The 3-4 main groups of substances in glazes
What do the ingredients actually contribute to the glaze?
Here is some information about the substances found in the raw materials you buy. That is, a bit about what is in feldspar, what is in kaolin, and so on.
You can certainly mix glazes systematically without this knowledge, but having a little understanding helps. You will get that knowledge here.
Traditionally, the substances in the glaze are divided into three groups.
Glass. The basis of glaze is glass, and the basis of glass is quartz. This is what our common white beach sand in Denmark consists of.
Stabilizers. Ordinary glass is not very suitable for glazes but can be used for special effects.
Therefore, there is aluminum in the glaze, which makes the glaze more viscous and not just runny. Boron acts as a stabilizer too
Flux. These are substances that make the glaze melt at a lower temperature. Without these substances, the glaze would only melt at a temperature where the clay is already melted.
Flux can be divided into two groups, depending on the temperature at which they work.
Low-flux. These work at all temperatures, both earthenware and stoneware.
High-flux. These only act as flux at stoneware temperatures.
There are thus four groups in total if one distinguishes between the two types of flux.
| 1. Low-flux | 2. high-flux | 3. stabilizors | 4. glass (silicium) |
| Li – Lithium Na – Sodium K – Potassium B – Boron | Mg – Magnesium Ca – Calcium Sr – Strontium | B – Bor Al – Aluminium | Si – Silicium |
Those who have some knowledge of chemistry can see that it corresponds to the main groups in the periodic table. But don’t worry, you don’t need any knowledge of that to learn about mixing glazes.
A small curious detail. Boron, which is a stabilizer, also acts as a low-flux. For example, in raku glazes.
Based on this, raku glazes are divided into two groups.
- Boron glazes that are fluxed by boron, and
- Alkali glazes that are fluxed by sodium and potassium.
An overview of the contents of the different raw materials
The different raw materials contain one or more of these four groups of substances.
Quartz contains only glass.
Chalk contains only high flux.
Kaolin contains both silicon/glass and stabilizers.
Feldspar contains silicon, aluminum, and sodium/potassium.
Since feldspar contains so many components, it is usually used as the base for glazes. Then kaolin, chalk, and quartz are added in that order when testing and calculating glazes.
A chart like this can be made to show what they contain:
| material | 1. Low-flux | 2. High-flux | 3. Stabilizor | 4. Glass |
| Feldspar Nep. Syen. | Na, K | Al | Si | |
| Kaolin Ball Clay | Al | Si | ||
| Whiting | Ca | |||
| Dolomite | Ca, Mg | |||
| quartz | Si |
But aware. It is not easy reasing
A conclusion from this is that the same glaze can be made using different raw materials. In other words, you may find a recipe for which you don’t have the ingredients, but you can create another recipe that results in the same composition. However, this is not easy to figure out on your own and is best done with the help of a program like glazy.org.
Another use of this knowledge is that you can modify a glaze to give it different properties. For example, by replacing kaolin with ball clay, you can create a glaze that is easier to brush on.
More about these properties here: Basic Properties of Ceramic Glazes.