The different kinds of materials

An simplified way of looking at materials is that they are all just baskets of oxides, with each material bringing various oxides to the mix. This is what Mixup's oxide analysis shows. But keep in mind that it is a simplification.

In the real world materials are of course more complex. They have different melting properties depending on their molecular structure and how they are ground and processed. Many materials have trace amounts of oxides that don't show up in the official analysis. Most materials that are directly mined from the ground vary a bit. Manufacturers have various strategies to try and keep a material consistent, but many materials drift in analysis over time.

For this reason glaze analysis is approximate, and often works best as a comparison tool. If you know how an existing glaze fires in your kiln then analysis is often a great way of creating a similar glaze or changing the glaze you have.

Broadly speaking pottery materials break down into these categories:

• clays
• feldspars
• silica
• frits
• fluxes
• additives

Clays and feldspars are mined and often come and go over the years depending on the size of the deposit. Both clay and feldspar are composed mostly of silica and alumina. Feldspars are often characterized by an alkaline flux component, so you commonly see soda feldspars, potash feldspars and lithia feldspars, indicating the primary flux in the mineral.

Silica used to be provided by mined flint, which contained small amounts of other oxides, but now is a fairly pure product. Mixup has a material called "Actual Flint" if that is really what is called for, but often when a recipe calls for "Flint" it is best to add "Silica".

Most of the time potters prefer a non-soluble mineral. Having a material dissolve in water leads to uneven application. However some oxides, like boron, are difficult to find in a non-soluble form.

A frit is a manufactured material that is previously molten glass that is cooled and powdered. Frits have good melting properties and are a great source of oxides like boron that are difficult to find otherwise in non-soluble form.

Fluxes can be provided in many mineral forms. Dolomite for example provides calcia and magnesia together. Wollastonite provides calcia and silica.

Additives are many and varied, ranging from metallic oxides like copper oxide used for coloring, to CMC gum, an additive that improves how a glaze goes on the pot but completely burns off in the kiln.

Next: Using Mixup