Summer has just begun, so now it’s time to use the last bits of winter …. in my ash glazes.
Last year I had a conversation with a befriended couple, about wood turning (friend ) and ceramics (me). A wood turner often uses the same design language as a potter and I think both have a great passion for the art of the profession, so for us, there are always plenty of things to talk about. Such as “who turns wood, will perish in wood shavings“.
But the raku ceramic artist is happy to help a wood turner with this problem, as smothering the raku pots happens after all often in a sawdust bucket. You understand, I could get a lot of sawdust from my friend ….. but apart from that I do not have enough room for storing so much sawdust, I fire raku too little to have use for it.
However I would like to have the ash (also needs a lot less space, only 10 to 20 grams remains from about 1 kilo of wood). And as you will guess, my friend could also provide me with this, not because he is a wood turner, but because they keep their cosy houseboat warm in winter with a wood stove.
So, after the winter months, I could pick up a few kilo of ashes, but what to do now?
Ashes
All ashes of plants (or animal) may be used as a fluxing agent in glazes. Generally in stoneware glazes (1250 °C or higher), but also in mid temperature- (1150 °C) or earthenware glazes (1050 °C). At lower temperatures, the ash alone will be insufficient to melt the glaze, but in combination with another flux (such as a frit) it can be done.
All the ashes have a different composition, even the ashes of the same plant can be a (slightly) different depending on where they have been cut, in what type of soil or even what time of the year picked or cut down. As this raw material of glazes can vary so much, the glaze will every time be surprisingly different.
Dry sieving
Before you can use ashes in a glaze it needs to be cleaned, which can be done by washing (with water) or (dry) sieving. Ashes of grasses should generally be washed with water (and after that dried), wood ash can also be (dry) sieved to be used immediately.
As the ashes are washed with water, a portion of the fluxes will be “washed away” (a part of the alkali metal salts in the ash dissolves in the water). Thus, the washing or sieving of the ash also makes a difference in the “melt strength” which it will have in the glaze.
I have chosen to dry sieving the wood ash. For this I used a 60 mesh sieve and rubbed the ash through it (twice). Since this is a bit dusty job, I’ve done this outside on a windless place.
Ash glazes
After the hard work, the fun could begin; making tests. The first thing I did was firing the ash into a small bowl (in reduction) to about 1220 °C (cone 7 to 8). My “normal” temperature for glazes. After the firing, I could see that if the ash was not too thick, it already melted.
Then I experimented with mixtures of the ash, quartz and kaolin. The result was a nice glaze with a subtle green colour (the iron in the ash). This glaze I made in a larger amount. After mixing with water, the glaze appeared “to fatten” after a while . This is a reaction of the dissolved salts in the water (I had to wash it, instead of sieven).
Adding more water is possible, but that results in a very thin glaze layer on the pots, it is better, therefore, to add a small amount (max. 0.2%) of waterglass (sodium silicate). A small addition ensures directly that the glaze is more fluid again (amazing to see).
But I experimented also with spraying 100% ash on my work (see photo of “bottle bird”). And then comes the most obvious character of the ash upwards, a kind of tranquil water, a trace of winter on a summer pot.
The lesson of this week 🙂
So you see that the waste of one person, could provide another person fascinating glazes …………
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