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Techniques for Curing Polymer Clay

Updated on October 25, 2016

How to Cure Polymer Clay

No subject in polymer clay has more controversy than how to best cure polymer clay. This lens gives an over view of the main techniques used along with their pros and cons to help you make a decision on how to best cure your polymer clay creations.

Safety and Polymer Clay

Safety First

Regardless of what method you use practice proper safety precautions. Never use tools or dishes for food after using them for polymer clay and be careful handling hot items.

Clean your oven thoroughly after baking polymer clay if it dedicated to polymer clay use or if clay wasn't baked in a sealed container like a roasting bag.

Manufacturer's Specifications

What the makers of polymer clay brands recommend.

Super Sculpey

  • Super Sculpey should be cured in a preheated 275° F (130° C) oven for 15 minutes per quarter inch of thickness. DO NOT MICROWAVE. For example, a piece of ½" thickness would be cured for 30 minutes. The layering method is recommended for lager pieces of construction.

Premo

  • Premo! Sculpey should be cured at 275° F (130° C) in a preheated oven for 30 minutes per quarter inch of thickness. DO NOT MICROWAVE. Once cured, the colors intensify and deepen.

Sculpey III

  • Sculpey III should be cured in a preheated 275° F (130° C) oven for 15 minutes per quarter inch of thickness. DO NOT MICROWAVE. If you're unsure whether your piece is adequately cured, try pressing the tip of a fingernail into the bottom of your piece after it has cooled; it will leave a mark but will not actually enter the clay.

Fimo

  • Any home oven is suitable for hardening FIMO. Preheat the oven at 110°C/230°F. Place the FIMO model on an aluminum sheet, and plate or glass sheet and put it in the oven. Depending on the size of the model and the thickness of the walls, the hardening process takes approx. 20-30 minutes. FIMO reaches maximum hardness when completely cool.

Prosculpt

  • Cured at 275° F (130° C), this clay can be used in a household oven. For every 1/4 inch of thickness, it should be cured for 10 minutes.

Kato Clay

  • Kato Polyclay, oven hardening polymer clay, bakes at 300° F (150° C). However, it can also be cured at 275° F (135° C) with good results and has been approved to cure at 350° F by our toxicologist, however caution should be taken when curing at that temperature, time should be limited to 10 minutes as you will run the risk of discoloration. You should never exceed 365° F. In prior laboratory testing, it has been determined that tensile strength increases

Before Baking Any Polymer Clay

Oven temperature dials are notoriously inaccurate. Before you bake any polymer clay you should first find out how hot your oven gets. Set your oven to 275 °F (or whatever temperature your clay needs at it's max point), let it fully preheat for at least 20 minutes, then use a simple oven thermometer (available at any grocery or housewares store) to see where it is at. You can then adjust your oven to find exactly the point on your dial where the correct temperature is.

Ramp Baking

Ramp baking is a technique for gradually baking polymer clay to achieve a hard but minimally darkened result.

Starting at a low temperature of around 175-200° F bake for 30 minutes, increase the temperature by 15-30° and bake for 20 minutes, continue increasing the temperature by 15-30° and baking for 20 minutes after each increase until the temperature reaches the manufacturer recommended temperature. Bake at the recommended temperature for 30 minutes. Allow the piece to cool completely in the oven before moving.

This method requires careful monitoring to make sure the piece doesn't start darkening excessively. Some oven temperatures can spike significantly, always use a separate oven thermometer to monitor temperature.

Under Baking

Under baking is a technique used to try to prevent the darkening that some clays experience. It involves baking under the recommended temperature, usually at around 200° F, for an extended period of time often 1-3 hours depending on the thickness of the clay.

The main risk of under baking is a polymer clay piece which is weak or degrades over time due to the clay not being fully cured.

Over Baking

Over baking is a form of ramp baking used by some sculptors like Casey Love usually with super sculpey to get a very hard result with no cracks. Because the technique causes significant darkening of the clay it's used for sculptures that are to be molded for casting or painted.

Start at 225 and leave the sculpt for an hour, raise the temp to 250 for another hour, raise the temp again to 275 for 2- 3 hours or until the Super Sculpey has truned a dark caramel or even as dark as a redish brown brick color. Shut off the oven and leave the sculpt to completely cool down before removing the sculpture. If you are baking a rather thick sculpture use the same method above but raise the temperature slower and in smaller incraments.

The main risk of over baking is potential emission of small amounts of hydrochloric acid gas which can irritate the eyes, throat, and lungs. Burning can also occur.

Toaster Oven - This is the model I use and it's great!

Hamilton Beach Convection Toaster Oven
Hamilton Beach Convection Toaster Oven

This toaster oven has a 15 minute timer. I've found that for beads and pendants that two cycles of the timer (30 minutes) is just about perfect. It has a constant bake setting too but I like using the timer because it automatically shuts the oven off. It's size is best for small objects (6 inches or less) if you routinely make large pieces you'll want to get a larger model.

 

Using a Heat Gun

Heat guns can be used to cure small polymer clay pieces or to partially cure a sculpture to harden an area to protect it from damage while working on the rest of the sculpture. Heat guns are not suitable for completely curing large polymer clay pieces.

To use a heat gun turn it on either a low setting or if it has a dial set it as close to 275 degrees as you can. Aim the heat gun at the piece and keep constantly moving to prevent burning. Watch for the surface to go dull and darken slightly to determine if the clay has cured.

Heat guns take practice to effectively be used for polymer clay and they are the most unreliable of all curing techniques. Burning, bubbling, and blistering of the clay can occur if care isn't taken. Practice on scrap clay first to get the technique down. Always use a heat gun in a well ventilated area.

Boiling Polymer Clay

Gently boil small polymer clay pieces such as beads either in the microwave or on a stove top for at least 15 minutes and up to 1 hour. You must completely cover the clay with water or you risk over heating and other problems.

There is some debate about whether boiling completely cures polymer clay especially for items larger than beads.

Poll!

What's your preffered method of curing polymer clay?

See results

Miscellaneous Curing Tips

Here are a few helpful hints for baking polymer clay using any of the baking methods.

  • To reduce temperature spikes in toaster ovens lay small ceramic tiles or pieces of broken ceramic such as from a terracotta flower pot in the bottom of the oven. The pieces of ceramic absorb and then radiate heat helping to keep the temperature even.
  • If you have to use a kitchen oven for curign your clay, encase it using a covered baking dish or roasting bag to reduce any build up of residue on your oven walls.
  • Lay polymer clay pieces on polyfil batting to cushion pieces so the bottom does not get flattened shiny spots.
  • For sculptures with areas of thin and thick clay protect the thinner areas from darkening more than the thick areas by covering them with aluminum foil.

Reader Feedback - Let me know what you think!

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    • profile image

      gods_grace_notes 9 years ago

      Hi Sheryl,

      I really enjoy polymer clay, but am still a beginner. Therefore I have only cured my works following manufacturers instructions. I had no idea you could boil the clay!

      I love your jewelry, and will fave this lens for reference. Great job!

      Connie

      : )

      Welcome to Connie's Craftaholics Club!

    • profile image

      anonymous 8 years ago

      Wish that these tips for curing had been available back when the polymers were introduced!

      Thanks for another great lens!

    • JudyDunn profile image

      JudyDunn 8 years ago

      Great lens, except for the part about boiling the clay to cure it. Boiling water will only reach 212 deg. F. It can never get to an adequate temperature to cure the clay so that it is strong and durable.

    • Sheryl Westleigh profile image
      Author

      Sheryl Westleigh 8 years ago from Maine

      I'm just covering the common techniques used and plenty of people have good luck with boiling. I did put a disclaimer in bright red letters about the debate over whether if is durable in the long term. It's up to individual artists to decide what to use.

    • profile image

      AbbyJ 8 years ago

      Great lense, very informative, I learned a few things I didn't know which is always useful! Also, love your jewelry, especially your cuttle fish necklace, I love those clever little critters!

    • aperkins lm profile image

      aperkins lm 6 years ago

      Thanks for the lens! Never knew there were so many ways to bake sculpey.

    • junecampbell profile image

      June Campbell 5 years ago from North Vancouver, BC, Canada

      I've been told that a Ranger melting pot always works for baking polymer clay. Do you have any thoughts on this?

    • KireinaJeweller1 profile image

      KireinaJeweller1 5 years ago

      l can never make up my mind how to do it. At the mo baking it in a halogen oven.

    • Barbara2659 profile image

      Barbara2659 4 years ago

      I love this lens. Thanks for accumulating all the sites I can review!

    • KireinaJeweller1 profile image

      KireinaJeweller1 4 years ago

      l use a halogen, but l have terrible problems getting thinner pieces to cure very hard so they don't snap in half when l test them. This drives me nuts. Thank you for this lens - very interesting and informative. My jewellery tends to be chunkier, but l am scared of doing more delicate flowers etc... because l can't get the clay to cure well enough. Again thanx

    • profile image

      daria-queenly 4 years ago

      I need help!!!

      My fimo clay the yellow one..TURNS SOOO dark all the time

      I just use 100 degrees (swedish) and it still dark after 15 min the oven

      i need some serious help with this

      i want it to be yelllow a sharp like it is before i bake it

    • Sheryl Westleigh profile image
      Author

      Sheryl Westleigh 4 years ago from Maine

      @daria-queenly: It could be that your oven's temperature settings aren't accurate, test it with an in oven thermometer to make sure it isn't running hotter than it should. You can then adjust your oven until the thermometer says 100 degrees and try baking your clay again. If it is still darkening the clay I'd try baking at a lower temperature for a longer period of time, this can sometimes result in a piece that isn't as strong though.

    • centralplexus profile image

      centralplexus 4 years ago

      @daria-queenly: Well, when you bake polymer clay it ALWAYS gets darker than the "raw" clay. Some brands baked color is closer to the unbaked color they have, but no polymer clay will remain unaltered colorwise. I hope you're not using a grill oven, are you?? If so ,there's your problem. Even at low temperatures the grill will overbake/fry your clay quickly .Check your oven and its settings, and if you can't deactivate the grill consider getting a small oven specifically for your clay projects. Hope this helps!

    • profile image

      nonya222 3 years ago

      Thank you for some great information. Very helpful.

    • profile image

      Kaleo-Wilson 10 days ago

      Hello,

      Before baking any Sculpey clay, I was curious what kind of container should I use - I'm wanting to sculpt a 1 1/2 to 2 ft tall figure.

      We only have a gas oven and it's currently used for cooking. So to keep any 'chemicals' off of the walls ... Would a turkey bag be best? Or would it 'damage' the sculpt-to-be somehow?

      Any other helpful tips would be awesome too. Simply trying to research prior to starting =]

      Thanks again!

      Angie W.

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