I recently did a bit of experimentation with (NM Clay Co) mica clay to try and answer some questions that have floated around.
What is safe, and importantly - effective, for firing mica clay at DMS? My answer is still broadly ‘Not over cone 04’, which is our bisque firing. However, we did notice a distinct difference between cone 010 and cone 04, so doing a special firing is occasionally worth the effort. At the much lower temperature of cone 010, the mica flakes were bigger and more distinct at the edges. At cone 04 you are definitely starting to see the mica melting leaving smaller specks. This is proving hard to photo (by casual, lazy phone photography at my kitchen table) but it is noticeable in person. @Liam has some pics of the white mica that shows a bit better.
This is where I say STOP, consider this strongly before attempting! At cone 6, our glaze firings, the clay maintains nearly all of its structural integrity. No real slumping, blistering, cracking, etc. However, it does begin to melt a little and will definitely stick to whatever it is on. All the mica, of course, melts and the clay goes a nice dark red. Interesting surface gloss as well. If you absolutely had to fire to 6, you could try doing so in a dish of alumina to prevent sticking.
That said, it doesn’t really make sense to pay more for mica to then just disappear away said mica! Stick to bisque 04 and you will be okay. Remember to leave a note with anything that is outside of the ‘norm’ to help those that do all the groovy loading. For those loading: if you see a glittery mica piece on the glaze shelf, it WILL fuse hard to whatever it touches. I’d put it on the Needs Attention shelf unless it is on alumina/sand/something that’s not just a cookie.
Additional Important Tidbit:
Not all mica clays are the same! The only type we’ve fired/had in the space has been from NM Clay…that I’m aware of. I’ve not seen anyone bring any in outside of our events/class. (Someone could absolutely mix mica into a super low fire clay and make a stunning amount of mess.) The cool, full lava melt, cautionary tale of KnowYourClayBody! piece we use in Ceramics 100 was almost certainly not mica.
Cone 010
Cone 04
Cone 6
