Saturday, January 29, 2011
Portfolio Photography Cassius Basaltic Clay 4
Some things to keep in mind when using this clay.
1. When it starts to dry (before the leather hard state) just leave it alone. Do not add a slip at this time, the clay will obsorb the moisture from the slip and just fall apart. If you try to manipulate it, even by just a little amount the clay will crack.
2. When applying slip to the clay don't put it on to thick and put on the slip before it is leahter hard.
3. When bisqueing the clay, I would take it to Cone 04 and hold it at the temperature for at least 60 minutes for the gasses in the clay to offgas. Then once you go to do your final firing do it in an oxidation fire and only up to a max of cone 5. Otherwise the clay will start to bloat.
4. For a general all purpose glaze I would use my friends liner glaze (I will try and get the recipe from my friend Jamie Kirkpatrick) This glaze is great for a wide range or temperatures. Because of this the glaze stays in a molten (liquid state) from a low temperature. This lets any excess offgassing from the clays to get through and not cause any "moon" cratering in the glaze.
This is the glaze that was used on the inside of the cups above. I just left the outside of the cups with no finish, it is just the clay body itself.
I have another ceramic artist friend, Matt Allison, who uses the Cassius Basaltic clay as well. He will use a water downed version of a clear glaze as a finish on his pieces. But this is only after doing the long bisque as described above.
Also, from my research I have found that this clay after firing is food safe. There seems to be no manganese in the clay. But there are other black clays out there that have manganese in them, so be careful.