Friday, July 29, 2011

It's about Atmosphere: electric firing with cooking oil drip reduction.

Titanium white pot fired in reduction.

 Just after sundown, a clammy fog rolled in and covered the village.  It blotted out the church spire altogether, and even people still brave enough to walk the narrow stone pavements reduced their speed.  Footfalls were muffled, the street lights became dim and haloed, and the chill, damp air seemed to catch in the back of the throat.

This was a copper green pot, now copper red through the oil drip reduction firing.

It is all about atmosphere!  Sunshine, wind, fog, darkness, make us feel different moods, from bliss to terror!  In the kiln, atmosphere can dramatically change the appearance of a pot.  Give it oxygen, and the colours will probably be brighter and clearer.  Starve the kiln of oxygen, and introduce some carbon monoxide, and the pots will have an entirely different mood and may turn dramatically different colours!

The two front pots were pale green and ivory white before reduction firing, and the two at the back share the same glaze.  The white one is oxidized, and other is fired in a reduced atmosphere!

In a wood fired kiln or gas kiln, it is possible to control the atmosphere whilst firing.  Just adding a little more fuel than can be easily burnt will deplete the kiln of oxygen.  An electric kiln normally doesn't offer that choice.  You switch the thing on, the elements glow, and the kiln atmosphere will be mostly neutral to oxidizing, depending what you have in it.  Of course some of us like to experiment.   Potters have done all sorts of things, including firing gas or oil burners into electric kilns, or dropping in moth balls, sugar cubes, or thin sticks of wood.  In a regular electric kiln this can be hazardous, hard on the kiln elements, and not always reliable. 

Rutile glaze, first an ivory white in oxidation, now soft green and purple in reduction.

I have been playing with re-firing crystalline glazed pots in reduction atmospheres (reduction refers to reduced oxygen).  My first experiments were with a small wood fired kiln that I made for the job.  Some of the pots from these firings were lovely, others were not, but it was an interesting and exciting way of working.  See my post "Crystals in the smoke!" for some photos of wood fired crystalline pots.  A few days ago I did my first cooking oil drip reduction firing in an electric kiln with some crystalline glazed pots, and the results were very successful.

What happens when an artist's easel, a lawnmower petrol tank, a short length of tubing and a kiln get together in a confined space!
My equipment for the firing was fairly eccentric looking.  An old lawnmower petrol tank was attached to an artist's painting easel.  From the tank a piece of clear flexible tubing led to a metal pipe, and this entered a ceramic tube which in turn entered the kiln through a spy hole.  The clear tubing had a home made adjustable clamp on it to control the flow of oil.  Inside the kiln was an unglazed stoneware shallow bowl with a round piece of insulating fire brick in it.  The oil was directed to drip onto the insulating fire brick.  Immediately below where the tube entered the kiln I cut a slice of insulating brick and used it to protect the kiln elements to prevent any chance of oil dripping directly onto them.

Oil drip reduction fired copper glazed pot from the top.

The firing was quite simple, just a question of taking the kiln up to about 800 Celsius (1472 Fahrenheit) , switching it off, then adjusting my cooking oil drip apparatus to give approximately one drip of oil per second through the tube into the kiln, and keeping that going until the kiln had cooled to about 600 Celsius (1112 F).

Copper glazed pot. The mild looking reduction was sufficient to turn this not just red, but also quite metallic looking.

I did undertake the exercise with considerable care as I have only read about this procedure and have not seen it done.  I changed out of the polyester jacket I was wearing and put on cotton overalls, and I kept not one, but two small fire extinguishers within easy reach just outside the shed door.  Some of you will know from cooking, just how dramatic a cooking oil fire can be, and I wanted to be able to make sure that it was possible to keep one under control if something went horribly wrong.

I was tempted to give this a reduction firing, but like it too much as it is.  This pot reminds me of the recent snow that we have had here.

As a wood firer, I was intrigued to see just how little visible smoke was seeping from the top bung of the kiln, and I did wonder if the oil drip would be sufficient, but I am happy to say that the results were dramatic! 

Here is a close up of the pot with the rutile glaze fired in reduction.

In the first firing I kept up the oil drip for three hours.  In the firing that I am doing as I write this, the drop in temperature is much faster, and I will be shutting off the oil drip after two hours.  It will be interesting to see if there is any noticeable difference in the way the pots look.


Angie said...

That copper glaze /oil drip pot is gorgeous ...they all are I wish i could see them in real are never quite the same

Peter said...

Hello Angie,
You must be sitting there at the computer at the same time that I am, but on opposite sides of the world! Quite a thought! Photos are a bit frustrating really, I quite agree, and I wish that there was a way to do things better. It is a shame that the teleporting thing that they had on Star Trec wasn't real (or was it??)... Then we could say "Beam me up Scotty." and be in another part of the world in an instant, or maybe beam a pot over to you that way! Oh well! :)

gz said...

Dave Binns has been at the Ceramics Centre in Keskemet in Hungary, posting reports of a smoke free woodfired kiln! Only on facebook so far, not on his blog yet!

Pat - Arkansas said...

Love those pots, especially the copper ones! Gorgeous! The oil drip method had great results. Glad you took extra safety precautions; we can't have you singed around the edges.

Arkansas Patti said...

Copper glazed pot won me over too Peter. All your work is wonderful, this one just really catches the eye.

Judy Shreve said...

These pots are just gorgeous! And oil drip & open fire - now that's atmosphere - I'm glad you took extra precautions too!

Linda Starr said...

You are such an adventurer, right after my own heart, with that oil drip reduction, good for you.

Peter said...

Hi Gwynneth,
Thank you for the link to Dave Binns it all looks most interesting. I think that quite a lot can be done to reduce smoke when wood firing, both in terms of kiln design and also intelligent stoking. It is definitely something that I am thinking of for when I make my next wood fired kiln.

Hi Pat,
Glad to report that my beard is still intact! This reduction firing thing is fascinating. Have just unloaded another few pots from the kiln, and more dramatic results that will be posted soon.

Hi Patti,
That's nice! "All... Wonderful"! Well, you don't see the ones I throw away! But it was a good firing, which is always a blessing.

Hi Judy,
Thanks Judy. I wonder what comes next after oil drips.... I did hear that someone was thinking about hydrogen into an electric kiln..., but I don't think I will dare go that far!

Hi Linda,
Yay... Adventure! Did you ever read "The Wind in the Willows"? with Toad and his canary coloured cart, and his series of motor cars?? He was a fellow adventurer, and should probably be our mascot!

Angie said...

Just dropped by to give you an up date on THE tree. Most are dead in the area ...must have been much colder than I realised, over the winter...BUT ...I thought about what you said about dead trees showing new life and there, all round the base there are new shoots ...not sure what to do next ??????