March 25, 2019
Of all the things I make, a good many of them acquire a crackle finish through Raku firing. How that happens is as follows. I start with the sculpture I want to make. That could be anything, a mask, an urn or a figure. When the initial shape of the work satisfies me, the clay can dry. The parts that need colour will be painted with an under-glaze, which works like water-colour paint for ceramics. Ordinary water-colour paint would burn in the oven, this is ceramic material. Then the work is fired in an electric kiln to 1020 degrees (in a computer controlled program that takes about 16 hours to heat up and then a day to cool down). Subsequently it is glazed. The glaze also needs to melt, so I return it to the kiln, again at 1020 degrees. This gets the glaze layer rendered down well. If you try to do that in one session in the Raku kiln the whole firing process will take much longer and you don’t know for sure if the glaze is transparent like you want it. You might risk a white, bumpy layer that I don’t like except maybe for some specific items.
After that it needs a third firing in a different kiln, an outside gas kiln made from an oil drum, my Raku Kiln. I raise the temperature up to 1000 degrees (quite fast in about 45 minutes) until the sculpture is red hot and the glaze layer has melted again. I then take it out of the oven with large metal thongs (and gloves of course, it is all extremely hot). I put the work down and listen to make sure the crackling of the glaze layer takes place. The reason this happens is because the ceramic cools down very rapidly from 1000 degrees to the ambient temperature of 20 degrees. The ceramic and the glaze do not shrink the in the same way, that’s what causes the cracks in the material. These cracks may continue deep into the clay. It is, in a way, a rather unkind technique for ceramic.
When I hear the work tinkle, crackle, I pick it up using thongs again and put it into a barrel filled with sawdust. This sawdust will catch fire and I then cover the barrel with a lid. This extinguishes the flames but it will continue to smoulder. The smoke inside the barrel works its way into the cracks and all the spots without glaze. After fifteen minutes I take it out of the barrel. The sculpture is now completely black. It can cool down and has to be washed. If the cracks go really deep I apply a small layer of glue to prevent it from breaking. The glue is on the backside so it doesn’t show. And if the whole sculpture is indeed unexpectedly broken I also glue it back together using white joiner’s glue that becomes transparent when dried so you won’t be able to see it. I make no secret of that procedure.
Eventually I apply a suspension thread and make some photo’s for my own documentation.
And than, finally, the art work is finished and ready to travel on to its new owners.