What is it?
Glaze is the sometimes shiny, sometimes matte, outer coating on a piece of pottery. Glaze is what transforms the pottery into something non-porous, and therefore, food-safe. Glaze seals the pottery, so it is totally functional, and usually quite beautiful. Glaze can be the most transformative step in the pottery-making process.
Glaze is applied typically to bisque-ware (if you’re confused about what this means, check out my last post). Once the glaze is applied, the piece undergoes its last firing, and comes out of the kiln ready to be used.
- This is a before image of unglazed pottery, still unfinished. It is matte, porous, and not food safe.
2. Below is the after, glazed, finished pottery. There is color, sheen, and a ceramic barrier around the clay.
What is Glaze made of?
Glaze is made of four key components:
- Silica
- Alumina
- Flux
- Colorant
I’m not a scientist, so I will give a very brief description of each and why it is important in this process.
Silica (industrial sand) is the key ingredient in glass and ceramic glazes. It is essentially the glass-former in the glaze, which gives the glaze its sealant effect.
Alumina (or aluminum oxide) acts as the stiffening agent in the glaze. Without the alumina, the glaze would just slide right off the piece. Alumina essentially helps bond the glaze and the clay body.
Flux is the melting agent of the glaze; it helps lower the silica (glass) component’s melting point, so that it glazes the clay. Flux can be toxic and it is important that they are fired long enough to mature and be safe.
Lastly, colorant. As the name indicates, this is the color of the glaze. Silica is clear, and while I use a lot of clear glazes, other ceramicists use colorful glazes. The hard part about colorants is that they are typically quite different pre and post firing. It’s always a good idea to test a sample of glazes that you are unfamiliar with.
I’ll leave you with a new addition to the pottery world, Seth Rogan, and his colorful work:
Thanks for reading!
