Testing Times

Recently I discovered that small, two-inch high bottles make perfect test pieces for trying out small amounts of glazes.  They are just the right size to dip into a 100 ml glaze pottle and are very attractive when fired. They look much more interesting than the traditional test tiles and also give me a much better idea of what the glaze will look like on a finished pot.  Making the pots is also a great way of exploring form. I am currently using them to try out variations on some of my favourite glazes  including copper red, shino, tenmoku and celadon.

In the 'lab' dipping a test pot into 100 ml of shino glaze

Test pots arranged in the gas kiln

Fired test pots - shino in front, celadon and tenmoku, copper red.

Different shino glazes, using different feldspars. The one on the far left is my original shino recipe, using washing soda crystals from the supermarket, the second from the left is the same recipe but using soda ash from the glaze room. It gives a more fluid melt and also appears to be really good for carbon trapping. When using these materials I found that dissolving in warm water first made the sieving much easier.

The copper reds - different recipes used over buff stoneware and white clay. Done in a reduction fired gas kiln. I hope to refire these same test glazes in oxidisation to produce copper greens.

A selection of variations on some of my glazes including twenty celadon glazes at the back, twenty shinos in the middle, and twenty tenmokus in the front. Not only am I looking for an attractive glaze, but also how it behaves in the bucket - so that it doesn't 'pack down' like a rock, and is easy to stir, sieve and apply.

Kiln opening

Here are the results from the gas reduction firing we did on Thursday. The pieces were glazed in two classic Chinese reduction glazes - Celadon and Copper Red. They were fired to 1300 degrees C (Cone 10).  A 'reduction' means that the oxygen is shut off to the kiln, creating a smoky atmosphere, starving the glaze components of oxygen.

The iron that gave the celadon glaze a pink appearance before firing (see the last post) is transformed to a beautiful pale green, and the copper- which would turn bright green in an oxidised firing - is a deep red, hence the name: Copper Red.

Here's a short video we made showing the kiln just after opening the door - you can hear the celadon making little 'ting' sounds as the glaze cools down and cracks. Days later, the pieces are still going 'ting!' from time to time as the glaze continues to develop its crackle effect.

http://www.youtube.com/watch?v=PUtkAU3IXAo

And a You Tube video showing the traditional techniques of Longquan celadon in China:
http://www.youtube.com/watch?v=U3kU52xtu4E