Here's how to use Epsom salt
You bought a SOGO glaze at Colpaert and see that Epsom salt needs to be added? No idea what that is? Don’t worry, I'll explain it in this article. Using Epsom salt is actually very easy and, on top of that, it's extremely cheap.
Epsom what?
Epsom salt, or magnesium sulfate, is essentially just bath salt. It’s said to relieve joint and muscle pain when added to your bath. It also has laxative properties, but I wouldn't recommend drinking it. Epsom salt is also known as "bitter salt," and that name is VERY apt.
Epsom salt is an inexpensive and highly effective flocculant. A flocculant is a thickener, similar to how cornstarch thickens a sauce.
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Epsom salt acts on the clay particles in a glaze. These clay particles, such as those from kaolin or ball clay, are attracted to each other when Epsom salt is added. This attraction forms a network of clay particles, allowing other components in the glaze to remain suspended. As a result, everything stays better in suspension and the glaze does not form a hard crust at the bottom of the container. This also makes glazing easier, as the glaze provides good coverage and flows smoothly.
When do you need to use Epsom salt?
You should only use Epsom salt if it's necessary. The following glaze characteristics might be an indication:
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The glaze is very thin and you haven't added too much water.
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The glaze dries extremely quickly when applying it to a piece.
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There’s a hardpanned glaze layer stuck to the bottom of the bucket that’s hard to redistribute.
How do you prepare Epsom salt for use?
You can buy Epsom salt (for example, at Colpaert) in crystal form. You need to dissolve these crystals, but not just any way. You need to make a saturated solution of Epsom salt. I'd be happy to explain how to do that.
Supplies needed
Here's what you need to prepare:
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A small container with a tight-fitting lid (e.g., a 500ml yogurt pot)
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Epsom salt, at least 100 grams
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Hot tap water
Working method
Weigh out 100 grams (or a multiple thereof) into the container. Add 75 grams (or a multiple thereof) of hot water and stir well. The water will dissolve the crystals but not completely. 75 grams of water is not enough to dissolve all the crystals, which is exactly what you want. A solution that is not completely dissolved is called a saturated solution. Put the lid on your container and clearly label both the container and the lid with what’s inside. In my tests so far, Epsom salt remains indefinitely usable and will not go bad.
How should I use Epsom salt?
Add the liquid (not the crystals at the bottom) to the glaze. I prefer using a small syringe so I can keep track of how many milliliters I'm adding.
The amount you need to use depends entirely on the glaze in question. Some glazes only require a small amount (less than 1 ml per 1 kg of glaze powder), while others require more. For SOGO glazes, the amount needed is indicated on the label.
Always start cautious
Always start cautiously with just a few drops. Stir the glaze thoroughly after adding it. You'll notice that the glaze gradually begins to thicken. Make sure your glaze doesn’t get too thick! A thick glaze will give different results compared to a thin glaze.
Should I always use epsom salt?
No! In glazes without or with very few clay particles (e.g., crystalline glazes), Epsom salt won’t work. It specifically acts on the clay particles, so if they aren’t present, nothing will happen.
Other glazes are naturally highly flocculated. They are already quite thick and creamy without the addition of an additive. In such cases, you should not use Epsom salt. It would only make the glaze thicker and more difficult to work with. On the contrary, you might need to do the opposite and deflocculate the glaze. More about that in my workshop "Glaze Consistency, Viscosity, and Specific Gravity.
Want to know more?
Epsom salt is one thing, but achieving consistent glaze results involves much more. I offer an engaging workshop on the topic "Glaze Consistency, Viscosity, and Specific Gravity," where I explain in detail about flocculation and deflocculation, specific gravity, viscosity, and thixotropy. It’s highly recommended if you make and/or use powder glazes and have encountered issues in your studio!