# Preparing Work for Salt and Soda and Reading the Results

Unit: Alternative Firing Methods
Topic: Salt & Soda Firing
URL: https://claybook.studio/learn/preparing-work-for-salt-and-soda-and-reading-the-results/

# Designing for Atmospheric Glazing

Because the glaze develops from the kiln atmosphere rather than from applied glaze, the preparation and design of work for salt and soda firing is different from standard glazing.

## Slips Are Essential

Salt and soda on bare clay produce a thin, often pale result. To get rich colour and depth, potters apply **slips** before the first bisque firing. The slip interacts with the atmospheric sodium to create denser, more varied surfaces.

*   Iron-rich slips produce warm ambers, oranges, and browns.
*   Cobalt slips produce deep blues with the atmospheric glaze over them.
*   White kaolin slips produce clean, crisp surfaces that the salt or soda glaze coats clearly.

## The Orange Peel Texture

The signature orange peel texture of salt and soda glazing is caused by the sodium vapour depositing unevenly on the surface. The level of texture can be influenced by:

*   Clay body texture: rougher surfaces produce more pronounced orange peel.
*   Kiln placement: areas near the ports where sodium is introduced receive heavier deposition.
*   Number of salt or soda applications: multiple smaller additions create more even coverage than one large addition.

## Kiln Wear

Salt and soda slowly destroy kiln bricks over time because the sodium reacts with the silica in the brickwork, just as it does with the pots. Salt kilns are typically built with hard, dense bricks and are dedicated specifically to salt firing: you cannot use a salt kiln for standard oxidation or glaze firings without contaminating your work.

## Explore More

The dedicated kilns required for salt and soda firing are lined with dense [refractory brick](https://en.wikipedia.org/wiki/Fire_brick) to resist the corrosive effects of sodium vapour. [Bernard Leach](https://en.wikipedia.org/wiki/Bernard_Leach) was instrumental in promoting salt glazing for studio use in the 20th century, and the technique was later introduced into American university ceramics programs, where it remains a valued part of the curriculum.

## Reading Results More Accurately

*   Check surfaces at multiple angles in natural light; orange-peel depth can be subtle.
*   Compare port-facing and sheltered sides of the same form to understand deposition gradients.
*   Note where slip thickness amplified colour so you can repeat successful prep.

## Pro Tip

Log sodium introduction timing and amount by minute. Atmospheric glaze quality improves dramatically when additions are consistent, not improvised.

## Check your understanding

### Question 1: Why are slips important in salt and soda firing?

- [ ] A. Slips prevent the sodium from reacting with the clay body
- [x] B. Slips provide a richer surface for sodium to react with, producing deeper colour and coverage
- [ ] C. Slips protect the clay body from being damaged by the salt atmosphere
- [ ] D. Slips are only decorative and do not affect the salt glaze result

Tip: Salt and soda on bare clay alone produces a thin, pale result. Slips provide a richer surface for the atmospheric sodium to react with, creating deeper, more varied colour and better glaze coverage.

### Question 2: Why are salt kilns dedicated solely to salt firing and not used for standard glaze firings?

- [ ] A. Salt kilns reach lower maximum temperatures than standard kilns
- [x] B. Residual sodium in the kiln walls contaminates standard firings with unwanted atmospheric effects
- [ ] C. The thick kiln wash required for salt firing prevents standard glazes from melting properly
- [ ] D. Salt kilns are identical to standard kilns: the same kiln can be used for both without issue

Tip: Sodium from salt firing reacts with and gradually erodes the silica in the kiln brickwork. More importantly, residual sodium vapour deposited in the kiln walls will contaminate any subsequent standard firings, producing unwanted atmospheric surface effects on pots not intended for atmospheric glazing.

### Question 3: A pot has strong texture on one side but weak deposition on the opposite side. What does this most likely indicate?

- [ ] A. The glaze slurry was too thick across the entire pot
- [x] B. Directional sodium flow and kiln position created uneven atmospheric deposition
- [ ] C. The clay body partially vitrified on only one side
- [ ] D. This can only happen if the kiln was under-fired by one cone

Tip: This pattern usually reflects position relative to sodium entry and kiln flow paths. Atmospheric deposition is directional, so port-facing surfaces often receive heavier sodium exposure.