Ian Currie Memorial Lecture with Renton Bishopric

Renton Bishopric, an industry veteran of over 20 years, encourages ceramicists to develop an understanding of how glaze materials behave in order to develop their own uniquely identifiable glaze style. Developing your own glaze style, and communicating the story of inspiration with your audience, is key to creating work which engages your audience.

Glaze knowledge is best developed by building from the work developed by talented predecessors such as Ian Currie, Greg Daly, Janet de Boos, and Harry Memmott.

In summary, the five main categories of glaze materials are:

1.Glass former: silica, 1710C melting point;

2.Bonding agent: alumina, kaolin, ball clay, 2040C melting point;

3.Primary flux: (fluxes lower the melting point): potash feldspar or soda feldspar;

4.Secondary flux: calcia, or magnesia, boron, zinc, lithium*, lead*, baria*, frits. (*not suitable for tableware);

5.Colourants: oxides or stains.

There are many benefits to using stains as a colourant for glaze: stains hold colour well; they are available in a wide variety of colours; may be mixed to create new colours; and have reliable results. Potters should be aware that some stains may act as a flux.

While developing a personal glaze style it is essential to have a methodical approach to producing glaze samples and recording results. This includes having a clean space and tools, appropriate storage and labelling, systematic approach to creating glaze tests, and documenting the results.

To start, make a batch of blank test tiles. Renton creates test tiles by using rolled clay which is cut into strips and small wells pressed into the clay. These are then bisque fired. Next, create a glaze using a known and reliable base, in a small quantity (at least 100g) and then produce a simple line blend, where the colourant percentage is varied. Ideally these are created in sets of two: one for oxidation and one for reduction. Methodically label each one and record the results, including the log from the firing. It is essential to develop a coding system for test tiles and consistently use it.

Creating a sustainable long-term practice relies on creating a safe working environment and being mindful of waste from both in terms of the environmental and cost. At his business, Pottery for the Planet, glaze leftovers are recycled to create new limited-edition glazes.

Renton advised that it’s best practice to be respectful of using knowledge of others and acknowledge your sources. You are under no obligation to share your information however, in his experience, some of the best results have come from collaboration with other potters.

Photo and text by Stephanie Henricks. This article was first published in the Ceramic Arts Queensland Quarterly Bulletin November 2022.