Wednesday, May 16, 2012

Firing once a week keeps you warm and cheerful!

A hat, a jacket, two jerseys, and other layers just about kept me warm stoking the kiln!
We had another wood firing, exactly one week after the one before, and the kiln was opened yesterday morning.  I started the firing on a chilly morning at 5.30am, with a gusty wind hissing through the trees and showering leaves and acorns.  It was cloudy, and rain seemed close, but never quite arrived, and I had two brief glimpses of a moon that seemed to be surfacing and drowning in dark pools of night sky. I had two more large planters to fire, and a few smaller pieces that did not matter so much.  Whilst it was rather hard on the aging potter's body doing another firing after such a short interval, it was good to fire again with the previous firing fresh in the mind.

Front of chamber with some of the bag wall visible, and a few small unglazed stoneware pots on top to get a natural glaze from the ash and flame. 
With the current layout of this kiln, all the heat comes in from the fire box at one end of the chamber, it hits a little wall (called a bag wall) to deflect the flame upwards and to spread it out.  After circulating around the pots, the hot gases are taken to the chimney via flue-ways in the chamber floor. I suspected that I had built the bag wall too high for the first firing and it had deflected too much heat away from the work that was in the lower part of the kiln, making for a cool floor and hot top.  So for this firing I made the bag wall about 6 inches lower, and opened it up more in places to let some heat through.

This made a substantial change to things.  When the chamber became hot enough for me to see the glow inside, I could see from the colour, that the bottom of the chamber now was a little hotter than the top, but it was more even.

It is inevitable in a small kiln like this, that there will be some problems evening out the temperature from front to back of the chamber.  In fact, with this design, I think it unlikely that it ever could be even, so the interesting and challenging thing to do is to try to understand the kiln, then make work that flourishes in the environments that the kiln offers.

This is a detail from a "sacrificial pot" placed where it would get struck by the flame more directly.   It did get a bit "over cooked" and the glaze blistered badly in places, but there were some nice areas like this one.  I am currently re-firing this pot in the electric kiln to hopefully heal up the blistered areas of glaze.

Whilst testing the kiln I am putting pots that don't matter much, in the most exciting part of the chamber, and the pots that do matter, nearer the back where the conditions are more predictable and stable.

A great relief to see these two that mattered at the back of the kiln, really well fired with no glaze defects.
One day I would like to get rid of the bag wall altogether, and use unglazed stoneware pots to take the initial raw heat and flame from the firebox.  I am doing that to some degree already, and the small stoneware pots that I placed in this position are glazing up nicely by themselves from the wood ash and flame.

Bill and his dog visited to see the kiln being unloaded.  Notice that I have easy access to the kiln through the firebox, once its top is removed.
I made this firing about ten and a half hours long, more than 2 hours longer than the first test firing.  I had intended to go for about 12 hours, but lost concentration a bit towards the end of the firing and allowed the kiln to come up faster than I really wanted.

Big planter, about 23.5 inches tall (600mm).  This looks so good outside in its natural environment. 

This one is a little bit taller at 26 inches (660mm).

The kiln is much nicer to fire with the new external firebox than it was in the past, when I had fireboxes under the kiln chamber.  In part this is due to having the stoke hole to the firebox at a height that I can reach easily whilst seated.  Previously I had to kneel to stoke, and the repeated stand up, kneel down, stand up, kneel down for 12 hours was extremely tiring.  I like the simple ladder grate in this firebox too, much less of a fiddle than a conventional grate, and I can easily fire in oxidation all the way up to earthenware temperatures.  All my other fireboxes with conventional grates have had a period around 750 - 900 degrees Centigrade, where reduction atmosphere happens almost automatically, and it has been difficult to fire them cleanly, thus far I am finding the ladder grate vastly superior.

The great unknown is if my firebox will continue taking the kiln up to stoneware temperatures.  It looks very promising so far, but I have known kilns to suddenly "run out of puff", so I will only know for sure when I try.

Garden snails, no garden is complete without them!!


John said...

Really nice progress here Peter.
Remind me to exchange some of my snails for yours - I much prefer them to have smiles on their faces!

Peter said...

Hello There John!
Yes the snails here are all happy snails, full of good humour and fun! They would love your lettuces!

gz said...

It is always good to have a follow on firing, developing ideas further or solving problems- and saving fuel, starting with a warm kiln!

At least it is supposed to be chilly where you are....!!

Angie said...

Another amazing collection of pots ... love the snail one too. I think it must be exciting not to know how they will actually emerge from your kiln ...hope it doesn't run out of puff.
As for weather ...we have been anything between 5 and 10 ...rain and even more rain, with the odd hour of sun. Hard to know what to wear when braving the elements. The other day it looked great and was maybe even 11 .... by the time I got where i was going it had dropped 4 degrees and a wind had picked up... by the time I got home I looked as though I had fallen in a pond lol

smartcat said...

More wonderful pots! You are showing me a new side of t!erra cotta. Love those snails

It's been a long up and down spring. Our mini drought ended in april....we've had plenty of rain for the last few weeks.

Linda Starr said...

I'm really loving those flutes on your pots.

Tracey Broome said...

You just don't take the easy road do you Peter! But the harder path sure does lead to some beautiful pieces of pottery!!!

Arkansas Patti said...

Love that big planter. Really different looking. Tending your kiln in the cool looks quite pleasant.
Interesting how you experiment.

Julia said...

I really like the big planter forms, too, and the glaze turned out so rustic and natural on the largest one. Thanks for sharing all of the information that you hvae on firing your kiln.

Peter said...

Hi Gwynneth,
A warm kiln would be the place to be today as we've got a 20km+ Southerly, 5 degrees C, and wind chill taking it down to 1 degree as I write this! Actually quite exciting in its way with lovely autumn leaves around the place.

By the sound of it, our part of New Zealand really is attached to Scotland somehow! Not knowing what you are going to get from the kiln is some of the attraction of wood firing for me.. When you load up the kiln, you have an idea about which parts will fire hottest, and where the flame might go, but there are a lot of unknowns too..., including the choice of wood to burn and the effect of the weather. Humidity and wind gusts can play their part on the final result.

Hi Smartcat,
I guess that I am finding new sides to terracotta myself with all this, and am starting to have all sorts of new creative ideas as a direct result of playing with this kiln.

Hi Linda,
I'm starting to appreciate the importance of surface texture, (something I've tended to put slightly to one side over the time I have been crystalline glazing), so much could be done with just the clay itself and with the action of the flame and ash with this sort of firing and clay, that a glaze becomes almost an optional extra!

Hi Tracey,
I don't set out to make things hard for myself... really, I don't!!..., but throwing wood onto a fire and shivering on a chilly morning is more like being alive for me than just flipping a switch, and it is good to be out there with the uncertainty of a wood firing again. When I think about it, I was just the same when I was a painter.

Hi Patti,
I like the big round planter best I think... it is quite hug-able! It is fun doing larger work, the result is much more on a human scale.

Hi Julia,
Good to hear from you. I like to share the information in the hope that it will encourage others to do some too.

Armelle said...

Great firing Peter, with courage !!! Nice pots and I love the snail's one too. The weather here is not warmful and it's May now !!!

Peter said...

Bonjour Armelle,
I think the garden snails might be a good design to put on other pots, it was fun to do and, who knows, the little pests that threaten my lettuces might turn out to make us some money!

Ah, the "warmful" weather of summer and winter! ... ours is similar to yours I think. I am writing this at 9.30 in the morning and outside it is about 6 degrees Celcius and quite windy. A day for hats and coats and warm drinks! For the cats it is a day for the electric heater and the wood stove! NS sends purrs!

Yana Out East said...

Those are stunning pots Peter. I'm in awe. Thanks for your last two comments, I'm not checking the blog much these days and just found them.

Peter said...

Thanks Yana, that is lovely of you, and good to hear from you too. Mmm it is hard to keep on top of the blog thing, I know I go through "seasons" of blog activity, then times when I almost quit altogether.