Last Tuesday I fired up the small gas kiln at Bath-Spa Sion Hill Campus, with very mixed results. It is a tricky kiln to fire, with the single gas burner positioned right beneath the thermocouple on the right wall of the kiln and a rather temperamental gas knob. The firing results were fairly bizarre, in that the top shelf reached cone 9-10, but the bottom barely reached cone 7, with only cone 06 fully down.
However, I made some useful observations. First of all, the Tenmoku glaze Rich Winfield introduced me to, fired very well across all shelves, and after a discussion with Rich, it may well be that the high iron content helped flux the glaze even at low temperatures in reduction (see the rows of mugs below). The beach clay Tenmoku, which has so far been a real success, came out almost metallic, and there was some crawling – similar to some of the pots I fired in my electric kiln over the weekend. I have an idea as to why the crawling takes place. The crawling seems to only occur where the glaze dips join, for example on the rim and where there is no real overlap. There seems to be an issue with discontinuity with this glaze – and it seems to work best when the glaze is applied either all at once, or when the glaze poured in / out on the inside, is then immediately followed with a dip for the outside (i.e. – when the glaze is still damp – which may help the glaze join?). There may also be an issue where this glaze is too heavy / thick.