There’s nothing more frustrating than spending ages handcrafting a miniature masterpiece, just to have it break or crack either during baking or once it’s cooled.
Why does polymer clay break? The number one reason polymer clay models break is down to the temperature they’re baked at and how long they’re baked for. If polymer clay is not baked for long enough, or if the oven is not at the correct temperature, then it’s more likely to break:
- The thicker the piece of clay, the longer you’ll need to bake it for
- Most packets of clay will suggest the clay is baked for 15 minutes for every 1/4 inch of clay. So measure the thickest point of the clay and multiply every 1/4 inch by 15 to get your overall bake time.
You could even bake your model for an extra 15 minutes or more provided your oven is at the correct temperature. Baking polymer clay for longer will make your model harder and your model won’t burn, unless your oven is too hot.
Remember that polymer clay is only fully cured once it’s out of the oven and cooled completely, it’s more likely to break if it’s knocked or dropped while it’s cooling down.
There are of course many other factors to consider to get a sturdy non-breakable polymer clay model:
- The brand of polymer clay you use – some brands of clay are stronger than others.
- How thin your polymer clay is – very thin clay is more likely to break.
- How well conditioned your polymer clay is – clay should be very smooth and flexible when it’s fully conditioned.
- Other ingredients or embellishments included in the clay.
- Whether you’ve blended different brands of clay together – this can affect the overall baking times and lead to under-baking your clay.
- Air bubbles in the clay – these could cause areas of weakness.
What Are The Strongest Brands Of Polymer Clay?
Crafters swear by Kato Polyclay for a strong and durable clay. Kato Polyclay is create specifically for artists by polymer clay artist Donna Kato. It’s quite stiff, so can be difficult to condition but the results once properly cured are extremely strong.
Sculpey Souffle, Sculpey Premo and Fimo Professional are all also excellent choices for strong, long lasting models once properly cured.
Now, onto brands to avoid, some brands have a reputation in the crafting and modelling worlds of being a bit flimsy and easy to break, even after being properly cured.
If you’re baking a very thin piece of polymer clay, then you might be best steering clear of the following brands – Super Sculpey, Sculpey III, Bakeshop and Craftsmart. These are renowned in the polymer clay community as not being the toughest clays for very thin projects.
How To Stop Thin Pieces Of Polymer Clay From Breaking
The thinner your clay is, the more likely it is to break, so choosing a sturdy polymer clay like Kato Polyclay is your best bet against breakages. If you use a strong, well conditioned clay and then bake it for the right amount of time, then even the thinest piece of clay shouldn’t break.
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Conditioning Clay Properly To Stop It Breaking
Polymer clay that isn’t properly conditioned is more prone to breaking while it’s baking.
There are three reasons why conditioning polymer clay properly helps to make it stronger and less prone to breaking:
- It helps to remove air bubbles – air bubbles can create points of weakness and also ruin the overall look of your finished model.
- It helps to thoroughly mix all of the clay ingredients – polymer clay is a made of a polyvinyl chloride (PVC) base which is the same material that thousands of plastic objects are made from – from children’s toys to garden hoses. As polymer clay is a flexible PVC, it’s mixed with a number of other ingredients to make it pliable. These include liquid plasticisers, stabilisers and pigments to give the clay its colour. If these ingredients aren’t properly mixed through conditioning the clay, you might find your clay has areas of weakness that could make it more prone to breaking.
- It helps make the clay stickier and therefore more likely to bond, even if you’re making very thin pieces.
Once conditioned properly, your clay will feel super smooth, flexible and be easy to work with. Conditioning clay will also mean it’s less likely to crumble when you work with it.
Embellishments And Inclusion That Could Cause Polymer Clay To Break
Adding anything to polymer clay will increase the risk of it breaking, as clay on its own is much stronger. For example, adding embellishments such as glitter to your clay, will make it harder for the clay to bond with itself as the glitter particles will be in the way.
As an experiment, I added glitter to a chunk of clay, rolled it thin and baked it alongside another piece of clay that didn’t have glitter included in it. As you can see from the results, the polymer clay with glitter in it broke much more easily than the piece without the glitter included.
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Another thing to look out for is any material you use inside your clay could make it more vulnerable to breaking, unless it’s thoroughly dried before you include it. The heat from baking your polymer clay will turn any moisture into steam which could swell the clay and make it weaker, or break it during the baking process.
How Mixing Brands Of Polymer Clay Could Lead To Breakages
Many crafters choose to mix clay to create custom colours, or to use up small pieces of clay. There’s nothing wrong with mixing brands but it can affect how long you need to bake your models for, and if you under-bake them, this could cause the clay to break.
Different brands of clay have different baking times, if you’re mixing two brands of polymer clay, then bake your model for the longer recommended baking time. Ideally, bake your mixed-brand miniatures for at least 30 minutes at the recommended temperature which, for most brands, is 130 degrees centigrade (275 Fahrenheit).
Under-baking is one of the top reasons why polymer clay breaks, so if in doubt, bake it for a little longer than the recommendation on the packet. As long as you have the correct temperature (using an oven thermometer), your model won’t burn.
Further Questions
How do I know if I’ve baked polymer clay for long enough?
You’ll know if your clay is baked long enough as you should be able to bend it after baking. Polymer clay that hasn’t been cooked long enough will break after it’s baked.
Top tips for better polymer clay baking:
- Use an oven thermometer to make sure your oven is at the exact right temperature and bake your clay to ensure the thickest point of your model is thoroughly baked.
- Polymer clay bakes from the outside in, which means if you don’t bake it for long enough, the middle will be under baked, causing the model to be brittle.
- Most brands recommend baking polymer clay for 15 mins per 1/4 inch, so measure the thickest point of your model and bake it for as long as required. For example, if your model is an inch wide, you’ll need to bake it for an hour.
Does Quenching Make Polymer Clay Models Stronger?
Some crafters swear by quenching polymer clay models to increase their strength. The idea is that you put the models straight into ice water as soon as they’re out of the oven and this rapid cooling will make them more durable and less likely to break.
Although this won’t do any harm to your models, there’s no evidence that this actually works to made polymer clay stronger. In this video you can see how quenching and not quenching makes no difference to the strength of two pieces of baked thinly rolled polymer clay.