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Sunday, March 17, 2013

Clay Test- Baking Times

One of the questions I have heard over and over in my years of workign with polymer clay is “how long should I bake this” This question gets tossed out periodically and everyone seems to have an opinion. Mostly there seems to be two main schools of thought among the clay artists. Those that bake for a long time to make sure their object is cured (I know of a few that bake all their items for an entire hour) and those that bake for just a few minutes. If you have watched me make clay foods you know I am one of the short bakers. We all have our reasons and I think most of us stand by those reasons, we all want to be correct. However, is there an absolute correct?

I decided to approach this question just like I tell my kids to approach questions when they come to them. I've been homeschooling my kids since the oldest was in 2nd grade- he just turned 30. For the most part I have homeschooled for all those years. All but the youngest has attended at least a year of public school at some point or another. The youngest by the way is 14 in case you were wondering. Anyway, when the kids come to a question of this sort I tell them to do an experiment and show the answer.

So now I had a plan, do an experiment but what kind of experiment should I do? How should I set it up?

My first step was to gather up a package of each brand of clay I have- I stuck to pale colors since I figured that would show us if the colors shifted from the long baking process. I then decided to add in the translucent version of each brand also since in most items I make I use a mix containing translucent clay and I know it reacts differently to heat than the other colors.

The brands/colors I am using:
Sculpey III- tan

Fimo- Pearl

Premo- Ecru

Cernit- White (Number 1)

Next I checked what the manufacturers had to say about both baking time and temperature. They varied a bit from Fimo translucent calling for 230 degrees Farenheit to the remainder calling for either 265 degrees or 275 degrees.

Premo called for baking for 30 minutes per ¼”, Sculpey for 15 minutes per 1/4”, Fimo for 30 minutes with no thickness mentioned and Cernit for 15 to 30 minutes again not mentioning a thickness.

I made a few decisions about temperature since I wanted to bake all the straight clays in one batch and all the translucent mixed clays in another single batch I decided to go with the lower temperatures stated for each batch. So I baked the translucent mixed clays all at 230 degrees and all the straight colored clays at 265 degrees.

Next I labeled 2 sets of 5 plates with the following times, 5 minutes, 10 minutes, 15 minutes, 30 minutes and 60 minutes.

I used my pasta machine to make sure I had consistent thickness to all the clay pieces. I rolled all the clays on first the thickest setting and cut out the 5 discs recquired for the test then rolled the rest of each clay to a middle setting and cut out 5 more. I labeled all the discs so that I could be sure of which were which brand. For labeling I simply used a letter stamp to press a letter in the top of each disc (F for Fimo, C for Cernit, etc)

I then baked the plates at the assigned temperature for the time stated on each plate.

After all the plates of clay were baked and cooled I proceeded to check the clay discs. First a visual check of the color of each disc. Was is the consistent between the different baking times.

Next I checked to see how hard/soft each disc was, and at the same time checked to see if they had become brittle.

I think the most surprising aspect of this test is that even though the clay discs had cooled for a couple of hours none of them were really hard. I think leather like is the best description. I have now let them all sit overnight and they are still the same way. Not a single one has hardened up like I expected.

Since the Sculpey III was the one to give the most trouble I am extra glad that I very seldom use it. I have never really liked the way it works up nor do I particularly like the colors of that brand of clay. For the most part I find the colors to be rather harsh compared to Fimo and Premo. I do use Sculpey III when it is the only brand that offers a color I really need, like their Sweet Potato color. I also tend to pull out the Sculpey III when I want to mix with TLS to make frosting, the softer texture does mix much more easily than the more firm clays I normally work with.

Will I change my cooking method, yes, I will probably lean a bit closer to 10 cooking time for things that I want to make more stable. I still will use the shorter times though, I see no reason to cook for longer than I need to and in some cases, since it did cause a color change it would be a real problem.

I may at some point run the translucent mix clay test again leaving out the Fimo and bake at the higher temperature called for on the other brands just to see if the results are the same or change.

So did you learn anything from this test? What would you like to see as a clay test later on? Be sure to let me know what things you would like to see tested in future videos.

Now lets look at those pictures I took of the baked clays:


  1. I don't see this mentioned much but I do this with all clay bakes.

    As soon as timer is up I pop my tray in the freezer for about 5 mins.

    They always turn out solid, I even think they make the item stronger. ;)

  2. I have read about and (and done a few) experiments like this before. I think it is important for anyone using polymer clay regularly to do their own with the clays they most often use. I seldom bake for longer than 15 minutes unless I have a piece with an armature...even then, no longer than 20. And I tend to use a lower temp. The doll makers I know who bake longer, use a lower temp. ("low and slow") and some swear by the freezer or ice bath method for strength.