|Monthly Tech-Tip |
Most people think that would be impossible. But it is not. This slurry will stay in suspension for days. How? It is flocculated using a tiny bit of powdered epsom salts. Without the epsom salts it is watery and will settle in seconds. How does the slurry apply to this porcelain? Since it contains no clay it has complete permeability. Against the immersed bisque a layer builds very rapidly, pieces must be dipped and removed immediately. Does it dry hard enough to handle? Yes.
These are pure Custer feldspar and Nepheline Syenite. The coverage is perfectly even on both. No drips. Yet no clay is present. The secret? Epsom salts. I slurried the two powders in water until the flow was like heavy cream. I added more water to thin and started adding the Epsom salts (powdered). After only a pinch or two, they both gelled. Then I added more water and more Epsom salts until they thickened again and gelled even better. They both applied beautifully to these porcelains. The gelled consistency prevented them from settling in seconds to a hard layer on the bucket bottom. Could you do this with pure silica? Yes! The lesson: If these will suspend by gelling with Epsom salts then any glaze will. You never need to tolerate settling or uneven coverage for single-layer dip-glazing again! Read the page "Thixotropy", it will change your life as a potter.
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.