How to Harden Modeling Clay

Modeling clay isn't meant to be dried or hardened. Modeling clays contain oil along with regular clay. These oils make them impossible to harden, and trying to stick them in the oven — like you might with regular clay — would cause the clay to melt into a puddle. Modeling clays were designed to be like this, however. They were meant to be worked with the hands, sculpted into a model for inspiration, and then broken down before assuming a new shape. If you happen to have one of the following clays and want to harden it, however, see Step 1 for more advice.


  1. Image titled Harden Modeling Clay Step 1
    Identify the kind of clay with which you're working. Common kinds of clay include polymer clay (often called oven-hardening clay), self-hardening clay and fine art clay. Since the type of clay has an equally powerful effect on how you build your model, this is something you're better off knowing before you begin your projects.
    • Polymer clay does not technically contain clay. Instead, it has polymers similar to PVC, with liquids added to make it moldable. It hardens usually in an oven over low heat.
    • Self-hardening clay is exactly what it sounds like. You mold it, set it aside, and let it harden over the course of several days. Unlike modeling clays, which are oil- or wax-based, and polymer clays, which are resinous, self-hardening clays are water-based.
    • Fine art clays are usually exactly like self-hardening clays, except that they use high-quality clay and add only water.
  2. Image titled Harden Modeling Clay Step 2
    Apply any pigments or glazes appropriate for painting on prior to hardening the clay. Some pigments are applied after the clay hardens or in the middle of the hardening process.
    • It's important to understand these aspects of any coloration prior to starting your project.
  3. Image titled Harden Modeling Clay Step 3
    Bake polymer clay and oven-hardening clay in a regular kitchen oven. Set a piece of wax paper on top of a baking sheet, cutting it so that it matches the inside dimensions of the sheet.
    • Most polymer or oven-based clays will harden after they are cooked at 265 °F (129 °C) to 275 °F (135 °C) for 15 minutes per 1⁄4 inch (6.4 mm) of thickness.
    • Remove the baking sheet from the oven, and place it on a heat-resistant surface. Allow the clay items to cool at room temperature before removing.
  4. Image titled Harden Modeling Clay Step 4
    Use patience when waiting for self-hardening clay to harden. Keep it out of the way and trust time to do its work.
    • Set the finished model on wax paper on a baking sheet or similar flat and stable surface.
    • Place the sheet someplace dry, at room temperature and out of direct sunlight. For best results, set it out of the way of other activities. The top of a refrigerator is a good example.Wait 7 to 10 days for the clay to dry completely.
  5. Image titled Harden Modeling Clay Step 5
    Schedule time in a professional kiln to harden fine art clay. You can find these facilities at local art stores, community colleges and community centers. If you're not already intimately familiar with how to kiln-harden clay, let the people who run the kiln fire your model.


  • Always leave a breathing hole in any clay model that contains a bubble of air. Otherwise, the expanding air can crack your model, or even make it explode, during hardening.

Things You'll Need

  • Clay model
  • Wax paper
  • Baking sheet
  • Oven

Article Info

Categories: Clay Projects