How to Leach Polymer Clay

Have you ever opened a brand-new package of polymer clay and it was so soft, sticky, and goopy that it was almost liquid? It’s easy to assume that you got a defective bar or that the brand is just too soft. Not at all! Most polymer clay is very soft when it’s fresh from the manufacturer. There’s nothing wrong with it! But the softness can also mean that it’s difficult to use without some adjustments. One of the most valuable skills that a polymer artist needs to know is how to leach polymer clay. But…what does it mean to leach polymer clay?

You can leach polymer clay to make it more stiff by using paper to absorb some of the excess oils and plasticizer.

What is Leaching Polymer Clay?

Polymer clay is a vinyl putty that contains powdered PVC, plasticizer, pigments, and various oils, waxes, and fillers that allow it to be worked. When the ratios of these components are in the right balance, the polymer clay is a dream to handle. But when there’s too much of the oil or plasticizer, the clay can be soft, sticky, or even runny. If you can blot out some of the oils by leaching your polymer clay, it will be much easier to work.

Sheets of polymer clay between two sheets of paper, pressed to remove oil and make the clay stiffer.
Leaching polymer clay to make it less soft and goopy.

How to Leach Polymer Clay?

It’s a simple process, and there’s no way to do it wrong. Here’s how you leach polymer clay.

  1. Get some plain, unprinted copy or printer paper. The cheap stuff is fine.
  2. Roll your piece of clay out into a thin sheet, maximizing the surface area.
  3. Lay the sheet of clay on a sheet or two of paper.
  4. Cover with more paper.
  5. Sit on it (my favorite method). Or set something heavy on it.
  6. Wait.
  7. Check on the sheet. Leach longer if necessary.
  8. Mix the clay thoroughly.
  9. Repeat if necessary.

The paper will absorb the oils from the clay sheet, leaving it stiffer and easier to work. Make sure to check often, though, because some clay brands (particularly Cernit Pearl and Cernit Metallic) will leach very quickly and become too stiff. I only leach Cernit Pearl for 3 minutes! Other brands, however, may need to be leached overnight. There are no rules. Check your clay often and give it what it needs.

A sheet of paper with an oil spot and a sheet of polymer clay that is being leached to make it less soft.
The oil from polymer clay can be leached out with paper, leaving an oily spot on the paper.

Why Does This Happen?

If the clay is so soft, why don’t they get the mixture right at the factory? Why don’t they make it stiffer from the beginning? They could, but then the clay would be too stiff later on. And it’s MUCH easier to deal with soft clay than clay that is too hard and crumbly. You see, the PVC in polymer clay will continue to absorb the plasticizer over time. You know how leftover pasta is always dry because it continues to absorb the sauce? Polymer is the same way. Straight from the factory, the clay is at its “wettest.” But over time, the clay will “age” and become much more workable. The clay you buy now that’s too soft will be perfect in six months or so. The only reason you’re seeing this extreme softness now is because of the clay shortage. Nothing has been sitting in warehouses for long now. In some cases, you’re getting it mere weeks from the production line.

Paper sheets with oil spots from leaching polymer clay.
These sheets of paper were used to leach polymer clay. Note the oil spots where the clay was left in contact with the paper.

Tips for Leaching Polymer Clay

You’ll become more familiar with leaching, which will become a valuable skill in your “tool kit.” Here are some tips that might help.

  • Make the clay sheet pretty thin. The more surface area you can expose to the paper, the faster it will leach.
  • Don’t leach the whole block. Start with half of what you need. Then, if you over-leach, you can mix with the un-leached block, and they’ll balance out.
  • Don’t use printed paper. The printing will transfer to the clay’s surface. (Yes, this is how image transfers work.)
  • You’ll see an oil spot on the paper when you’re done. That’s the oils from the clay. You can discard the paper when done.
  • Mix the clay thoroughly after leaching because only the outside of the sheet will be leached. The inside part will be “wetter”.
  • If you over-leach your clay, it’s not ruined. Add a drop or two of clay softener such as Sculpey Clay Softener or Cernit Magic Mix.
  • If the clay sticks to the sheet, release it by sliding a long blade between it and the paper.
  • Don’t leach the whole block if you won’t use it soon. Remember that the clay WILL stiffen up with time on its own.

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5 thoughts on “How to Leach Polymer Clay”

  1. I loved ow you began this article by assuring us that it’s not our fault! Great advice. I’m still waiting for someone to invent a “Leachometer” – a simple device, maybe like litmus paper, that shows if your clay is leached properly. I’d love to have confirmation that all my clay was in a similar state before beginning a project!

    1. Well, there are no standards for this though. Some people like their clay very stiff, others like it quite soft. The beauty is that you can adjust the softness yourself for each project.

  2. For leaching Sculpey Premo, I use the backs of printer paper that I have used before, primarily the back of New York Times crossword puzzles so I am not wasting paper. The ink does not bleed through. Thanks for the tip about Cernit.

  3. Thanks for the leaching tip. I just bought Cernit which is quite sticky.
    If I hadn’t read this I would probably have avoided buying more.
    Sharon B

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