Wednesday, April 30, 2008

Moonies in Polymer Clay

“Moonies” in Polymer Clay sculptures

What is a “Moonie”? A moonie is a bubble of air that gets trapped in the polymer clay and when you bake your piece, it will show as a whitish spot in the form of a half moon or a bump in a lighter color. That’s why they’re called “moonies”
The moonies are attributed to different factors:

Preparing and handling the clay
Sculpting with an armature
Sculpting without an armature
Smoothing the clay

Preparing and handling the clay:
When get your clay it comes in a 1 pound brick, so you should cut it in small pieces and pass it through the pasta machine. When you’re done, you’ll have thin layers of clay that you will use to make your sculpture.

I used to pass and pass the clay through the pasta machine. When you are using only one kind of clay, there’s no need to do this. The more you handle the clay, the more air bubbles will get trapped in and more moonies you’ll get.

The best way to prepare your clay is to make thin slices, then pass it through the pasta machine once or twice. Let it rest on waxed paper and then use it whenever you need it.

Sculpting with an armature:
When you sculpt with an armature, make sure you press the clay into the armature, as hard as you can. If you see an air pocket or a gap between the armature and the clay, either punch it, open it or press the clay in.

When you are applying the subsequent layers of clay, just make sure that you don’t leave any spot without pressing firmly.

Sculpting without an armature:

When you sculpt without an armature, I would advise you to use a larger piece of clay and if possible, don’t pass it through the pasta machine. Just make a ball, pressing the clay as hard as you can between your hands. Then shape it into anything you want. If you see a small pocket of air when you’re sculpting your piece, pierce it immediately and fill the hole or gap with clay until the air bubble is gone.

Smoothing the clay correctly is a very important step so that your piece can be free of moonies. I used to smooth back and forth, pushing the clay up and down and side by side. By doing this I was disturbing the clay that was already set, from one place to another and creating air pockets or bubbles.

Smooth in one direction with small pats instead of dragging your fingers. If you must drag, then do it softly and again, in one direction. Use smoothing oil so that it is not that hard to slide your fingers.

This has been a subject of disagreement among the sculptor’s community. The clay comes with instructions and most of them say to bake 1/4 of clay at an oven temperature of 265 degrees fahrenheit for 20-30 minutes.
So, if you have 1” of clay (that’s 4 layers of 1/4 each) you would have to cook from 1:30 to 2:00 hours, and so on. Right? Wrong!

I started using this math to bake my pieces and to my disappointment my sculptures came out burnt and full of moonies. I called the three leading polymer clay manufacturers to ask their engineers about this issue and honestly they didn’t know what to answer. One of them said “just to use 1/4 of clay at a time” Other one said: This is not possible. The clay would not be properly cured for sure and the sculpture would break” But what if you are creating a miniature sculpture of 6” long?

It was obvious that the temperature was too high, heating the air bubble faster than the clay, hence forcing the bubble to expand. It made a lot of sense to me, because I was sure that the air would heat faster than the clay... So what If I baked at a lower temperature for a longer time? I analyzed that by increasing the curing time, the time would make up for the high temperature, so my piece would not only be completely cured, but it would be free of moonies too, and to my amazement, it was!

How did I came up with this? Well, we never cook a Thanksgiving or Christmas turkey the same time do we? We have to take in consideration the bird’s weight and then we say we’ll cook it at 350 degrees fahrenheit for 1 hour per every 3 pounds so if our turkey weighs 22 pounds, we’ll cook it for 7 hours approximately.

So based on this thought, I baked 1” layer of clay at a temperature of 200 degrees during 3 hours and it worked! My baked piece was free of moonies, completely cured and hard. Then I made an experiment with a 2” layer of clay baking at 200 degrees during 5 hours and it came out perfect.

Now these calculations are not mathematical neither exact, much less the only ones. This is what has worked for me. So I shared my experience at one or two polymer clay forums and it was a debate. Some agreed with me and have been already doing it and others didn’t agree and swore our pieces were going to break. So far the sculptures are in one piece and I have never burnt another sculpture.