Epsom who?
Epsom salts, or magnesium sulphate, are commonly used as bath salts. They are said to help relieve muscle and joint pain when added to a bath. They also have laxative properties, although I would not recommend drinking them. Epsom salts are sometimes referred to as bitter salts, and that name is very well deserved.
Epsom salts are an inexpensive and highly effective flocculant. A flocculant is a thickening agent. You can compare it to cornstarch in a sauce.
Epsom salts act on the clay particles in a glaze. These clay particles, originating from materials such as kaolin or ball clay, are attracted to one another when Epsom salts are added. As a result, they form a network of clay particles that helps keep the other glaze ingredients suspended. This improves suspension and prevents the glaze from forming a hard layer at the bottom of the bucket. It also makes glazing easier. The glaze provides good coverage and flows out beautifully.
When to use Epsom salts
You only need to use Epsom salts when necessary. The following glaze characteristics can give a clue:
- the glaze is extemely thin and you didn't add too much water
- the glaze dries very fast
- the glaze hardpans by forming a hard cake at the bottom of the bucket
How to prepare Epsom salts
Epsom zout koop je (bv. in de webshop) in de vorm van kristallen. Je moet deze kristallen oplossen maar niet zomaar. Je maakt een gesatureerde oplossing van epsom zout. Ik leg je graag uit hoe je dat doet.
Equipment
Prepare this:
- small container with a well fitting lid
- Epsom salts, at least 100 g
- hot tap water
Process
Weigh out 100 g of Epsom salts, or a multiple thereof, into a container. Add 75 g of hot water, or a multiple thereof, and stir well. The water will dissolve the crystals, but not completely. In fact, 75 g of water is not enough to dissolve all the crystals, and that is exactly what you want. A solution that is not fully dissolved is called a saturated solution. Put the lid on the container and clearly label both the container and the lid. Based on my tests so far, Epsom salts have an unlimited shelf life.
How to use the solution?
Add the liquid, not the crystals at the bottom, to the glaze. I prefer using a syringe so I can keep track of exactly how many millilitres I have added.
Hoeveel je moet gebruiken hangt helemaal af van het glazuur in kwestie. Sommige glazuren hebben slechts een kleine hoeveelheid (minder dan 1 ml nodig op 1kg glazuurpoeder) en sommige vereisen meer.
Start slow
Always start with just a few drops. Stir the glaze thoroughly after each addition. You will notice the glaze gradually becoming thicker. Be careful not to make the glaze too thick. A thick glaze produces different results from a thin glaze.
Should I always add it?
No. In glazes that contain little or no clay, such as many crystalline glazes, Epsom salts will not work. Epsom salts act on the clay particles in a glaze. If there are no clay particles present, nothing will happen.
Other glazes are naturally already highly flocculated. They are fairly thick and creamy without the addition of any additives. In that case, there is obviously no need to add Epsom salts. Doing so would only make the glaze thicker and difficult to work with. In fact, you may need to do the opposite and deflocculate the glaze instead. You can learn more about this in my workshop “Glaze Consistency, Viscosity and Specific Gravity.”
Want to know more?
Epsom salts are one part of the equation, but achieving consistent glaze results involves much more than that. In my workshop “Glaze Consistency, Viscosity and Specific Gravity”, I take a deeper dive into topics such as flocculation and deflocculation, specific gravity, viscosity and thixotropy. It comes highly recommended for anyone who mixes and uses powdered glazes and occasionally runs into problems in the studio.