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As I mentioned in my IPCA retreat wrap-up, Polyform (the makers of Sculpey, Studio by Sculpey, Premo, etc.) sent their chemist, Kim, and their education manager, Iris, to hold a question and answer session. This session was very popular with the attendees and extremely valuable to me. Here are the highlights of the discussion:

  • Every batch of each color and type of clay is tested multiple times to ensure it's within acceptable ranges. BUT they err on the softer side when they manufacture the clay, because it can age over its 6-month distribution and warehousing time. The hardness of the clay when you get it depends on how long it took to get to you.
  • Polyform only ships Monday through Wednesday in the summer months so the clay is less likely to get partially baked in transit. Still, once it's out of their hands, they can't control where (i.e., an un-air-conditioned warehouse) or how long it's stored.
  • If the clay is too soft when it gets to you, they recommend leaching to get rid of the extra plasticizer. If you leach too much (or if it's too hard), add Mold Maker or clay softener to give it more flexibility. I've always wondered if this kind of tweaking hurts the strength of the clay. The chemist said that while leaching too much could hurt the strength, it should be fine if you crank up the temperature and make sure it's baked properly.
  • The higher baking temperature was a recurring theme. While the package temperature (275°) seems to be the company's officially-recommended "safe" temperature, they said you'll get stronger clay if you bump it up another 10-20 degrees. Interestingly enough, they had also tested the Fimo clays using both the old higher and new lower temperature recommendations. They said it was stronger at the higher temperatures.
  • Phthalates came up several times (surprise, surprise). All of Polyform's clays except Studio by Sculpey are now phthalate-free. (Interesting tidbit: they've already had to spend $50,000 this year testing and certifying their products.) The chemist said that phthalates have been used for a long time (100 years, I think), and were not a risk... that basically they were the latest victim of a witch-hunt. (See this older Polyform document for safety info on phthalates). She said we will start to see a reduction in the clay's shelf life now that the phthalates have been removed.
  • Another safety concern that people asked about: baking in your home oven. The chemist said that the residue you find in your oven is a plasticizer. While there are no "toxic fumes" unless you burn your clay, she recommended opening a window while curing, or using your oven vent. Try a turkey basting bag or covered pan if you're using your regular home oven.
  • They recommended curing TLS at a higher temperature for clarity. They also said that Bake and Bond is different that TLS: it's thicker, so it works more like a glue.
  • The "moonies" in translucent clay are caused by moisture and trapped air.
  • Clay colors aren't UV colorfast. If you want to use it outdoors, get a marine varnish.
  • Polyform has a designer endorsement program for published projects using their clays. They also have a program where guilds can receive clay for lessons. In both cases, you must use only their clays (no competing products).
  • They encouraged us to contact their customer service department for any product questions or problems. They try their best to answer any questions that come in.

I was very impressed with Polyform for doing this. They were the only clay company that came to the retreat (we thought Pardo was going to be there, but the "word on the street" is they decided there weren't enough attendees to make it worthwhile). Having a no-holds-barred Q&A session seems like a risky thing for a company to do, but I think most people came away with a new respect for them. And while we've heard some of these things (like the leaching recommendation) tossed around on message boards and forums before, it's nice to hear them officially from the experts.


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Great info, good to know. I'm impressed they did this Q & A session for everyone. Thanks for sharing the highlights.

Thank you so much for this. It is so helpful to know that I can let the heat get above 275. I have been so careful to keep it at exactly 275 with an oven thermometer, preheating and adjusting for a long time. This will make things so much easier!

Do be careful, though, Marilyn. There is an upper limit at which the clay definitely will burn & cause those "toxic fumes." I don't think the Polyform people mentioned a specific temp on that, but I've always heard it's 300°.

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