How and why do you need to leach clay? What does that mean, anyway? As you know, “leaching” means to draw out a (material) from another…in the case with polymer clay, “leaching” refers to the removal of some of the plasticizer from the material. Yes, this same component that is able to permanently take shape in the oven, is also the same material that creates the soft texture.
Have you ever worked with clay that was too soft? I mean, it’s nice when you’re in the kneading stage and all, but when you’re trying to get it to do certain things, the softness can work against you. You may notice this if you’re cutting shapes and trying to get them edges or seams to be very precise.
Polymer clay needs to have a certain amount of firmness to it so you are able to cut out parts without worrying about them becoming “mushed up” when you try to apply them to other parts of a design. “Mushy” clay parts can be a real bummer, especially if there are different colors involved, and those colors can bleed together and you end up with …results you may not like.
So let’s take care of that right now. How do you “leach out” the excess softness of polymer clay? It’s actually the plasticizers present that we want to draw out – but we don’t want to go overboard with this, either, lest your clay batch may become more of the opposite – too stiff. So there’s a delicate balance to be maintained.
This is why we always work with it on wax paper, which has a slippery surface that clay won’t bond to -for the most part, it may stick a little, if it’s wrapped in the paper long enough it may discolor the paper.
Anyway, take your clay batch and roll it as usual onto a piece of paper like this. Try to get it as thin as possible, close to a fourth of an inch thick.
Cover this with another piece of paper. Now take a look around for something heavy – it can be a hardcover book, stack of magazines, or similar – and place on top.
Let it sit for awhile…check it after about 15 minutes. Although it could take a little longer.
I checked my computer clock after about 20 minutes to see, and it looks like this. You will see a light stain or outline of the rolled out clay slab. If it the plasticizer has been properly leached. this is what you can expect. It’s not “greasy” or anything, even though the clay is oil-based – this is the result of the plasticizer being absorbed into the paper.
Not too different from the process of skimming off excess fat from beef stock, ground chuck, or something else culinary-related, right? That’s because it is.
If you don’t see anything yet, give it a little more time – replace the piece of paper and heavy object and let it sit for another 20 minutes. I wouldn’t go for any more than an hour, if it still doesn’t leach out you may just have a bad batch of clay. Which does happen.
Now your clay is ready to do whatever you want to with it. Follow this approach every time you need to firm up your clay for something professional, like jewelry, or if you’ve got a batch that just won’t cooperate.