Recently I fired my standard clear glaze.(Potash Feldsspar 19, Silica
19, Wollastonite 25,Podmore frit 2953 25,Microwhite China Clay 12.) (This glaze started out as the 20,20,20,20,20 glaze on the Digital Fire web site)on a buff stoneware clay. Electric kiln fired to between cone 6 and 7.
The glaze was coloured with the addition of 5% red iron oxide and 5% rutile. I used this combination after doing a cross blend. When it was fired the rutile had formed patches of blue crystals where the glaze was thick. These crystals also formed over a low fired stoneware white clay as well but were not as obvious. The questions are Did the rutile react with the iron oxide? Did the rutile react with the boron in the glaze? Did the rutile react with something else in the glaze? Could I get more crystals if I increased the rutile, iron or boron? Do the crystals form on the firing cycle or on the cooling cycle? If they form on the cooling cycle would a controlled cooling give more crystals? Cheers John W