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Making Pots

Loading Pots

Firing Kiln

Unloading Pots

Report

Making Pots - March - April 2016

Pots just thrown, drying out ready to turn the bases and then raw glaze.

Loading Pots 2016

Back of kiln chamber loaded

Front of kiln loaded

Firing Kiln - 16th April 2016

7am - a beautiful start to the day, after a night of gentle pre-heating, stoking every hour.

Temperature kept below 200C until 4am, to dry out kiln structure, shelves and pots.

7am firebox being stoked up a bit quicker, from 400C to 1000C by noon

The afternoon crew - Jennie Hanrahan - inspecting the digital thermometer readout = 1040C at top of chamber and 790C at bottom.

While Steve Pallant builds up his calorie intake ready for work!

Jennie stoking

Steve stoking

Jennie stoking, with a bit of flame blow-back.

The Pallet battens are stacked around the chimney to help dry them out and also insulate the chimney a bit.

Bill checking the cones through the spy-hole, about 4pm. Top reading 1125C, bottom 960C, so a while to go!

This shows the small gap between the vertical kiln shelves that can close off the chimney when slid in. The glowing flames can be seen travelling through, the intensity of the flames varies in a cycle as the wood is put in the fire boxes and starts to burn.

Jennie came up with the strategy to watch this and instruct the stokers to only stoke when the flames started to die. That avoided overstoking and a more efficient, cleaner burn, with less reduction.

Between 6pm and 8.30pm we burnt old roofing batten from a local church (thanks Simon!) which was a brilliant fuel - very well seasoned; dry and just the right size. The temperature increase was the highest ever during this period of firing, rising 100C in an hour and a half.

This is the lower part of the fire box at 6pm, showing a build up of embers on the middle shelf, with ash below.

The embers are "riddled" with an iron bar now and then, to stir them up and make them fall through the gaps, allowing a cleaner burn and for air to get into the depths of the fire box and kiln chamber.

The night shift crew and catering division!

Lottie was not allowed to use the axe! But actually because all that work had already been done.

7.30pm. Richard stoking - the kiln had got to over 1200C.

Because the firing was quicker than usual, the cones did not go over at the normal digital reading of 1220C (there is a 40C error in calibration), because the amount of "heat effort" was not as great as with a slower firing.

So from here on the aim is to keep the temperature as high as possible and "soak" the pots, so the glazes mature completely. It also helps the temperature increase lower down the chamber, which is cooler to start with. The convection currents do not reach the bottom corners, but infra-red radiation does eventually.

Bill stoking at 8.30pm

The 2nd batch of battens have been removed from round the chimney and are stacked ready to use.

The roofing batten ran out and these battens were used, but the temperature went up and down between a reading of 1220C and 1180C

Bill tried fanning the flames in the firebox - to force a bit more air in, but it did not help that much, for the effort involved.

Along the top of the kiln chamber the flames escaped more than usual, because Bill did not finish off the bricking-up as well as he should have and also the ceramic fibre blanket normally placed over it had fallen apart.

The flames show a positive pressure inside the chamber, as the wood is introduced and initially produces a surge of gases as the wood is turned to charcoal. The chimney is not pulling enough to create a negative pressure.

Richard using up the last of the roofing battens at about 8.45pm

Bill stoking by the light of the moon (and a couple of strong electric floodlights!)

The flames come out of the top of the chimney at the really hot times!

Bill tried throwing spade-fulls of charcoal into the firebox - having heard it might be useful. The charcoal was low grade small pieces, slightly damp, so probably didn't do much good!

9.30pm. Steve still stoking up.

Lottie took over stoking from 11pm until just past midnight.

She tried a careful strategy of stoking both fireboxes one after the other and then leaving them until the temperature had risen and then started to fall again. This enabled her to get back up to 1215C.

We left the kiln without stoking to oxidise for a while - which is meant to help clean up the surfaces and brighten the glaze shine.

Then the kiln was left for half an hour with the firebox doors open, to crash cool it down to 1100C and it was then blocked up, the chimney shut off and the dampers removed to stop the draw.

Unloading Pots - 18th April 2016

The front of the chamber after taking down the brick door, revealing the fired pottery.

Looking OK! Most of the pyrometric cones have gone well over - showing the temperature was easily hot enough.

Close up of front lower section.

The small nuggets are Virginia's clay beads.

There was the usual cooler spot in the lower corner away from where the flames enter the kiln chamber - that cone is still upright and the pots are lighter coloured with less reduction.

Close up of the top of the front .

There is a stack of plates in the middle.

Back contents of the kiln chamber revealed when the front stack has been removed.

Close up of lower section of back.

Close up of upper back of chamber.

A collection of Bill's vessels unloaded.

The front pots are for fermenting cabbage - the top has a trough in the rim which is filled with water into which the lid sits, thus forming an airlock - allowing the fermentation gases to escape, but the bugs cannot get in.

The same pots and a few more rearranged and from the other end of the table.

The "mortaria" bowls have a much more melted glaze than previous firings - the Light Oatmeal glaze has melted more and run, with the ash helping to flux it and create very pleasing streaks.

Bill looking pleased, if a bit sleep deprived!

Some of Jennie Hanrahan's bowls, with a selection of splendid glaze effects.

Steve Pallant's pots, shame about the blue!

Richard Gould's pots, splendid bowls. Don't mention the tea pot handle!

Bill's classes Pots, featuring Caroline Sharp's urchins.

Class pots, featuring Jo Hamilton's large jar.

Class pots, featuring Birgit's bowls.

Dale's butter dishes and spoons.

Dale's mugs

More of Dale's mugs.

Report and Conclusions

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Maybe the highest temperature yet reached in all the firings to date? Certainly the cones were well gone and the glazes very mature.

But very few broken pots, a couple of cracked ones and a couple with small bloated bulges.

The light oatmeal glaze was more melted than usual. The reduction was high, with darker than usual surfaces which were also shinier.

Some of the pots near the entry points of the flames were very well toasted, with glaze runs stained green with ash.

Many thanks to the loading and unloading crew and especially the stokers. Both Steve and Lottie became more proficient at getting the rythym going to keep the temperature rising. Jennie's idea to watch the flames entering the chimney worked well as an indicator of when to stoke.

Many thanks Simon and Cliff and the Hope Church for a supply of old roofing battens - an excellent fuel for the later stages of firing.

Thanks to to Buildrite for letting us have a stack of pallets.

It was great to see some new faces at the kiln site, helping with the tasks.

Comments are very welcome - email Bill Crumbleholme

Thanks to :-

Simon & Cliff and Hope Church for the roofing batten timber.

Buildrite for the pallets.

The Landlord and sons for support and encouragement.

Pottery Class members and Jennie Hanrahan and her class for help filling the kiln and firing it.