Friday, 11 February 2011

All fired up............

This was the scene inside my kiln when I opened it yesterday.

I find it completely mesmerising but then I am a bit of a kiln geek.

Those arms and legs in the middle are the final, last ever 1/12th scale limbs I will ever make.  They will be united with my remaining head-torso characters to create the last few dolls kits to be made and sold by Tower House Dolls.

End of an era and all that.

Most of the tiny stuff around the edges are 1/24th scale dolls and toys, destined for some of my new kits to be launched at Thame. 

However, this latest bisque firing has revealed to me that I absolutely MUST bite the bullet and replace the kiln elements.  Over time, with repeated high temperature firings, the elements (which are the curly wires around the sides) deteriorate, and it takes them longer and longer to reach the temperature required to vitrify porcelain (a bisque firing goes up to  1200 degrees Celsius).  

When the elements are new, I can achieve a perfect bisque firing in around 5 hours.  This last firing took 10 hours, which is not good, either for our electricity bill, or the porcelain.

Ceramics is a complicated science.  It's not just a matter of bunging stuff in the kiln, switching it on and hoping for the best.  Achieving a perfectly fired piece requires a knowledge of heatwork, which is the combined effect of temperature and time.  For example, if my kiln is struggling to reach the top temperature, and taking many more hours to get there, the porcelain risks being overfired.  

An overfire is disastrous.  The porcelain gets tiny bubbles on the surface, acquires an unhealthy sheen, the colour is bleached out, and in extreme cases can actually collapse into a solid glassy puddle.

Luckily, I didn't have an overfire, but I estimate that another 30 minutes would have done it.  So I will have to buy replacement elements, at an eye-watering cost of over £100! I always replace them myself saving the cost of an electrician...... it's not difficult and over the past 20 odd years I've done it loads of times.

So the next time I do a bisque firing, it will complete in half a day, quick smart.
In the meantime, the three china paint firings, which only require a top temperature of 675 degrees Celsius, will be done over the weekend. Then there's the grit scrubbing, matching up of tiny jointed arms and legs, the stringing......

I might, just might, manage to get it all done in time.

*fingers crossed*

1 comment:

Elga said...

What memories you bring back, it is over 10 years since I have used my kiln, way too long, I have promised myself that after Guild School in Castine is over this June I am going to make time for dolls, 1/12 scale though to start off with, well have fun and hope all goes well. Hmmm, I probably need to check the state of my kiln!!!!