white-baking-duration
Circles on top are raw clay. Kato and Fimo were double-baked in the left column and baked normally in the right column.

What happens when you bake polymer clay multiple times?  Sometimes I make projects that require multiple bakings, so I wanted to know.

All the squares and rectangles in the photo above started out as white clay, as shown by the circles of raw clay on top.

The first square on the left of each strip was baked for 30 minutes.  The second square was baked twice for 30 minutes each time.  The third square was baked three times for 30 minutes each time.  The rectangular base of each was baked four times for 30 minutes each time.  All were cooled between bakings.

Kato and Fimo Pro in the left column followed this same procedure, but were double-baked. This means the clay went into the oven twice for each square and the base: once for 30 minutes at 200˚, cooled and baked again for 10 minutes at 300˚ for Kato and 265˚ for Fimo.

The swatches were baked in two aluminum baking tins, one inverted as a lid and with two small ceramic tiles inside.  Each brand was baked at the manufacturer’s recommended temperature, verified by an oven thermometer.

RESULTS

Premo and Cernit stayed white, regardless of number of times baked.

Pardo Jewellery Clay grayed slightly the more it was baked. The changes are subtle.  It’s easiest to see the difference by comparing the square on the far left with the base.

Kato in the left column was double-baked and yellowed slightly the more it was baked.  This resulted in lighter-colored clay. Kato in the right column was baked normally and yellowed considerably more.

The official Kato website says, “…if you were baking a piece 3 different times, it’s recommended that you cure the piece for 10 minutes the first two times and 30 minutes for the final curing.” I’d add a note to be careful because the clay will be fragile when baked for only 10 minutes.

Fimo Pro in the left column was double-baked and turned a bit orangish the more it was baked.  It remained much lighter than the strip on the right.

Fimo Pro in the right column was baked normally and turned beige.  In this strip it’s most evident how the color can darken when baked multiple times.

Compared to the other strips in the left column, Soufflé turned the most yellow the more times it was baked. It would benefit from double-baking.

HOW RESISTANT TO BREAKAGE?

I had used a single drop of Kato Liquid Polyclay to stick the squares to the background.  The squares popped off easily from Kato, Premo and Soufflé.  With Fimo Pro, Cernit and Pardo Jewellery Clay I had to use my Xacto blade to literally saw them off.  They were fused to the background.

None of the backgrounds broke.  They had all been baked for two hours in 3o minute increments.

I tried only once to bend all the squares and the backgrounds so the ends touched.  That’s a really tight curve for 3/4″ squares.

Premo squares broke very easily.  Kato squares were extremely hard to bend but the double-baked ones did break. Cernit, Pardo Jewellery Clay, Fimo Pro and Soufflé were all flexible and didn’t break. I noticed small cracks starting in the squares of double-baked Fimo Pro, but not the background.

Thanks to Ginger Davis Allman for suggesting I try to break these, because it made a much better test.

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Results after bending each square and rectangle in half.

CONCLUSION

Premo and Cernit stayed the whitest. Pardo Jewellery Clay grayed a tiny bit. Kato, Fimo Pro and Soufflé turned yellow or beige the more times they were baked.  Double-baking helped Kato and Fimo Pro to remain lighter in color and would do the same for Soufflé.

I haven’t tested baking colored clay multiple times.  I imagine any darkening would be less noticeable.

Premo broke easily, except for the background which was baked for two hours in 3o minute increments.

Double-baked Kato broke with great difficulty.  Kato baked only once didn’t break and was very difficult to bend.

Cernit, Pardo Jewellery Clay, Fimo Pro and Soufflé were all flexible and didn’t break, but the squares of double-baked Fimo Pro had small cracks starting.

Kato Liquid Polyclay didn’t adhere well to Kato, Premo and Soufflé.  It adhered very well to Cernit, Pardo Jewellery Clay and Fimo Pro.

Double-baking gives a better appearance to Fimo and Kato, but sacrifices some strength unless baked longer.