Thixotropy and How to Gel a Ceramic Glaze

I will show you why thixotropy is so important. Glazes that you have never been able to suspend or apply evenly will work beautifully.

B. Glazes

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I will establish specific gravity first, then gel the slurry, then establish thixotropy. This will change your life! Glazes that you have never been able to suspend or apply evenly will work beautifully. Visit the links you see on this page to learn more. Understand the difference between specific gravity, viscosity and thixotropy. You will not believe what you see and how valuable this knowledge is!

The main question I get is how does one know what specific gravity to target for potters who are glazing bisque ware? Generally, start like this: Raw glaze (no frits) around 1.42. Partly fritted around 1.45. Alot of frit around 1.48. This should produce a slurry that is quite runny and ready to accept vinegar. Add it until you stir, stop and it continues in motion for 2 seconds and stops. If it is not runny then do not add any vinegar yet. Now put your hand or some other stirring implement into the slurry and extract it. When you do so the glaze should gel and hang on, covering it completely evenly. Only a couple of drips show fall off it. If it is not doing this, and the slurry is already viscous, you need to add water to enable gelling with vinegar. When it is right it should stop and bounce back slightly after two seconds. Repeat the process as needed. Be careful about how much vinegar you add so you do not turn it into jello. I like to have the specific gravity such that 3-4 capfuls of vinegar gels a gallon. If the slurry is too responsive to the vinegar, then the specific gravity is too high.

One more thing to keep in mind. I am talking about glazes that have enough clay in them to harden them well and suspend well. That means 15-25% kaolin or 10-20% ball clay. If your glaze has very little clay or it has a ton of clay, then you have a special case. This gelling process may still work, but it is better to reformulate the glaze, using glaze chemistry so it has the right amount of clay (there are videos and articles here on doing that). Gerstley Borate is a special case, it has the power of ball clay to suspend. If the glaze also contains clay in addition to the GB, then it is too high in plastic materials. GB gels glazes and turns them in a mess if there is 30% or more. Forget about using vinegar for these, you are more likely to need to do the opposite, deflocculate them. Seriously consider learning how to substitute the GB for Ulexite or a frit (there are videos and articles here on doing that too).

In Bound Links

  • (Glossary) Thixotropy

    Knowing about thixotropy enables you to mix non-gummed glazes that stay in suspension much better. They do not drip alot when a piece is draining. They go on evenly, of adequate thickness and do not run. They dry quickly (on porous bisque) and are just much nicer to use. The secret to all of this is...

  • (Glossary) Viscosity

    The term viscosity is used in ceramics most often to refer to the degree of fluidity of a slurry or suspension (the term 'shear' is often used when discussing viscosity, theoretically engineers understand viscosity in terms of layers particles or molecules that exhibit a friction that resists latera...

  • (Glossary) Specific gravity

    A comparison of the weights of equal volumes of a given liquid and water. Water has a specific gravity of 1.0. A ceramic slurry with a specific gravity of 1.8 is thus 1.8 times heavier than water. The best way to measure specific gravity is to weigh a container and record its weight, then weigh the ...

  • (Materials) Gerstley Borate - Plastic Calcium Borate

    Colemanite, Calcium Borate, Borocalcite

  • (Recipes) G2934 - Matte Glaze Base for Cone 6

    A base MgO matte glaze recipe fires to a hard utilitarian surface and has very good working properties. Blend in the glossy if it is too matte.

    2014-03-26 - A cone 6 boron-fluxed MgO matte developed at Plainsman Clays by Tony Hansen (a link below will take you to its page there). This page contains technic...

By Tony Hansen

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