My first glaze test tiles have come out of the kiln, frankly with quite disappointing results. I used the recipe for a Blue grey speckle glaze from Emmanuel Cooper’s glaze book, firing range 1050-1100C. The top tile shows the glaze on LF (low firing) white earthenware which results in a flat, brash blue colour that reminds me of children’s poster paint. The bottom tile shows the same glaze on terracotta which is slightly more green tinged and has visible speckles. I’d hoped for something more subtle. Maybe I accidentally overdid the cobalt oxide.
Calcium borate frit 20
High alkaline frit 15
Standard borax frit 25
Feldspar (soda) 18
Zirconium silicate 8
Cobalt oxide 1%
Frit – Raw glaze materials that have been melted together and reground before being included in the glaze slop for a variety of reasons e.g. so that soluble minerals become insoluble or hazardous substances (like lead) become less harmful.
Whiting – Calcium carbonate. A source of Calcium oxide for glazes.
Rutile – Titanium oxide with up to 25% iron oxide.
Cobalt oxide – The most powerful colouring oxide, gives a strong blue.