Monday, January 1, 2018

Christmas and in between. Firing the wood fired kiln on New Year's Eve. Happy New Year!

It is just after 5 am. The world is waking up, a few birds are stirring. Outside my window darkness bleeds into the pre-dawn sky. Now the world has willow trees, and a purple sky that is covered with a blanket of cloud that moves steadily from West to East. It is disconcerting, the clouds make believe that the earth is turning, whilst they are stationary, like a fish swimming against the current!

Waikouaiti Old Post Office Gallery in early December.

Christmas
Our little gallery had a very slow start to December, but a genuine "Christmas rush" the week before Christmas. Thank Goodness!! We are so thankful to friends that made a special trip to the gallery and encouraged and cheered us, and to people that visited here for the first time.

We had our own Christmas Day a day early this year, driving through to my parents on Christmas Eve. We have to be somewhat flexible with these occasions, and it was better just to go when we were all feeling reasonably robust. We had a lovely time together, just the 4 of us this year, and it was good to enjoy each others company, some good conversation, and even a little music making. Dad and I played some Christmas carols together, he on violin and viola (not all at once!!), and me on the ukulele! I am sure that all of us were thinking of other family members too, near and far.

Mum, Dad, and myself at Christmas.

Back to Work
Laura and I were back to work on Boxing Day, with our gallery open again and me beginning glazing pots to go in the wood fired kiln. I have enough pots creating a "log jam" on my studio shelves for two or three more firings, but I also need to make a lot of small work to occupy the annoying spaces that inevitably occur in a kiln when you can fit 2 bowls on a kiln shelf, but not quite the three that you hoped would go there. Really pots are all the wrong shape, you have heard the expression "square pegs in a round hole", pots are the reverse problem... round pots in a square kiln!

Round pegs in square hole! Kiln loaded and awaiting firing.

Two days before New Year's Eve I spent all day loading the kiln and getting it ready to fire. I decided to use *wadding for most of the pots, to keep them from sticking to the kiln shelves. Wadding is something that potters who salt glaze their work will know all about, on the underside of most salt glazed pots you will see a characteristic set of marks that were the result of wadding. The wadding that I used was a blend of china clay, alumina hydrate, ball clay and grog with just enough water added to make a mixture that was very like bread dough in consistency. Wadding each pot made loading the kiln a slightly longer process, but it was oddly satisfying and enjoyable to be quietly rolling out little snakes of wadding in my fingers, nipping them off into even sized pellets of the doughy mixture, forming them into balls, wetting them, then placing them in a "fairy ring", for all the world like a circle of tiny mushrooms, on the underside of each pot!

We prepared firewood on the day before New Year's Eve, Laura did most of the wood splitting, as I did a couple of hours of final preparation on the kiln prior to its firing. Later I lit a small fire in the ash pit to dry the kiln and pots, and pre-warm the kiln.

I like firing the kiln in the **rain, and rain was forecast for New Year's Eve,firing day, so I extended the kiln shed roof with an old tarpaulin to give us some shelter.

Laura and the blue tarpaulin.


Firing on New Year's Eve
I lit the kiln at 5.30am. Rain was quite steady, but not particularly heavy. I settled into the rhythm of adding a couple of very small pieces of wood to the ash pit every few minutes, and Brian (Not our Cat!!!!) amused himself for a few minutes by climbing on the outside of the tarpaulin and pushing down at my head and shoulders with his front feet. The tarpaulin had more small holes in it already than stars in the sky, so I wasn't too sure how much cat climbing it would cope with, but Brian eventually discovered that it was wetter on top of the tarpaulin than beneath it, so came down and dried himself on my legs!

The rain went picka-pocka-plash, the birds began to sing, and trucks rumbled past on the main highway, tyres hissed on the wet road. The world slowly woke up as my little fire danced and flickered in the ash pit of the kiln.

Laura took over at half past 7, and I made some breakfast, then had a walk up the road to see if anywhere was open to buy some milk.

A grey and dripping day at 7.45am

At 8.30, with the kiln a shade over 300 Celsius (572 F), I took over stoking and started the gradual transition to building a fire in the main fire box. This involves keeping the ash pit fire going, but occasionally adding a small log at a time to the fire box. The temptation is to put too much in the firebox, and then have the kiln suddenly climb too rapidly, so patience is required.

9am and 385 on the clock (725 F).... a rhythm of regular light stoking of firebox and ash pit has been established, and the kiln is climbing at a brisk, but controllable 175 - 180 degrees (347 - 356 F) per hour, which we maintain on average until the last hour and a half of the firing.

10 am and 590 degrees (1094 F), Laura stokes. I need a rest, but am anxious about abandoning things altogether, as it will not be all that long before we have to think about reduction atmospheres and the like, so I don't want to go inside and fall asleep. I bring out a nice blue lounger chair, and fit it under the tarpaulin. I can rest on that, but still give directions if needed.

Brian making it difficult for me to read the kiln log!

11.15 and 820 degrees (1508 F) or so, time to push the chimney damper in a little and deliberately burn the wood somewhat inefficiently. Ideally, when making a ***reduction atmosphere, stoking and damper settings arrive at a balance where the kiln still can gain temperature, but the fire burns with a lazy, hazy flame. Every time new wood is added, oxygen is depleted from the kiln chamber, and smoke starts to issue from cracks around bricks and spy holes as the pressure builds in the kiln. It is easy to rush this stage when firing alone, to try to do too much. To choke fire box, to fiddle, to over stoke! With Laura feeding the fire, and me observing, it was easier to get things right, I could keep an eye on fire and smoke from the front of the chamber and call for "two more lumps of wood" at appropriate times, and Laura could watch for chimney smoke and let me know the colour, "black and thick", "brown", "grey", or "grey and thin", and so on! 

I made lunch at about 12.30, then took over stoking at 1am when Laura headed inside to open our gallery for the afternoon. The temperature was now indicating 1130 Celsius (2066 F). After half an hour I slowed the kiln's rise, so that there would be more time above 1200 degrees (2192 F) for time and temperature to work their magic with glazes. It would have been possible to have "spiked" up to temperature quickly, but I do not think that results from such firings are as good.

The ****cones that I had set to give an indication of temperature and heat work, started to bend from just before 2pm. On the top shelf, in the hottest part of the kiln, cone 10 was down at about 2.20pm. I continued stoking until 2.40pm, when cone 11 was half down on the top shelf, and cone 10 had a good droop on it in the middle of the kiln.

By 3.07pm I had the fire burned out and the kiln clammed up and the temperature down to just over 1000 degrees (1832 F).


And now we wait!
I will probably unload the kiln on Wednesday morning.

Happy New Year Everyone!


*Wadding
(From a recipe by Phil Rogers from his excellent Salt Glazing book.)
Alumina hydrate    2.0
China Clay             0.5
Ball Clay                0.25
Grog                      0.25

**Rain
Some potters believe (me included!) that moist air may actually improve the colours of the pots due to the extra hydrogen that is available as the extreme heat of the kiln splits off the H from H2O! This is not so far fetched an idea as it may seem, after all "water gas" was, and probably still is, manufactured by spraying steam over incandescent coke. This produces a potent blend of carbon monoxide and hydrogen that is a useful fuel. All air coming into my kiln is pre warmed over a bed of glowing charcoal, so humid air could well produce water gas.

***Reduction atmosphere
The kiln is fired with a surplus of fuel and an insufficiency of air. Oxygen is desperately sought, and even oxygen atoms that are part of the metals in the glazes are fair game! The result is that glazes change colour, copper green becomes copper red (or even lustred with a thin layer of copper metal), a honey coloured iron baring glaze becomes green, and so on. Even the colour of the clay that the pot is made of changes. Reduction atmospheres are one of the joys of firing with a fuel fired kiln, rather than an electric one.

****Cones
I have written about these elsewhere, but cones are made of a ceramic material that is similar to porcelain. These the cones are numbered and are made to bend over when their designed temperature is met. They are affected by temperature, and the time taken to get to that temperature. They measure "heat work".

17 comments:

gz said...

an exciting..if damp..day! Looking forward to seeing the results..Happy New Year!!

Peter said...

Lovely to hear from you Gwynneth, Happy New Year! :-)

Linda Starr said...

Happy New Year to you and Laura and the furry ones, we could use your kiln firing heat over here it is freezing almost all over the whole USA, more than usual, watching a pizza in the oven; will come back a bit later to read in depth your post. Oh a musical christmas, how wonderful, what are the fish on the wall, have I seen them before?

Linda Starr said...

Oh I hope you have a super firing, fingers crossed.

Peter said...

Hi Linda,
Happy New Year to you and Gary. I hope my kiln did not upset global temperatures too much, the butterfly flaps its wings in the Amazon and so on. Maybe when we heat up over here, you cool down in the USA to compensate! :-)

The fish on the wall are some beautiful ones that Laura painted, there are a some of them on a blog post I did on 20 November.

The kiln might be ready to open tomorrow afternoon. I'm a bit nervous about it as there is a commissioned piece in there, but we did our best and will just have to wait and see!

smartcat said...

WOW! You and Laura were far more industrious than we were. We zoned ou on a Game of Thrones marathon!

As Linda said we could use some of your heat here in the frozen north. It was -3 F. at 6:00 AM this morning.

Looking forward to firing results.

Happy New Year 🎈🎊🎆

Peter said...

Happy New Year Smartcat!

Lovely to hear from you. I just ran a conversion as to what -3 F is in C and I see that it works out at almost minus 20, which is frightening stuff! No need for a deep freeze to keep frozen meat, when you have the great outdoors giving you those temperatures! I hope that the Game of Thrones is sufficiently entertaining to keep you warm!

The kiln is at that frustrating point of cooling oh so sloooooowly, but still being a bit too hot to open. It is tempting to open a spy hole or two, but I've made the decision to leave it overnight and unpack tomorrow morning when all danger will have past! To avoid kiln opening temptation I have busied myself cleaning my studio and getting rid of some mediocre pots from the storage cupboard!

Melissa Rohrer said...

Christmas in short sleeves! The basement studio is frigid right now and I have not yet talked myself into going back to work. Interesting and informative notes on the kiln firing. And, Brian ( Not our Cat) seems quite comfortable.

Peter said...

Hi Melissa,
Yes, Christmas at a hot part of the year.. it has its advantages, but I fear that it lacks the special "something" of Christmas with snow! Brian is becoming an almost permanent resident here. Cats certainly know how to get their own way!

srgb said...

Hi Peter
Best wishes to you and yours for the new year.
Thanks for the post on my blog.
I am staggered at the amount of information under that black beanie you wear, you seem to rattle off all that information so easily you sure deserve all the sales you get, the shop looks wonderful so I hope it encourages people to buy and it is soon empty.
Seven weeks to me passing your door step so if time allows I will say hello on the day, I will be in Dunedin a few weeks so I will catch up with you at some time I hope. Bob

Peter said...

Hi Bob,
Good to hear from you. It would be great to catch up with you when you are in Dunedin, do keep in touch regards that and we will do our best to rendezvous!
My black beanie certainly is a good repository for information of certain sorts, but it is at least equally capable of forgetting more useful things, such as names, titles of books, where I parked the car, and what I did yesterday!
Happy New Year!

Arkansas Patti said...

Happy New Year Peter and Laura. May 2018 be a boon year. So good to hear from you and to see you are back posting. Interesting about the dampness and the color of the smoke. You sure need to know your science.
OK, after seeing Brian and you together, you are right. He is wooing you.

Peter said...

Lovely to hear from you Patti,
It always lifts my spirits seeing the little thumbnail photo of your smiling face in the comments! A Very Happy New Year to you too! It is nice to be wood firing again and to be posting on the blog a bit more often. Yes Brian is certainly trying his best to be part of the family here! That was the first time that he has used me as a chair, and it was a very special moment to have him climb aboard! He has a very sweet nature and was full of ecstatic purrs before he fell asleep!

Michèle Hastings said...

Happy New Year! I enjoyed reading about your firing day. It's always interesting to have a glimpse into other potters schedules. I hope your results were great and that you post them soon.

Peter said...

Happy New Year Michèle,
Good to hear from you. The firing was a successful one, but I'm still looking for an hour or two of sunshine in which I can see enough to take photos! NZ has been experiencing a "summer storm" for the last couple of days and most areas have been windy, raining and worse. We have escaped the wildest of the weather, but grey cloud has made things rather gloomy! Hope to post something soon!

Anna said...

A very busy Boxing Day! And congratulations on being listed on the Blog Review again for December. A very informative yet friendly post. Looking forward to seeing the results.
Happy New Year!

Peter said...

Hi Anna,
Lovely to hear from you. Happy New Year! Yes, quite busy here with the firing and so on. I managed to get some photos taken of the pots from the kiln so will put a post together later today all going well!