top of page

Salt Glazing: An Exciting Technique in the World of Ceramics

Writer's picture: Casper AndersenCasper Andersen

What is Salt Glazing?

Salt glazing is a chemical process used to create a glass-like layer on the surface of ceramic objects. The process involves introducing sodium chloride (salt) to the clay during firing, resulting in a chemical reaction between sodium and silicon. This reaction forms a glassy layer on the surface of the ceramics, which can have various colors and textures.

Salt glazing has been used for many years to create both artworks and functional items such as vases, bowls, and other types of ceramics. The process is known for its simplicity and flexibility, allowing adjustments to parameters such as temperature, time, and the amount of sodium to achieve different results.


Salt glaze vase



Chemistry and Physics of Salt Glazing

Salt glazing involves a chemical reaction between sodium and silicon. When sodium chloride is introduced to the clay during firing, gaseous sodium vapor is formed, which reacts with the silicon in the clay. This reaction creates a glassy layer on the ceramic surface composed of sodium silicate.

The chemical reaction is described by the equation:

2NaCl + SiO₂ → 2Na₂SiO₃ + Cl₂

This reaction is exothermic, meaning it releases heat, which helps melt the silicon in the clay and form the glassy layer.

The thermodynamics of the firing process are also critical. Firing temperature and duration can be adjusted to achieve different results. Higher temperatures and longer firing times result in a thicker, more glass-like layer, while lower temperatures and shorter durations produce a thinner, more porous layer.


Practical Application

Salt glazing is a practical process involving these steps:

  1. Preparing the clay: Ensure the clay is cleaned and dry before glazing.

  2. Adding sodium chloride: Sodium chloride is introduced during firing.

  3. Firing: Ceramics are fired in a kiln at a specific temperature for a specific duration.

  4. Cooling: The ceramics are slowly cooled after firing.

It is crucial to follow safety guidelines during the process, as it involves high temperatures and chemical substances. Protective gear such as gloves and goggles should always be used, and adequate ventilation is essential. Salt glazing is particularly hard on kilns and should not be performed in an electric kiln, as the heating elements can corrode (rust).


Variations in Salt Glazing

Salt glazing can vary based on the process and materials used. Common variations include:

  • Using alternative sodium sources: Sodium carbonate or sodium nitrate can be used instead of sodium chloride.

  • Combining with other techniques: Salt glazing can be paired with underglaze or overglaze decoration.

  • Using different clay types: Various clays, such as kaolin or feldspar, can be used for salt glazing.

These variations create differences in the color, texture, and properties of the resulting glassy layer.


Historical Use of Salt Glazing

Salt glazing has a long history, originating in ancient Egypt, where it was used to create ceramic objects with glossy surfaces.

During the medieval period in Europe, it became a popular method for creating both artistic and functional items such as vases and bowls. The process was valued for its simplicity and flexibility, allowing artisans to adjust temperature, time, and sodium amounts to achieve diverse results.

Today, salt glazing is still used to create unique ceramic artworks and functional items. Modern advancements, such as computer-controlled kilns, allow for greater precision and control during the process.


Environmental Impact of Salt Glazing

Salt glazing can have negative environmental impacts due to the use of chemical substances and high temperatures. Sodium chloride, if not handled properly, can pose risks to humans and animals. Proper safety measures and good ventilation are essential.

To mitigate the environmental impact, alternatives such as sodium carbonate or sodium nitrate, which are more environmentally friendly, can be used. Technologies like computer-controlled kilns can also optimize the firing process and minimize harmful emissions.


Conclusion

Salt glazing is a fascinating and creative method for producing unique ceramics. However, safety precautions and proper ventilation are essential to the process. With an understanding of its chemistry, variations, and environmental considerations, artisans can create stunning and functional ceramic pieces while minimizing risks and environmental impact.

A recommended video featuring a dedicated salt ceramist is an excellent resource for further inspiration.




2 views0 comments

Recent Posts

See All

Comentários


bottom of page