I am writing this as the kiln is starting to heat up again with the second glaze firing of the week. The first firing was important as it had two of my 4 angels on board, as well as more bowls and cups. In many respects this firing was a test for the one I have on now. I was fairly sure, but not certain, that the glazes that I put on the angels would work well together, but I really needed to check that there would be no unpleasant surprises, either with the glazes, or with the angel structures when fired to glaze temperature.... At 1280 degrees Centigrade (2336 F) it was always possible for wings to droop, or bodies to distort or split as clays can become pyroplastic when nearing vitrification, which is a nice way to say that they can get as weak and as droopy as chewing gum! With stoneware this is usually not much of a worry when firing bottle shapes or simple vases, but it can be an issue with wide bowls with thin rims, or with sculptural work. The situation is far more risky with porcelain. Anyway, I digress...
In the kiln, the angels looked rather brave and heroic standing amongst the tea cups and bowls. I felt rather mean closing the kiln lid and switching on the power when I thought of the incandescent hours that awaited them. Happily both angels survived trial by fire and greeted me enthusiastically when I opened the kiln at the end of the firing! The wings had held together splendidly, and there were no disasters with glazes.
The remaining two angels are in the kiln that is firing tonight, and lots more bowls.
I like to put a test glaze or two into most of my firings if I am organized enough. One that looks promising from the last firing was a gentle cobalt violet coloured glaze. The glaze base is a white glaze that is in John Britt's Cone 10 Glaze book (The Complete Guide to High-Fire Glazes).
The glaze is called "Buttermilk" and it has an attractive texture something like an egg shell, but whiter and a touch more shiny. The glaze is nice on its own, but I had a hunch that it would make a nice cobalt violet, because the glaze contains quite a lot of magnesium*, and magnesium and cobalt tend to produce purple, or violet.
I made it as follows:
Potash Feldspar 29.3 (the recipe says Custer Feldspar but we don't have that in our part of the world).
Gerstley Borate 10.5 (I still have some of this, but you could use Gillespie Borate or another substitute)
To this I added cobalt carbonate 1
This was fired to Orton Cone 10.
|This purple was hard to photograph, the colour is stronger and warmer than it appears here.|
I like the result. There is an interesting dark "break" where ever the glaze is really thin, like around the rim, and an attractive violet elsewhere. I will try a line test with more cobalt, and also play with adding iron oxide. I noticed that red iron oxide produces a very attractive straw yellow colour when painted over the original white version of this glaze, and the white plus 2 - 4 percent red iron oxide might be very nice indeed.
(*magnesium, for those who might be wondering, this is contained in two of the glaze ingredients, namely, Dolomite, and Talc. Dolomite is magnesium carbonate, and Talc is magnesium silicate.)
We will be taking part in another craft show this coming Saturday. This will be held in North East Valley, Dunedin. The event is being organized by Northern Artery, an arts and performance collective. I know nothing about them, but it is nice to be able to take part. Northern Artery have a Facebook page with more information about the event and about the artists and crafts people taking part NorthernArtery.
Arts and Crafts Bazaar
Saturday, 1st of December from 12 till 4pm at St Martins Hall, Northumberland St, North East Valley, Dunedin.