Curing experiments part 1 | Cara Jane Polymer Clay Curing experiments part 1 | Cara Jane Polymer Clay

Curing experiments part 1

Posted on May 15, 2011

In order to find out how best to make strong bracelets I have a series of experiments planned. The first thing I wanted to find out was if polymer clay is stronger if it’s quenched, that is plunged into ice cold water straight from the oven. I’ve heard people say this makes it stronger, polish better and it will keep transparents more transparent. Well I’m using grey coloured scrap Kato clay so can’t comment on the transparency but my findings were that it doesn’t make clay stronger or polish better.

I wanted to know how strong polymer clay was when it was being bent so my clever engineer husband set up a test for me. I used to do similar work with composite materials for a living as a research materials scientist but I had big expensive machines and gauges to record what was happening (I’ve got a photo somewhere I will try and dig it out). My husband has also done similar work (we met at work) but is better at finding alternative ways to do things than I am, he’s a real problem solver!

Here is one of my extruded rod samples, of extremely well conditioned Kato scrap clay. They are 10cm long and about 6mm in diameter. I chose to extrude them so I could be sure they were as similar as possible.

The sample is ‘bridged’  over a gap. A loop of ribbon is passed over it and attached to an empty milk carton. Water is poured into the carton until the samples breaks and then we weighed how much water the sample had ‘held’. My husband tried to poor the water into the bottle at a steady rate, he isn’t holding the bottle just has his hand under it to catch it when the sample breaks so the water doesn’t spill. We weighed the water in the bottle at the point that each sample broke.

One of the test pieces not long before it broke! As you can see it has bent quite a bit.

All the test pieces were baked at 150°C (verified with oven thermometer) for 10 min. At this point
three samples were taken out of the oven and left on the side to cool, I am calling these samples ‘room temperature’. Three were plunged into ice water, I am calling these samples ‘quenched’ and three were left to cool in the oven which was turned off  and cooling down slowing, these are called ‘slow cool’ samples.

The results
‘Quenched’ samples breaking point weight – 485g, 673g, 772g
‘Room temperature’ breaking point weight -501g, 481g, 759g
‘Slow cool’ samples breaking point weight- 1069g, 1274g, 1522g

As you can see although there is a fair bit of variation in the results without a doubt the ‘slow cool’ samples were significantly stronger in flexure (being bent). Watching the test they obviously bent a lot more than the other 2 types of samples before snapping. I’ll try and video one of the next ones so you can see a test in action.

I then polished one part of each type of sample using my micromesh  cloths and counting the strokes, doing the same for each. The verdict on that is that there is no discernible difference in shine between them.

This test was with Kato clay, I am curious if it’s true for other polymer clays but being as I don’t use other brands I probably won’t take the time to find out I’m afraid.

I am going to do two more tests one to see how the baking temperature effects the strength in flexure (bending) and shine and one to see how the baking time effects the strength in flexure and shine. I am pretty sure that the longer baking time will make them more shiny when polished as that is one of the reasons I currently bake for longer, it will be interesting to find out in a more controlled way though.

The results may be a while coming so in the meantime I would advise that if you want your clay strong, leave  it to cool down in the oven after turning it off when you have finished baking!

7 Comments

  1. Wow! Do keep us posted on your very thorough experiments.

  2. This experiment was cool! Thanks for doing it and sharing the results. I will definitely start with letting pieces cool slowly. I had notice something but never went into making such a controlled experiment.

  3. You don’t mention what brand of clay you are using – some are significantly more flexible than others! I would be curious to know…
    So far, I have found Pardo to be the most flexible, but unfortunately, it is not ideal for the work I like to do, so…
    Great experiment with a significant difference in the results!

  4. sorry I can’t believe I missed out such a fundamental basic – it’s Kato – will update post. Thanks Cara

  5. What a fantastic experiment. Being fairly newish to clay this kind of information is invaluable, thanks for sharing.

  6. I’ve never used kato clay but I should think that the obvious difference in strength before breaking between the slow cool and room temperature/quenched samples is most likely due to the prolonged curing in the oven.

    Maybe it would make sense to cure all samples for 30 mins instead of 10 mins and repeating the test.

  7. I’ve done some more tests looking at the effects of curing times and temperatures, will try and publish the results this week but I’ve got a busy week – husbands 40th birthday!

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