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Making Pots

Loading Pots

Firing Kiln

Unloading Pots

Report

Making Pots - February 2012

Zig Zag Bowls

Fairly large bowls, with impressed comb decorations. Glazed internally, but left to pick up the reduced ash toasting outside.

The lower bowl is a teaser / taster of the fired bowls, showing that exterior toasting.

A collection of amphora vessels.

Made in two parts. These have been biscuit fired and will be glazed inside and down the top rim and neck. They will go into the wood kiln on their sides, resting on scallop shells.

The bottom image shows a pair of these fired, having picked up a dusting of wood ash and a dose of heavy reduction.

Loading Pots 6th & 8th March 2012

There are no images of loading the kiln this time, because the camera battery was flat!

Firing Kiln -9th/10th March 2012

The gentle preheat begins!

Note that the firebox has been deepened by removing the layer of bricks and replacing them with kiln shelves. The iron grid has been modified by welding bars along the bottom, to reduce the size of gaps so that the burning fuel stays suspended longer.

The single brick baffles the entry to the firebox, so the lower door can be opened to allow more air in, without too much of it going straight over the grid.

The chimney has be modified by increasing the height of twin-walled stainless steel flues, now ther are two tall flues, instead of the three shorter ones used on the first firing.

Laurence's cat's cradle of ropes helps to steady the flues, but luckily it did not get too windy before they were dismantled after the firing.

The overnight pre-heat went very well, drying out the raw pots at about 200C, needing a large elm log every hour and a half or so, with a couple of smaller branches to provide some flames now and then.

Laurence casting doubts about the power of the standby ventilator, rigged up to deliver a bit more air into the firebox, a cheap electrical extract fan with a bit of flexible hose and an aluminium pipe into the bottom of the firebox.

During the day various stoking regimes were tried out to see what was effective and efficient at raising the temperature.

Getting to a thousand C was not too much of a problem, but it became obvious that 1250C was going to be another struggle, with not enough updraught being created by the revised chimney system.

The ventilator tube could be positioned anywhere, or just pointed at the firemouth.

As the firing progressed into the evening, it became apparent that more air was needed, so Luke's garden vacuum was wheeled out and connected to the flexible hoses.

Slowly the temperature was pushed up by exerting a positive pressure into the fireboxes, forcing air in to help burn the timber, which was a mixture of split elm and pine floorboards and pallet wood.

The blown air input resulted in flames escaping from the fireboxes when opened before the pressure has died a bit.

Potatoes were baked on the chimney tunnel!

Laurence took turns pointing the blown air at the firebox to encourage better burning.

Slowly the temperature continued to rise. The fireboxes were intensely hot by midnight!

The pressurised kiln chamber encouraged some leakage from the loose bricks of the kiln door, so flames sometimes leapt up and emerged between gaps in the ceramic fibre insulation panels. The smokiness of these flames also showed that the fuel was not being burnt completely, resulting in reduction inside the kiln.

Normally a negative pressure inside the kiln would suck air into gaps.

The dark cold moon looked down through the trees at the glowing kiln.

The cones seen through the spy-hole looked as if they were almost starting to bend, certainly the very bright light looked close to 1250C.

The stoking was stopped at 1am on Sunday morning, a quick clean burn was followed by a rapid cooling to abotu 1100C, then the kiln was clamped up to cool more slowly.

The potatoes were forgotten about in all the excitement and got a bit over-done! Perhaps they should not have been glowing red when removed from their cooking place!

Unloading Pots - Tuesday 13th March 2012

Next morning the door panel damage was inspected, the aluminium foil was burnt away where the flames had escaped. The ceramic fibre was OK.

The first peek in the top of the chamber as the top layers of bricks were taken down from the door.

The cones - 8 & 9 - 1250C are still upright.

The pots are heavily reduced, as expected and desired.

Some glazes are mature, some still too matt.

The full frontal view, after the door bricks had been removed.

The pots are a varied collection of heavily reduced and toasted vessels.

The only cone to really show any bend was at the back above where the flames entered the chamber.

The corners seemed not to have got so hot - perhaps they were packed too densely and the shelves were too tight against the kiln walls to allow the passage of heat.

The top left of the chamber.

Dave Emery's jugs were so very close to being matured, but the insides were still slightly matt.

The back of the kiln seemed a bit better fired, the beakers were all nicely glazed - although in the second firing that Cornish Stone glaze will not need quite so high a temperature to melt.

The bowls of all sizes and jugs all looked OK, with some splendid bits of ash induced speckling.

All the amphora vessels were a success, with a range of ash effects and glaze melts.

The shells left very authentic scars on the clay and kept the pots from sticking to the shelves.

The smaller jugs picked up some good deposits of ash on the shoulders, producing some delightful mottled colours.

Many of the larger bowls were also good, with subtle variations in colur and texture.

The beakers were very nicely finished, the unglazed surfaces shone through the reduced texture, with the impressed comb decoration being picked out very well.

The smaller bowls also picked up some very attractive earthy ash markings.

Report and Conclusions

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This firing was more successful than the first, but still not quite hot enough. Heavy reduction produces some beautiful earthy tones, but comes at the price of burning more fuel.

The various routines tried out with stoking fuel at different rates were not conclusive. The daytime stoker Dave Emery did not believe that the elm was producing enough heat quickly to do much heating up, but Bill in the early evening used split elm mixed with some pine to reach 1100C without too much effort, by keeping the fires well stoked and burning fiercely. The beds of embers were producing a huge amount of energy to get newly introduced wood ignited quickly. The late night crew used a mixture, but kept to thinner pieces to reach 1240C ?

The redesigned firebox bases and iron grids worked much better.

The twin chimneys were not producing enough updraught, although as the temperature increased that that did improve somewhat. They were not handling a high enough volume of air to draw into the kiln and get the fires burning properly.

The back up blower provided more air, but not very controllably and with a positive pressure in the kiln which is not really a good thing.

The longer stoking time certainly helped to increase the glaze maturity.

The third firing is being planned for early May 2012, before which the aim is to dismantle the existing chimney completely and rebuild it completely in brick.

The next batch of pots will follow the same themes, with Bill's wares inspired by prehistoric shapes and decorations. Several other potters are beginning to get interested in submitting their own vessels to the flames, now they have seen some more results.

Comments are very welcome - email Bill Crumbleholme

Thanks to :-

Dave Emergy

Alistair Hampson

Laurence Eastwood (even if he did go off partying for most of the day, but he was there when the heat was building up!)

Luke & Martin - who seem to enjoy fire more than is natural! They also come up with good suggestions and solutions.

Steve and Joe for their long distance encouragement and suggestions.

John for supplying the shells.