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Is Terracotta Stronger Than A Bisque Fired Stoneware?


Edee415

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I am wanting to make some essential oil diffusers, and I've noticed that most of them are made from terracotta clay so that it can absorb the oil.  I was wondering if I could use a bisque fired mid-fire stoneware clay, bisque fired to a cone 04 instead, or would it be too fragile?  I put a few drops of essential oil on a bisque fired piece of cone 5 b-mix and it worked beautifully, but will it break easily compared to an unglazed terracotta?

 

If terracotta is stronger than a bisque fired b-mix, what temp would I fire it to?

 

Thanks!

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there are so many different clay bodies this question is almost impossible to answer. on something that small, strength should not be too much of an issue. iron bearing clays tend to mature  at lower temps than non iron bearing ones, so you do find nice strong red clays at lower temps , however if you like the cone 5 b mix and it seems OK, use it..if it is too absorbent or seems a little punky at cone 04, try firing it to cone 02 or 01

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Diffusers can come apart with the uneven heating-especially low fire ones.I was in that business at one time (for 10 years and made many thousands) and the company that contracted us wanted pots that did not crack over time.High fire porcelain glazed was the best solution for them liability wise as that never cracked or broke.

My guess is the terra-cotta ones will come apart over time unless they are vitrified. Whatever clay you use make sure its fired to its vitrification point . I do not think absorbing the oil is a good thing.

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  • 2 weeks later...

I made many many oil lamps in the 70-80's. Even with glaze inside ^10 R stoneware the lamp oil seeped through the bases and onto tabletops. My friend, boss and mentor, Rita Singleton Bullis, learned/figured out a solution. We painted the bases with white glue, slightly thinned with water, applied with a stiff, short-bristled brush. It dries clear and a bit glossy, doesn't wash off (unless soaked, I guess). I think the Elmers-type glue is milk-based and the casein seals against teensy oil molecules. I agree with MarkC, a porous clay will retain old odors or stale oil smells, you'd have to refire the pot to get rid of it.

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