Thursday, January 26, 2012

Preparing polymer clay for casting molds

This is the first of a series of tutorials for those interested in the details of making their own molds for casting paper. 
This method was developed specifically (by me) for working with calligraphy, but is adaptable to many sorts of designs. I've been refining and expanding it for many years and have taught many calligraphy guilds and at several international lettering arts conferences. To see some examples of papercastings, go to the gallery on my website:papercasting gallery

Polymer clay is an outstanding medium for making papercasting molds. It keeps fine detail, doesn't change at all when baked, and releases the paper cleanly without needing mold release agents which are usually non-archival.  Sculpey Premo has proved to be the best choice for this technique, due to its strength and flexibility. It is by far the most economical in 1 lb. bricks.

You will also need a roll of waxed paper on hand.

White is a good choice as your design will show up well and it is easy to tint with small bits of other colors when desired.

First of all, the clay must be "conditioned" as the various chemicals separate over time, and to make it more malleable. The easiest way is to break or cut it into chunks (no bigger than the little 2 oz packs) and hand them to your sons (who are watching a football game) to knead. The next easiest method is to warm and flatten in your hands until it will go through a pasta machine at the widest setting.

As you fold and re-roll it will gradually become softer and well-mixed. It is well worth the moderate expense of buying a pasta machine if you are going to work much with polymer clay, especially for casting molds that take thin layers which are very difficult to roll out by hand.
*You should not use a pasta machine for food if you use it for polymer clay.

If you are not sure of how much to condition it, try mixing colors and when the color is completely even you know you are done. Don't worry if it breaks into bits at first, smash it back together and keep rolling through.
Keep folding but never roll with the fold last as you can add air bubbles. Every time you roll you need to be conscious of avoiding getting air trapped between the layers - usually folding in thirds to enclose rough edges and rolling with the folds perpendicular to the rollers will work well. If you think you have a bubble, prick it with a pin. Even when your mold is almost done you can still do this and gently smooth over the pinhole.

Tinting is very useful for making complicated molds with various depths as the layers of color help guide you in figuring out which parts to cut out in each layer.

When it is nice and workable you can start dialing down to the thickness you want. Make a habit of always having waxed paper under your rolled clay.

Every time you move things around you want to move the waxed paper with clay on it, not lift (and stretch and deform) the clay you have so nicely rolled out. It also protects whatever is underneath, since an oily residue leaches out of the clay over time.

If you are making a mold with several layers you want to work the clay quite thin - usually the thinnest setting doesn't roll smoothly or hold together well enough, but about the second or third will do fine. For background layers or very bold designs you can stick with the thickest setting. It may take some experience with cutting to know for sure - it seems thicker when cutting than it did when rolling. Start with very clean and simple designs (*upcoming tutorial on choosing and adapting designs).

Next time: joining strips of clay to get a piece large enough for your casting design.

remember, live classes are available - go through the entire process; first a day of small projects to learn several techniques and see the results, then discuss how to plan successful casting projects using your own art and a day to do a big project with plenty of individual attention, classes that meet a third day (or half) get to see the test castings, learn how to fix problems in the mold, work with color, learn about 3-d possibilities, and more) -  click here for information on workshops


  1. Looking forward to reading your blog posts. When I was experimenting with this a couple of years ago (after you had kindly sent your instructions to me), I could never get rid of all the bubbles that formed in between the layers in the pasta machine. Maybe I should give it a try again!

  2. Thank you so much for sharing such good instructions. Greetings from Sue in South Africa.

  3. thanks for the tutorial-looking forward to next installment!

  4. I am so thrilled to hear that you are sharing your information with us. I tried to register for a class with you at the last conference. Unfortunately it did not have enough people.

    Thank you so much for sharing your information,
    Pam in Kelowna, British Columbia, B.C.