Open fire

The weekend before last I helped Joe Morgan fire his wood kiln, and he very kindly made space for some of my work in the kiln. Last Sunday, after what seemed a painfully long wait, we opened up the kiln.

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Joe lifting the lid, underneath you can just see kiln fibre and kiln shelves covering the ware chambers.

The wood/soda firing process is very different from what I know. It took me a while to get my head around the approach required… using a different clay, glazing only the inside of pieces, using oxide slips to work with the soda to create the characteristic glaze that comes with soda firing. Even though all the pieces I made are essentially tests it was hard not to be very excited to find out how they had come out.

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Kitty and Joe Morgan lifting the final kiln shelves to reveal the pots inside.
You can see Joe’s amazing teapots and some of Hilary Firth’s plates and jars.

As we had thought the first stack had fired well, but the other two did not reach the required temperature. That said the firing was better than the previous one – it takes time to bed in a new kiln and Joe has plans to make a few modifications before the next firing.

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Some of the slip combinations and decoration I tried worked quite well, the glaze liner didn’t go as glassy as I had hoped, and I think I threw things too finely as many pieces warped. I’ve learned a lot and have lots of ideas to take forward. Now I just need to make some more pots.

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This carafe was right at the front by the fire box so it got very hot.
It also welded itself to the kiln shelf, but there are some beautiful colours here.
The inside and rim has a celadon glaze, but there was just bare clay on the outside.
This is where the soda and wood ash have created their own magic.
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This is perhaps my favorite piece from this firing, decorated in a copper/cobalt slip, with a celadon liner.
Where the soda has hit with full intensity it has created the strong blue glaze.
You can clearly see the other areas that received less soda.
These are more metallic in nature from the copper in the slip.

With huge thanks to Joe Morgan for such an amazing experience, and to Hilary Firth, Joseph Travis and Robin Palmer for such good company.

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Fire on

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Last weekend I had the great pleasure of helping Joe Morgan with the third firing of his new wood/soda kiln. I helped a little with its second firing at the end of last year.

Joe, Joseph Travis and Hilary Firth packed the kiln on the Saturday, then we fired on the Sunday. I arrived at 6.30am and the boys had already got going. I’m a novice at wood firing but I’ll try to explain a little of the process involved…

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The kiln is based on the ‘long’ kilns that Sandra Lockwood and Steve Harrison use in Australia. The fire box is of bourry box design, the chamber long and low. To start, a small fire is lit on the firebox floor using small pieces of kindling. It is imperative to slowly increase the temperature until the kiln has passed all the ‘danger’ points. Pour water at 100˚C, chemically combined water at around 350˚C and lastly quartz inversion at 573˚C. Over the next few hours the fire is built up increasing the embers in the ash pit until around 600˚C is reached on the pyrometer. At this point we switch from adding small pieces of wood through the front to much larger/longer pieces onto the upper part of the bourry box. These rest on hobs over the ash pit and allow the kiln to draw the heat and flames down through the kiln. The rate of draw and atmosphere can be adjusted by adjusting the primary and secondary air holes at the front of the kiln and dampers in the chimney. 

It is continual work to keep the fire fed… sawing, chopping and splitting wood to the right size; feeding and maintaining the fire; monitoring temperature and so on. It is intoxicating though – such a medieval process, involving proper graft, but massively exciting and hopefully rewarding. It is particularly enjoyable when with others… the chat and company spurs everyone on.

The temperature in the kiln’s chambers is checked firstly by using a pyrometer. In addition to this draw rings made from terracotta and stoneware are removed at various points to monitor the atmosphere in the kiln. Pyrometric cones are also observed through spy holes to check the progress in each of the ware chambers.

Once cone 10 goes down (1300˚C) in the first chamber (closest to the firebox) we introduce soda via bark ‘canoes’. These are carefully added to the firebox – the sizzle of the soda vaporising is a very welcome sound. The sodium vapour is then carried through the kiln with the flames and combines with silica in the clay. This will hopefully create the characteristic dimpled ‘orange peel’ glaze associated with soda firing. The last of the wood is added to the firebox before closing down the front of the kiln. Then side stoking begins through four small holes on either side of the kiln. These are located between the three ware chambers. Long, thin pieces of wood are carefully introduced to continue feeding the fire, all the while ensuring that they don’t touch the pots on either side. Finally more soda, wrapped in paper parcels are introduced through the four side stokes before the firing is completed.

By this time it was 9pm and we were exhilarated, but shattered. The firing was better than last time, but we won’t be sure of the results until we open up the kiln next weekend.

As we were tidying up in the darkness, we witnessed the perfect finale for our day’s labour… the most fantastic display of the Northern Lights. Breathtaking.

With many thanks to Joe Morgan, for help with the technical details.

Making of a mug: Day twelve

Part one
This was the view through the peephole this morning. The firing cycle had completed before I woke up and the kiln was already cooling. I then had to wait (not very patiently) until it got below 200˚c so that I could open it up. If you open the lid too early the rush of cold air can cause pieces to crack. So another couple of hours should do it…

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Part two
I opened the kiln about an hour ago… and this is what greeted me.

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Part three
So here it is… the finished mug.
Thank you for following me through its journey.

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Making of a mug: Day eleven

Part one

 

Part two
After dipping the mug was set aside to dry for a while. I check each piece thoroughly before putting it in the kiln. Often there are a few drips that need scraping off carefully with a knife (fettling). The bases are also given a final check and wiped if any glaze has stuck to the wax.

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Part three
Once again the mug is put into the kiln, this time for its glaze firing. With the biscuit firing it doesn’t matter if pieces touch each other, but with this firing it is very important that the mug has space around it. The mug will expand considerably as it heats up, and then shrink as it cools. If pieces are too close the glaze will cause them to stick together.

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Part four
Normally I would leave the mug overnight to dry before firing, but I’m trying to get the firing completed for the North East Open Studios (NEOS) which start on Saturday. To help dry it thoroughly I have added a preheat to the firing cycle. The mug will then be fired to cone 7 (1239˚c). This will take roughly 14 hours to reach temperature and once again a similar amount of time to cool. I hope to be able to open the kiln tomorrow night…

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This series of posts are also running on my Facebook page and Instagram feed. Apologies if you have already seen them there. If you would prefer to view them in one of these ways please click on the relevant icon in the right hand column.

Crack on

It’s been busy at the Cloud Pottery recently. I have three shows coming up over the summer so I’m trying to build up my stock. This means working mornings and evenings – whilst my littles aren’t around or awake. What this has reinforced is how much I love what I do. Sometimes I find myself thinking of it as a job, and panicking about how much I have to do… Then I get into the studio and settle quickly into a rythym: radio on, wedging and weighing out the day’s clay, throwing, turning yesterday’s pots and so on. Before I know it my ‘free’ time is up and I have to go back to motherhood. I find, particularly when I’m throwing, that I’m so absorbed that everything else just slips away. It’s not hard work, just a measured, thoughtful process that completely captivates me.

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I’ve managed to sneak in some new work… some plates and beakers that I had been hoping to make since last autumn. I’ve been experimenting with shapes for a while, here and there, and they will be refined as time goes on but I’m pleased with the results so far. The first plates have just come out of their glaze firing and hopefully the test beakers will be fired next week.

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Plates have been a new learning curve for me… I can throw wide based pieces fairly well, but I’ve been having persistent problems with cracking. After research it appeared that throwing on plaster might help, so I set about making some homemade batts and they have certainly slowed down the drying process. Originally I was concerned that pots would dry too fast as plaster draws out moisture from clay – in fact many potters use plaster tables to dry sloppy reclaimed clay to a workable consistency. On a wooden batt the rim of a piece can dry considerably faster that the base and starts to shrink putting pressure on the points where damp and dry clay meet. What I had overlooked was the way that plaster evens out the drying process by wicking away moisture from the base at the same speed as the rim allowing for even drying.

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The other possible cause of the cracking could be that my wider pieces all have turned, but entirely flat bases. During firing pots expand and then contract quite considerably. Friction against the kiln shelves can stop wider pieces from moving freely thus causing extra pressure on any weak points. To hopefully combat this my latest plates have been turned with twin footrings so that only a tiny proportion of the base is in contact with the kiln shelf. So far so good.

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So three weeks and two more sets of firings to squeeze in before Potfest Scotland in Perth. If you’re in the area please come along – it would be lovely to see you.

Open fire

During the open studios last week I did a couple of raku demonstrations using my homemade dustbin kiln and I had some lovely visitors to witness the process. Thank you to Hilary Firth from Starglazing for taking most of the following photographs…

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Kiln heating up nicely, using a probe to keep an eye on the temperature.

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Once the kiln reaches temperature and the glaze has matured,
the lid is removed and red hot pieces are removed with tongs.

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Red hot pieces are placed into a reduction (smoking) chamber lined with sawdust.
The lid is put on and the chamber is left until it has cooled.

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A blackened piece after being removed from the reduction chamber.

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The blackened pieces are then scrubbed under water.

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The best of the bunch with some great copper flashing.

The transformation the urchins undergo is fascinating to me. These blackened lumps are removed and are scrubbed until they reveal their true selves, just like treasure from a wreck being brought to the surface, cleaned and discovered,

Someone mentioned to me a while ago that I should try using less sawdust for the reduction and this advice worked a treat. In fact the results were the best ever. I’ve been trying to replicate one particular piece that I fired during my course at Gray’s and this was the first time I’ve managed that. So, after five raku firings I am by no means an expert, but progress is definitely being made.