softer clays. In this case you “Leach out” the excess plasticizer. Remember art class in high school when you had that terra cotta colored clay and you had to knead it and roll it until it softened? Well Conditioning Polymer Clay is much easier and not nearly as messy, believe me!
One tip that will help is to prepare the clay you’re conditioning by warming it up a bit. You can do this by placing it on a heating pad set to warm, put it in your lap, some people even sit on the block of clay to let their body heat do the warming. Whatever you decide, be careful not to cook it in the process of warming. For example, you probably don’t want to warm it up in the oven or even on top of the oven.
Conditioning
If you have a slicing blade carefully slice off a ¼ to ½ inch slice of clay. Use a smooth sided drinking glass or a pasta machine to flatten it out onto a smooth surface. When it is fairly flat roll it up into a snake, fold it in half and roll it out again. Continue to do this until there are no cracks when you fold the snake in half, then your clay will be completly conditioned.
Conditioning Clay the Easy Way
I’ve said it before and it bears repeating here, some of the greatest tools are found in the kitchen. Sometimes polymer clay can get really hard, crumbly hard. When it’s like this, polymer clay can be almost impossible, certainly frustrating, to condition.
When you have clay that’s been sitting around awhile (I have some that’s been on the shelf for years), using a mini chopper can be a real time (and hand) saver. You can find mini-choppers just about anywhere you can purchase full-size food processors. I recently bought a new one for $10.
Using the chopper is as simple as breaking up the clay, placing it in the chopper, about 1/2 a small block to start. Sometimes it helps to add some clay softener or mineral oil to help soften the clay. Turn on the chopper until the clay is forming little balls as in the picture below.
Polymer Clay after being conditioned in the food processor
Leaching Polymer Clay
As I mentioned above, some of the brands of polymer clay will be really soft or gooey (technical term), if you come across clay like this, you’ll probably know it. There are a few things to do when you have soft clay.
You can cool it off by putting it in the freezer; I find this better than the refrigerator because it doesn’t develop condensation while in the freezer.
Perhaps your hands are heating up the clay and making it softer, you can work on a marble surface, which will keep the clay cooler, or you can periodically dip your hands in ice water to keep them cool. I notice when the weather is really hot, even though I have AC, my clay is much softer and I usually do the freezer or leaching. I just can’t get excited about putting my hands in ice water!
Leaching is another option for firming up soft clay. One reason it is soft is that it may have too much plasticizer, or the clay hasn’t settled after manufacturing. Premo especially, can be left on the shelf for months in order to help it harden. Leaching clay will pull out the excess plasticizer.
First you must flatten your clay out using a smooth sided drinking glass or pasta machine, perhaps ½’ or more. Then you take two pieces of card stock, the heavy paper you can find in most office supply or craft stores. You can use notebook paper, but card stock will absorb more plasticizer. Then you place the sheet of clay between the two sheets of paper and roll over it with the smooth sided glass, or other roller. Let this sit for several hours. As it sits, you can see a dark spot on the paper where some of the plasticizer has begun to leach out of the clay onto the paper (see below). 
