Upwey Potters Soda Firing

Last revised: 9th April 2013.

The Upwey Potters are a group of ceramic artists who live & work in Upwey, Dorset, England, making and selling their work and running Workshops.

This page gives an overview of the process of Soda Firing with images and text.

Ceramic Review Issue 205 Jan/Feb 2004 featured an article by the Upwey Potters on the building of their kiln.

Follow the links below to see images from some firings :-

Firing Number One Firing Number Five Firing Number Eight
Firing Number Nine Firing Number Ten Firing Number Eleven
Firing Number Twelve Firing Number Sixteen Firing Number Seventeen
Firing Number Eighteen Firing Number Twenty Firing Numbers
Twenty-eight and Thirty
Firing Number Thirty-one Firing Number Thirty-eight  

Some of Bill Crumbleholme's Soda Fired Beakers

Take a look at the pages with images and details of RAKU firing.

This page gives details and images of the soda kiln constructed and first fired by the Upwey Potters in June 2001. These notes explain how the kiln works.

Front view of the kiln.

The "hot face" is High Temperature Insulating Bricks

Then a layer of Carbo-wool - second generation ceramic fibre.

Then a wrap of aluminium foil.

Then an outer skin of light-weight furnace bricks.

Clay slurry was used to hold the bricks in place.

Base formed by hollow concrete blocks


Side view of rear of kiln, showing rear burner, base of chimney with damper (marked with graduations to guide insertion.)


The shape is a catenary arch.

The curve was formed by suspending a chain from two points and marking on a board.

A temporary timber former was made over which the HTI bricks were laid. The former was removed and the arch is left self-supporting.

The door is made of HTI bricks, cut to fill the space. Each brick has Roman Numerals carved on it to record position. Some are removable to enable the soda to be injected, the cones viewed and the rings pulled.

"Isometric view" of kiln showing the two butane gas burner positions, which point along each side in opposite directions.

The heat from the flames rises up to the top of the arch and then down through the firing chamber past the pottery and through slits in the lowest shelf and then out through the back of the base and into the brick chimney. rising past the damper up to the top of the bricks. A metal flue is positioned on top of the chimney when firing to provide up-draught. A section of the corrugated tin roof is slid forward to allow the metal flue up.

The kiln takes about 10 hours to reach 1250 degrees (using pre-biscuited pottery), with an hour soak at 950.

Specially formulated ceramic cones are placed in line with the upper spy-hole brick, they slump to indicate when the correct amount of heat has been applied.

Soda (Agricultural strength Sodium bi-carbonate) is dissolved in boiling water and then put in a garden pressure spray. The solution is sprayed in bursts of 20 seconds through the various port-holes and over the flame of the front burner. It vaporises immediately and is drawn through the firing chamber.

The soda vapour comes into contact with the pottery and reacts with the surface to form a glaze. The amount of reaction is dependant on the silica content of the body and the quantity of soda.

The vapour is distributed fairly evenly through the kiln and covers the inside hot face of the arch. Resisting wash is painted on all the shelves and props. The pottery is placed on tabs of solid resisting material.

The pottery tends to be attacked more by the soda where close to where it is injected.

To check if enough soda has been injected, rings are pulled from the kiln at intervals and their state noted.

Fil Cooke is shown here performing the necessary juggling act.

The soda is injected over a period of 2 hours, with the gas adjusted to keep the temperature steady.

This ring shows a reasonably even coating of soda.

We use 4lbs of soda, half a pound at a time in one and a half litres of water (don't you just love partial metrification!)

The kiln is fast cooled down to 900 deg, then all the holes are bunged up and the damper closed. These are opened again at 200 deg,

20 hours after the gas is turned off the kiln is cool enough to open. The bricks are carefully removed and the gasps of "ooohh look at that beautiful effect" etc begin!

The kiln will comfortably hold a couple of dozen assorted pieces (about 30 lbs in weight)

These pots by Bill Crumbleholme were thrown in coarse stoneware clay and combed to provide a textural context for the soda to enhance. They were biscuit fired in the first slow kiln drying out firing. Oxided slips were banded round them and a glaze poured into the vessels (the soda does not reach inside enclosed shapes).


Pat March made a collection of small test pieces, known as pasties.
Another of Bill's bowls shows intense soda activity where it was close to the side of the kiln in contact with the rising flames.

This small vase was tucked away and was more evenly coated by the soda.

Note the resistant pads, prop and kiln wall.

A test platter gives an indication of the effect of using various slips, some of which enhance the soda effect and some resist it.
One of Fil's multi-fired test pots.
Irene Passmore's dish shows areas of various coatings.

The Upwey Potters are very pleased with this venture and look forward to producing a selection of attractive pieces for sale at their exhibitions.

Please contact Fil Cooke for more information.



Go to Beaker Folk Pottery (Bill Crumbleholme's)

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