Conditioning clay is one of the more time consuming and least fun parts of working with polymer clay, but it has to be done.
Conditioning is the process of working polymer clay to prepare it for use. You do this by kneading the clay in your hands multiple times or running it through the pasta roller until the clay is easier to work with. Even if the clay you use (Sculpey III for instance) is already soft, it still needs to be conditioned in order to improve strength and longevity. A finished piece that wasn't conditioned well will damage/break easily.
Step 1: BoM
-Wax paper, acrylic sheet or tiles (a box of 4x4" plain glossy white tiles is about $10 at Home Depot)
Clay & Conditioning
-Liquid polymer clay
-Rolling tools ( piece of PVC pipe, pasta roller--$15 at craft stores)
-Rubber gloves (to avoid fingerprints)
***Note about tools= once a tool (cookie cutters, knives etc) are used for polymer clay, they cannot be used for food---it doesn't matter how well you think you've washed the tool. So make sure to keep your clay tools and your cooking tools separated.***
Step 2: By Hand
You can condition your clay by hand. Warm skin and physically working the clay will make it become softer and easier to work with, however can quickly tire out your hands. When conditioning clay by hand you want to make sure to stretch, roll, and compress the clay. A minimum of 5 minutes is usually enough time to get the clay malleable.
Step 3: Pasta Machine
A cheap pasta machine is a great investment if you work with polymer clay. You'll spend some time running the clay through the machine at different settings, folding the clay and running it through again and again. But it saves your hands from being all achy and at the end, you have a nice flat sheet to work with.
Step 4: Tips
It's usually better to over-condition than under-condition, so if you're not sure, just keep working the clay. A lot of people say that you should condition your clay the same amount of time that it would take to blend two clay colors together. But then, there are other factors.
How much time it takes to adequately condition your clay depends a lot on the type of clay you are using. Sculpey Souffle's are a LOT harder than Sculpey III and so will take a lot more time and effort to condition (which is why I stopped buying the Souffles).
The amount of clay you are conditioning is also a factor, as it's easier and quicker to condition a small amount than a larger amount.
You can also add clay softener, which I have, but haven't tried. Follow the manufacturer instructions for including clay softener but still expect to have to put in some manpower.
If after conditioning your clay is too soft for your purposes, stick it in the freezer---freezing your clay won't affect the conditioning.