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Topic: help please with cooking times on projects using a mix of different clays...  (Read 874 times)
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« on: May 31, 2008 12:32:29 PM »

ok so i have fimo and premo sculpey and sculpey says to cook for 30 mins per quart of inch so if i had a project an inch thick this would take me two hours to cook and fimo says just to cook for 30 mins i cannot see anywhere that states about the thickness for cooking fimo just the specific cooking time of 30 mins and not to over cook it well im wondering then if i done a project that was using a mix of both of these clays what would i do about the cooking time, say if cooked a cake an inch high (the thickness) and was using both clays would i go with the sculpey instructions and cook for the two hours or the fimo instructions and cook for just 30 mins and risk undercookoing it, how do you come up with good cooking guidelines any help much appreciated
« Reply #1 on: May 31, 2008 03:00:26 PM »

Your post is a bit confusing but, make whatever you are making, take a moist paper towels put one on the bottom of your baking suface and on top of your object. When they dry out repaet the process. Ive done this and left things in the oven for a very long time with out them burning-it actually makes them stronger.
Diane B.
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« Reply #2 on: May 31, 2008 06:50:03 PM »

Baking temps can be quite problematic, especially these days since the new formulations of the Fimos have come out with their new recommended temp of 230 instead of 265.  Other clayers have found that it's okay to use the old temp though instead of the new one, especially if one is baking "carefully" (with an oven thermometer, not close to the coils or sides, on a good baking surface, etc.). 
However, there is a problem with the Sculpeys* even at their recommended temp (275) since they tend to darken very easily, compared to other brands baked at their recommended temps... Polyform doesn't really address this issue because they know the higher temp is really required for strength and they think that "crafters want to bake quickly." 
Using a partly-"enclosed" or a fully-enclosed baking method can keep even any of the Sulpeys from darkening though (one of which is to drape a damp paper towel over the object while curing, as mentioned above).

"the Sculpeys" are mostly Sculpey, SuperSculpey, and Sculpey III -- Premo isn't a "Sculpey" to most clayers because it is a quite different clay, and was created to the specifications of a clayer with the Polyform chemist simply carrying out her wishes

Baking times are also a bit weird. 
It used to be that all the polymer clays gave the 15-20 minutes per quarter-inch recommendation, but for much thicker items it really doesn't take as long as the math would suggest.  On the other hand, any polymer clay will get stronger than it normally would have with longer baking because the polymerization will continue and continue.  (Time and temp. are interdepent for thermosetting plastics like polymer clay, so the lower the temp the longer the baking required to achieve sufficient polymerization--there's even an equation for that relationship).

As for mixing clays, the general advice was always to decide on the temp based on the relative amounts of each brand used in a particular mix.  But it's actually better to bake them all at say 265-275 for as long as is possible without causing the mix to darken (which can be helped with the techniques mentioned above).  If you bake at a lower temp (230, e.g.) then you'll certainly need to bake non-Fimo clays longer to get a good amount of polymerization --which btw isn't just when the clay feels hard, because the outer portions of the clay will polymerize sooner than the interior will so you wouldn't have any way to know that the item hadn't polymerized well all the way to the center.

If you want much more info on all aspects of baking polymer clay, check out this page:

Diane B.
« Last Edit: May 31, 2008 06:59:09 PM by Diane B. » THIS ROCKS   Logged

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« Reply #3 on: June 02, 2008 01:09:11 PM »

You do not have to cook it that long. I have been working with polymer clay for 19 years and mostly using Fimo. I have never baked anything more than 45 minutes no matter how thick it is and I have never had a problem. I did not feel that it was any more breakable either. I would fire the mixture of clays at the lower recommended temperature the other clay will be fine just fire it a little longer. Good luck!

« Last Edit: March 02, 2012 03:42:23 PM by jungrrl » THIS ROCKS   Logged

« Reply #4 on: June 03, 2008 08:17:42 AM »

thank you so much for the advice ive made a few bits with a mixture of the clays just scared to cook them now oh well guess tis trial and error but thanks so much for your advice it has helped me heaps
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