See the magic of thixotropy as I mix a 20kg batch of G2926B glaze

I mixed 20kg of glaze powder into 20kg of water, turned out super watery. Yet the specific gravity was 1.46, too high. How? But, IInstead of more water, I added Epsom salts—and boom: A perfect thixotropic gel. It glides on smooth, no drips, no thickness issues.

In this video, I mix 20kg of glaze powder into 20kg of water using our powerful propeller mixer. The resulting slurry is like water, absolutely unusable. Yet on measuring the specific gravity (using a hydrometer because it floats freely) I find that it is too high, I actually have to add more water! How is that even possible? Instead, I add Epsom salts and mix again and the slurry gels and hangs on in a perfectly even layer when I dip the spatula. This is a thixotropic gel, it will apply evenly to bisque ware yet not go on too thickly. We normally recommend a specific gravity of 1.44 for this glaze, but in this case, it seemed watery enough at 1.46 (on use, it will become clear if 1.46 is OK e.g. if it goes onto the ware too thick). If that happens I'll just add water to 1.44 (and more Epson salts if needed). Based on online pricing at this time, coverage is minimum six times and as much as twenty times less expensive than buying jars of transparent brushing glaze (considering both the total powder weight and the specific gravity difference between this and commercial glazes we use).

Links

Materials	Epsom Salts
Glossary	Thixotropy Thixotropy is a property of ceramic slurries of high water content. Thixotropic suspensions flow when moving but gel after sitting (for a few moments more depending on application). This phenomenon is helpful in getting even, drip-free glaze coverage.

Pure feldspar applied as a glaze: Possible because of the magic of thixotropy.

This picture has its own page with more detail, click here to see it.

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 then 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. The result is a thixotropic slurry. 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!

See the magic of thixotropy as I mix a 20kg batch of G2926B glaze

This picture has its own page with more detail, click here to see it.

In this video (see link below), I mix 20kg of glaze powder into 20kg of water using our powerful propeller mixer. The resulting slurry is like water, absolutely unusable. Yet on measuring the specific gravity (using a hydrometer because it floats freely) I find that it is too high, more water is needed - how is that even possible? Instead, I add Epsom salts and mix again and the slurry gels and hangs on in a perfectly even layer when I dip the spatula. This is a thixotropic gel, it will apply evenly to bisque ware yet not go on too thickly. We normally recommend a specific gravity of 1.44 for this glaze, but in this case, it seemed watery enough at 1.46 (on use, it will become clear if 1.46 is OK e.g. if it goes onto the ware too thick). If that happens I'll just add water to 1.44 (and more Epson salts if needed). Based on online pricing at this time, coverage is minimum six times and as much as twenty times less expensive than buying jars of transparent brushing glaze (considering both the total powder weight and the specific gravity difference between this and commercial glazes we use).

By Tony Hansen
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