SOS, there are particles in my glaze!
Have you ever experienced this? You thoroughly stir a favorite dipping glaze before use and suddenly notice: "SOS, there are particles in my glaze!" Strange, because they certainly weren’t present when you first used the glaze. What are they? Where do they come from, and most importantly, how do you resolve this issue?
Not stones, but crystals
In some glazes, small particles can develop over time. These aren't actually real stones but crystallized components of the glaze. They can range in size from a few millimeters to several centimeters. Some are smooth and round, while others are rough and angular.
Water solubility
The crystals form due to partially water-soluble materials in the glaze, such as fluxing oxides like lithium oxide, sodium oxide, or calcium oxide. They come from ingredients such as:
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Nepheline syenite
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Some frits
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Sodium carbonate
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Lithium carbonate
Just because you use these materials in your glaze doesn’t mean you'll always get crystal formation in the suspension. Other ingredients may also cause crystal formation.
The conditions, both chemically and physically, need to be just right. For me, this usually occurs after a cold period in the studio and only in certain glazes. A glaze that is used frequently and in large quantities will experience fewer issues compared to a glaze that sits for a long time in varying temperatures.
Are those particles a problem?
It may seem a bit bothersome, but are these crystals really a problem?
The answer is simple: yes!
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The crystals stick as hard lumps to the glazed pieces and melt differently. This can result in unusual (but sometimes interesting) colors and patterns in the glaze.
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The composition of the glaze in the bucket is no longer the same. The crystals consist of (part of) the fluxing oxides, which means there is less of these in the glaze. Consequently, the glaze will behave differently in the kiln and is likely to melt less effectively.
How do you fix it?
So, how do you fix it? It’s simple: you need to dissolve them. Literally! The crystals are made of water-soluble materials, so you need to dissolve them in a small amount of water and then add the resulting solution back into the glaze suspension and stir.
Can't you just throw them away?
You should absolutely not simply discard the crystals. Doing so would mean throwing away important glaze materials and altering the recipe. As a result, the glaze will behave differently and might not melt properly. The color and even the texture could change as well.
Practical approach
1. Sift the glaze using a glaze sieve (60-100 mesh).
2. Scrape as many crystals as possible from the sieve.
3. Place all the crystals into a glass or a microwave-safe container.
4. Add just a small amount of water so that the crystals are barely covered.
5. Place the container with crystals in the microwave for a few minutes.
6. Repeat step 5 if not all crystals have dissolved; you may need to add a bit more water.
7. Add the liquid with the dissolved crystals back into the glaze and stir well.
8. Repeat these steps if crystals reappear after some time.
If you prefer not to heat glaze materials in the microwave, you can also add hot water to the crystals. This will require more patience, but the crystals will eventually dissolve with regular stirring.
Still have questions?
Do you still have questions after reading this article? Whether they’re about this topic or another clay/glaze/oven issue you’re facing, you can book a consultation with me online for 15, 30, or 60 minutes. Feel free to reach out!