| Monthly Tech-Tip | No tracking! No ads! |
Pyrax (Pyrophillite) is a mineral having a very low thermal expansion. It stands to reason that if we can maximize its percentage in a body and not fire the body to a point that changes the crystal structure, it will be resistant to thermal-shock cracking. To that end, I mixed it with only kaolin (ball clay would add some quartz that would increase thermal expansion). I made slip-cast pieces of similar thickness for testing. I fired them to cone 2 (after finding that by cone 4, shock-resistance begins to decline). As you can see from the video, the addition of grog actually harms the performance! The higher the Pyrax, the better. To get a real appreciation for how well this body endures differential heat stress, wait till the end to see how a glazed porcelain piece compares.
| Materials |
Pyrophyllite
A refractory aluminum silicate mineral often used in clay body recipes to lower thermal expansion, control fired maturity, mullite development catalyst, etc. |
| Glossary |
Thermal shock
When sudden changes in temperature cause dimensional changes ceramics often fail because of their brittle nature. Yet some ceramics are highly resistant. |
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