Thrown_In_Stone Posted October 21, 2012 Report Share Posted October 21, 2012 Hi everyone, I have been using a glaze from the following recipe (from the book 'Colour In Glazes' by Linda Bloomfield): 39 Calcium Borate Frit 27 Soda Feldspar 5 Whiting 6 China Clay 23 Quartz _____ 100 _____ I expected this glaze to be a little more transparent and a little glossier. It is slightly under-fired, it's a cone 04 glaze and I fired it to 1050ºc by accident, I believe it should be around 1060º-1070ºc. Can this amount of under-fire cause the glaze to be not as transparent and have a satin finish instead of gloss? I also tried adding 0.5% Cobalt and it turned out a matt/satin opaque blue. I have used 0.5% Cobalt in a transparent glaze before and it came out perfectly, semi transparent and glossy. Other than the problems listed above the glaze works quite well, doesn't run, and fits my clay body well unlike most of the transparent glazes (commercial) I have tried. My questions are: - Can 10-20ºc underfire cause these issues? - If I re-fire to the correct temperature will it give better results? - If I fire new pieces to the correct temperature will it be better? Thanks for any advise you can give. Gary Link to comment Share on other sites More sharing options...
perkolator Posted October 23, 2012 Report Share Posted October 23, 2012 sounds like you've been using this glaze in the past with success? if so, was this round produced using a fresh batch of glaze? if so, there's the possibility it wasn't weighed correctly this time, but you'd have to fire to correct temp to know. a 10-20*c difference in temp is quite a bit and is almost a whole cone difference, so it's very possible that this batch was simply under-fired and it didn't flux out like it should have. try re-firing the pieces and hold at temp. next time, try firing to correct temp as this is truly the only way to know if there isn't a problem with the glaze. Link to comment Share on other sites More sharing options...
bciskepottery Posted October 24, 2012 Report Share Posted October 24, 2012 At ~1050 degrees C you reached about cone 05; 1070 degrees is about cone 04 . . . so you underfired by one cone. What frit are you using for the "calcium borate frit"? You might want to try a couple test batches with different frits to see if that affects transparency and glossiness. Are you firing on white or red/brown clay? There could be ingredients in your clay body combining with the glaze incredients that could be causing the glaze to behave differently than what the book shows/tells. Link to comment Share on other sites More sharing options...
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