My last two firings have been somewhat disappointing. There has been a lot of residual dry ash on and in the pots and it occurs to me that this problem might be solved if I had fired to a higher temperature to melt this ash. I looked at some of the remaining pots from my first firing again today and was really impressed with them. Whilst the first firing wasn't a resounding success by any measures, it did get up to temperature and those pots with an open top don't have that dusty dry ash sat in them.
I thought this thicker palette wood was effective, but now I am wondering if I would be better off with the thinner sweet chestnut strip-wood that predominated in the first firing. One good thing is that I've realised that I can fit longer lengths of wood in to the kiln than I thought at first, so less sawing. I don't know why I couldn't get up to temperature with the palette wood, perhaps I could have done if I'd stuck with it. In the end I had cone 10 bending in the front and cone 7 bending in the rear. That's not overly hot and about the same as the previous firing, whereas in the first firing I got cone 13 down in the front, so whilst I felt at the time that it was hard work achieving temperature it was clearly working.
Unexpectedly mild October weather allows me to sit in a T shirt and sieve my glazes and slips. I'm trying out a bunch of ball clays in combination with china clay - the different iron contents are supposed to yield varied results in a salt firing.These white buckets are great - what did we do before ebay?
I plan to fire again within 2 weeks, Friday 21st to be exact. That's the day before half-term and all my tutoring will be finished for a couple of weeks. I'm going to salt fire this time. I guess once I've done it I'll be salt firing for the next few times as the salt lines the kiln and effects the subsequent firings. I'm looking at stacking the back of the kiln with my regular glazes, blue, blush, tenmoku and putting some other pieces nearer the front that will get more of the salt. Also: - Ash glaze - a combination of local clay and local wood ash.- A basic slip made up of china clay in combination with a variety of ball clays. - A second slip as above plus nepheline syenite. Need to order a big bag of china clay tomorrow, seems like I have most of the other stuff. I'm thinking that I'll gain the effect of the salt and ash towards the front of the kiln near the firebox and that'll get really hot. Further back in the kiln where the temperatures are lower and the salt and ash less I'll rely on my usual glazes. This will mean getting the rear of the kiln up to at cone 9 (1257C) with the front hitting perhaps cone 11 (1293C). There is always some difference in the front and rear temperatures. I'm going to reposition the pyrometer to read at the top of the kiln which will free up two ports, rear and middle through which I can view cones and extract test rings.
My second attempt at firing the wood kiln was both better and worse. Safe in the knowledge that I could reach temperature I allowed the process of firing to be far more relaxed. I got up early and began a small fire under the grate around 6am, stoking every 20 minutes or so. By 9ish I was firing on the grate. The pallet wood burned nicely. I closed the flue around 900C to get more pressure in the kiln and to attempt to achieve more reduction in the clay body. This causes more flame and smoke as the fire seeks oxygen from wherever it can be obtained, including the clay itself. Opening the flue at 1000C the temperature climbed rapidly. I soaked for a while at cone 9, trying to keep Orton cone 10 up. I'm not sure it was hot enough - there is a wide variation of temperature in this kiln and I'm happy to accommodate that, but I was measuring in the hottest place. I fired the kiln down to 950 with small sticks, finally getting to bed around 3am. On opening the kiln a few days latter I found the work to be somewhat bland. The ash had been minimal, perhaps a product of pallet wood, which, good as a fuel is somewhat lacking in fly-ash I'm led to understand. The main concern however was the black dust that had settled on the pots. On a hunch that it was iron I tested it with a magnet and sure enough it was iron, either from the grate or from the nails in the pallet wood. Further research seems to indicate the latter. Not too big a problem - I'll just take care to avoid wood with nails in the future. I'm not working on creating pots for another firing in October. I'm planning on using salt and wood in the next firing. I love the effects that some people get with their wood firing, but I just don't have the capacity to fire for the 3+ days that such a firing requires. I have done some salt and soda firing in the past and loved it, and I recall Mick Casson telling me that he thought the combination of wood and salt to be the ultimate ceramic surface, and if it was good enough for him then it should be more than enough for me.
Here are the pots that I took to Buckingham Old Gaol today.
I'm taking some pots along to Buckingham's Old Gaol today - more to follow.
All the pots are in my living room at present. Its a big job sorting through them. Used to be I only had to think about clay and glaze with an electric kiln, now I have to think about the position the piece is placed within the kiln.
That brown pot in the middle right, the one with the hole in, that hole was burned out in the firing, along with the eroded front. It's a mix of local clay and porcelain and didn't work out too well.
Nice view along the top of the kiln here. The castable keystone (grey strip at top of kiln) shed a few bits of debris I reckon, hopefully that won't happen too much in future. See the blue cup, the ash really makes the blue run.
One or two nice pieces above, The reddish flashing on the two bottom right I like. The nearest piece, bottom right, has a lovely velvety surface. Its one of my standard glazes which has come out really different. On porcelain if flushes to a purply yuck (lower floor, 3rd from left) but on white stoneware and the other stoneware clays it becomes a soft grey.
Above: good view of the pyrometric cones here. Middle set are Orton 10, 11, 12 - hardly touched. The set to the left are some old stock, I can't remember the make, a symbol on them looks a bit like the infinity symbol or a looped knot. They were cones 7,8,9,10, and even 10 has gone over pretty well. Above: The blues come out better nearer the back of the kiln, requiring less ash. This is my standard blue glaze that you can see on other pots on this site, but comes out quite different in this kiln to the usual electric kiln. The method of stacking bowls didn't work out too well for me. I only used 3 wads and this wasn't enough. The porcelain warped, but luckily I left the top rim unglazed and was able to separate these two - actually I quite like the shape they've ended up as, slightly triangular. When I've sorted them out I'll try to take some better photos of the best pieces. Going to need the grinder to remove some of the wads.
Emptied the kiln yesterday morning with the help of Frank. Its a mixed bag as I expected, but there are quite a number of nice pieces so overall I'm pleased with how it went. Its evident form the pyrometric cones that there was a big temperature difference from the front to the back. Orton cone 12 was flat at the front so that was around 1315C. At the rear 10 was just beginning to bend, perhaps 1265C. I don't really have a problem with that, I can use that to my advantage placing different clays and glazes in different parts of the kiln. One thing I realise I did wrong is evident from the dry unmelted ash that has collected in some pieces which must have blown in to the cold pots. This has left some pieces with an unpleasant gritty surface in places. On the last stoke I should have closed up the air intakes under the grate - with these open and the kiln cooling, cool ash was sucked through on to the cooling work. Will know better next time. Much of the work shows evidence of a strong kiln draft throughout the firing; a strong line of melted ash on one narrow face. Hopefully playing with the passive dampers will spread this a little more next time. The silicon carbide shelves stood up well. The wadding isn't coming off too readily in places, but I think will come off with a little work.
That place up the side definitely didn't like the heat and warped really badly.
I'm not sure how much reduction I achieved. I need to review the glazes. I just let the kiln do its thing and didn't try to 'do' anything apart from stoke it. I figured that if I tried things out on the first firing and the results were good I wouldn't know if it was because of things I'd done or not. So this firing presents a baseline against which to measure future changes.
Took a snapshot through the stokehole this morning - around 200C on the pyro. I'd made the dish on the right fairly thick, thinking it might help it take being stood on its side, but that didn't work out too well. I'm guessing the problem was cracking through being heated too fast early on. Same with that pair of dishes at the top there; I had one stacked upside down on the other. That little pot at the bottom front on its side, I don't know where that came from but it looks nice - hope I can get it out, probably stuck down fast.
The first firing is done. Cone 12 went down, indicating a temperature in excess of 1300C. From what I could see I think this was a bit much for some of the clays I'd used, which have warped and cracked. It was a full day, started at 6am and finished about 9pm, so 15 hours firing. Still at 500C today, so I'll see how it is tomorrow. Chances are I won't unpack it until Sunday.
Smoky!
A distant shot of the kiln taken by my daughter on a walk with her friends. Progress.
Warming up. Door all bricked up.
That's bright - the googles, they do something. Stoking.
Evening action.
Short fast flame.
Yep, that's hot. A view into the kiln through the stoking hole. Around 1300C in there.
Cooling down. Still pretty hot though!
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