|Monthly Tech-Tip |
I poured 4 teaspoons of two glazes onto a non-absorbent butcher’s board and let them sit for a minute, then inclined the board. The one on the right employs Gleason Ball clay, the left one has Old Hickory #5 ball clay. Neither has any rheology modifier additions. The one on the right has settled and, on incline of the board, the watery upper is running off. The other has gelled and the whole thing is running downward slowly. Below that you can see where I have begun to sponge them off, the one on the right is sticky. The most amazing thing about this: This difference appears despite the fact that there is only 7% ball clay in this heavily fritted recipe.
In ceramics, glazes are slurries. They consist of water and undissolved powders kept in suspension by clay particles. You have much more control over the properties than you might think.
No. 5 Ball Clay
No. 1 Glaze Ball Clay
A fine particled highly plastic secondary clay used mainly to impart plasticity to clay and porcelain bodies and to suspend glaze, slips and engobe slurries.
Glaze Slurry is Difficult to Use or Settling
Understanding glaze slurry rheology is the key to solving problems and creating a suspension that does not settle out, applies well, dries crack free.