Atmospheric Clay Bodies

These are some clay bodies I mixed up and tested. They are designed to flash in soda and wood (atmospheric) firings.

Atmospheric Body 1

This is one of the first custom clay bodies I mixed from scratch. I didn't know what I was doing back then.

The body is supposed to be for Soda Firing. It has a Silica-Alumina Ratio of 2.77, designed for Alkali Flashing which may be a little low. However, I didn't choose the clays based on what color they might flash in soda firing. They were chosen just based on what I had lying around.

Material	Percent
Nepheline Syenite	30
Tile 6 Kaolin	15
Goldart	15
Helmer Kaolin	15
Optikast Kaolin	15
Hawthorne Bond	10
Sand (40 mesh?)	+3
Bentonite	+2

Low plasticity body. Optikast Kaolin provides no plasticity at all.

The Neph Sye content is probably higher than necessary. May do better at cone 6 than cone 10.

Sand is Ottawa Sand. I'm not sure what mesh it is exactly, but the particles feel uniform and around 40-50 mesh. It is undetectable when throwing and barely noticeable when trimming.

Atmospheric Body 2

Material	Percent
Nepheline Syenite	20
Tennessee 10 Ball Clay	65
Tile 6 Kaolin	15

A high alumina clay body for soda firing.

Extremely plastic due to the high ball clay content.
Throws and trims extremely smoothly.
Decently mature at cone 6, though I haven't done any measurements.

While this is probably a decent clay body, it doesn't justify the high time and energy investment in mixing. There are commercial clays like Laguna's B-Mix Wood which feel similar - it would be equivalent apply this recipe as a slip on white stoneware.

Atmospheric Body 3

Material	Percent
Nepheline Syenite	10
Helmer Kaolin	10
Tennessee 10 Ball Clay	30
Hawthorne Bond	10
Goldart	40
Mulcoa Grog 47-20x50	+3

I see the recipe as a combination of two clay bodies: - A mix of Goldart and Hawthorne, both which naturally mature at cone 10 - The specific proportion is up to personal preference - Hawthorne has a coarse grind and the iron speckles in the clays differ in size and quantity - A porcelaneous stoneware - This half is made of kaolin, white ball clay, and 20% neph sye for maturity - The lack of silica and proportion of kaolin is used to keep the alumina:silica ratio at 3 for soda flashing

Atmospheric Body 4

Material	Percent
Tennessee 10 Ball Clay	40
Goldart	20
Hawthorne Bond	15
Tile 6 Kaolin	5
Nepheline Syenite	10
Mulcoa Grog 47-20x50	10
Bentonite	+2
Sand	+1

Clay body designed for large vases in soda firing. Exceptional throwing properties due to that 10% grog. The downside is that it is absolutely hell on trimming tools.

Bellying out without a hand or rib on the outside produces very intense cracking patterns.

2.99 SiO2:Al2O3 ratio without sand and grog for flashing in soda firing
Hawthorne Bond added for iron speckles and small quartz grains
Goldart for additional iron speckles without larger mesh grains
As much Tennessee #10 Ball Clay as possible to increase plasticity without increasing the silica ratio (highest alumina content ball clay available to me)
A small amount of kaolin to target 3.0 SiO2:Al2O3 ratio
Some Neph Sye for maturity (Goldart and Hawthorne Bond are already fairly vitreous at cone 10, so not much is needed)
10% grog to make it easier to throw large without feeling grainy

Created 2023-09-23. Updated 2024-03-10.

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