Vitrify

Before we get to the yummy color tests, I did do a lab that explored the role alumni and silica play in the formation of glazes. Silica (SiO2) is the bedrock of ceramics. It's what forms the glass that makes the glazes but it's also what forms the glass needed to bind clay bodies, what makes clay bodies vitrified. Silica is abundant on the planet and you can find it in most materials that get mined. On a molecular level it's present even in the mineral clay we get from the ground. The ratio between the amount of molecular silica to molecular alumina ( Si : Al ) in any one glaze can make differences in performance and appearance. Trying to understand how these things affect my glazes means diving into chemistry which is a meaty subject and somewhat intimidating. I've tried again and again to understand how these elements work with incremental jumps in knowledge but nothing beats seeing things in concrete form like a test tile!

Strontium Chinese Bronze recipe with varying amounts of silica and alumina.

The results aren't staggering at first glance but you do notice a color shift as the Si : Al ratio changes.

Si : Al ratio can put your glaze on the map!

Altering this ratio can make a matte glaze glossy and vice versa. It can also help with problems like crazing. While crazing can look cool, on functional ware it can introduce weaknesses in the clay body which can cause the piece to fail eventually. Now, eventually may mean in a few months or a few years or a few decades depending on use and conditions but anything I can do to minimize this on my important functional pieces is worth doing, in my opinion. Sculptural pieces or things that won't get banged around as regularly as mugs, bowls and plates are less of a concern for me and the soda-fired work will probably always have some degree of surface crazing from the sodium that volatiles in the kiln. Like I said, this is about minimizing the problem or, conversely exploiting the effect.

Plotting the Si : Al ratio can tell me what zone my glaze is likely to fall on the map before I test it.

Tweaking the Si : Al ratio for crazing is something I have to do in conjunction with a specific clay body as the problem is not a glaze-only issue but a glaze-as-it-relates-to-the-clay-body issue. My increased knowledge here will help tremendously moving forward.