A glaze is a vitreous substance fused on to the surface of pottery, by dipping, spraying or brushing, to form a safe, sealed coating in the bisque-fired wares in order to make it waterproof and food safe. Glazing enhances the fired clay piece both on a functional and aesthetic level. Not only does it make pottery safer, by sealing the clay bodies, but also gives it life with any colour or pattern you wish to create. Glazing makes the simplest ceramic ware into a work of art.
When it comes to glazing the possibilities are infinite. There are endless colours, patterns and techniques that you can create with glazes. Since glazes are made of chemicals and compounds, each of them reacts differently with the various clays. The beauty of this is that every piece, whether artisanal or industrially made, will be completely unique.
Types of glazes
Ceramic glazes can be classified in various ways. However, if we use temperature as the baseline they can be classified as either low-fire, mid-fire or high-fire.
Low-fire glazes are fired at 1845 degrees Fahrenheit. Low-fire glazes are great for when you have a very specific, controlled design in mind. The resulting colours can be bright and predictable and do not melt together much.
Mid-fire glazes are fired at 2192 degrees Fahrenheit. The colours tend to have more variation and melt together to create more romantic visual effects.
High-fire glazes are fired at 2305 degrees Fahrenheit, creating a strong and vitreous ceramic. The colour range tends to be more limited.
Process of glazing ceramics
1º Mix the glazes with water
Glazes are essentially made up of three ingredients: glass-formers, fluxes, and stabilizers. Depending on the type of glazes there will be different proportions of these three ingredients.
In a bowl mix the glazes with water, keeping attention on the consistency and texture of the mixture.
2º Applying the glazes to the bisque-ware by dipping, spraying or brushing
Depending on the effect wanted, the glazes can be applied by dipping, spraying or brushing.
Before applying it to the bisque-ware it’s important to clean the bisque-ware in order to remove all dust before starting, and to mix the glazes as well as possible. When glazes are left to settle in a bucket the heavier sediments sink to the bottom, so it is important to mix the glaze properly, before dipping the ceramic ware, to ensure a smooth, even consistency.
3º Glaze firing
The ceramic body is loaded into the kiln for the glaze firing. The kiln is slowly brought up to the right temperature for the sílica in the glaze to melt, then slowly cooled again.
This makes the ceramic body solid and strong, waterproof and food safe.
Test glazing is a laborious but necessary process of ceramic manufacturing. Given all the endless ways different glazes can react with different clays, it’s important to know what you’re getting. Once your ceramics have gone through the glaze firing, the process will be irreversible.
Test glazing is the time to explore different colours together, different techniques and different patterns. Record everything you do so that you can recreate it when it’s time to glaze the finished work.