What are Bristol Glazes?

Bristol glazes are a type of glaze used on ceramics that can be fired at lower temperatures (around cone 6) compared to traditional glazes (cone 10). They achieve this by utilizing a specific chemical reaction between zinc and calcium.

How They Work

• Regular glazes rely on fluxes (like sodium or potassium) to lower the melting point of silica and alumina (the main components of glass).
• Bristol glazes use a unique combination of zinc and calcium to achieve a similar effect. This specific combination creates a “eutectic” reaction, where the mixture melts at a lower temperature than either zinc or calcium alone.

Benefits of Bristol Glazes

• Fired at lower temperatures, making them suitable for a wider range of clays.
• Relatively inexpensive compared to glazes relying on boron for lower firing temperatures.

Limitations of Bristol Glazes

• Colors may be less vibrant compared to traditional glazes due to the presence of zinc.

Sample Formula of a Bristol Glaze

• Cone 6 Bristol Glaze Example:
  • Nepheline Syenite 39.49%
  • Whiting/ calcium carbonate 16.01%
  • Zinc oxide 10.67%
  • EPK or kaolin 7.47% 
  • Flint/ silica/ quartz 19.81%
  • Cobalt carbonate 0.93%
  • Titanium dioxide 5.61%
  • Water 80%

Bristol glazes offer a valuable alternative for potters seeking lower firing temperatures. While they may have slightly muted colors, their functionality and affordability make them a popular choice.

You can learn more about Bristol Glazes on our YouTube channel.  Matt breaks down the Bristol glaze reaction that fires perfectly at cone 6—and shares it with you in our Cracking the Kiln segment – How do Bristol Glazes work?

Also check out For Flux Sake’s episode 78! to listen the gang talk about the chemistry that makes these glazes work.

Are you ready to take your glaze game to the next level? 

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-The CMW Team

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