Monday, 14 April 2008

Moment of truth............

You know a couple of posts back, I was musing along philosophical lines and saying how much I enjoy what I do.

Well I stand by that.


There is one element of porcelain production which is just mind-numbingly tedious and boring. And frustrating.
And sometimes infuriating.


Sounds innocuous doesn't it?

Don't be fooled. It entails having your hands in tepid water for hours on end, painstakingly removing seam lines and imperfections left on the castings after they've been released from their moulds. The greenware is soft-fired first, to create impermeable castings which won't revert to sludge when soaked in water. This makes them stronger than in their original state, but they are still very fragile and fingers especially are liable to ping off at the slightest pressure.
However, it must be done.
It's only saving grace is that I get to listen to Radio4, uninterrupted for hours at a stretch while my hands shrivel to prunes.

Anyway, after sometimes several days of this tedium, there comes the relative excitement of loading the kiln with shelf after shelf of tiny bodies, arms and legs and setting it to fire.

The bisque firing takes a long time. Up to 8 hours if the kiln is very full. At the height of the firing the temperature reaches 1215 degrees Celcius which is very , very hot.
Small dog loves firing days and I can gauge the temperature in the kiln without resorting to looking at the LDC display, just by seeing how close she can lie to the kiln.
Heat shimmers above it, which on cold days is lovely as it can heat the whole of the ground floor of the house. Peeking at the slight gap between the lid and the body of kiln revels a line of bright, white heat.
During this infernothe extremely fragile greenware is vitrified into slightly less fragile porcelain. Magically the colour changes from a chalky white to glowing flesh tones, depending on the colour of porcelain slip used for the castings. Each piece also shrinks by up to 1/3.

Over my almost 20 years as a porcelain dollmaker, the anticipation of opening the kiln after a bisque firing has never diminished. The kiln stays very hot for hours after it reaches the end of its programme so it is usually next day before it is cool enough to open.

Lifting the lid is the moment of truth.

If the firing has gone well, there will be serried ranks of little flesh coloured heads, bodies and limbs and sighs of relief all round.

If the firing has gone badly, there will be wails of anguish and sometimes even tears of disappointment and frustration.

An underfire is the least bad 'bad firing'. As the kiln elements age, they struggle to reach the highest temperatures and keep them there for the required 'soaking' period. This produces an underfire. The porcelain is not fully vitrified and has a dull, chalky appearance. The colour does not fully develop and the pieces do not shrink to the correct size, which of course is vital in a scale piece.
This, though frustrating, is at least capable of being put right. Underfired pieces can be refired to the correct temperature, although of course it is wise to replace the ageing elements first. A costly and tricky procedure which most kiln owners put off till the last possible minute. The minute after an underfire.

Overfirings are a complete disaster. I have only ever once experience an overfire, and every single piece in the kiln......the result of many weeks work, was lost.
On that occasion I was using my old, manual kiln, and a prop fell against the kiln sitter (a low-tech, mechanical way of switching off the kiln at the required temperature) and jammed it so that it didn't shut down the kiln.

So the temperature rose, and rose, until the smell of the floor melting under the kiln alerted me the fact that something was badly wrong.

Overfires turn the porcelain pieces into glassy objects, completely white, or completely black, depending upon the porcelain slip. I had hopes of using some of the less glassy ones as ghosts but china paint wouldn't adhere to the surface of the faces, and anyway, most of them were blistered on one side where the extremes of temperature had blasted them.

I now have a computer controlled kiln, in which overfires should never happen.


There is always a first time for everything.

However, when I opened the kiln this morning, I was relieved to find that it had gone well.

Which I never, ever take for granted...........

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