Cadaola Posted May 4, 2015 Report Share Posted May 4, 2015 Hi! I fired this clear glaze at cone 6 (1230°C) and it comes out of the kiln sometimes very good, somethimes with some flaw, as you can see in the attachted pictures. Clear glaze (cone 6-8): Feldsp potash 34 / colemanite 14 / whiting 11 / EPK 13 / silica 23 / dolomite 5/ Once I substituted colemanite with a boro-calcium frit (because of solubility), but the problem remains. Regarding the glaze with green underglaze, the flaw is shiver or crawl? (or something else?) And regarding the bubbles appearing on the blue underglaze, what should I do? thanks! Paola PS: because I have these problem long since, I carefully clean my pots before glazing. I pour the inside and dip or gun spray the outside. Link to comment Share on other sites More sharing options...
Pres Posted May 4, 2015 Report Share Posted May 4, 2015 What bisque temp? Are you firing right after glazing? I have had some problems with one glaze over another, and firing too soon after glazing. Water in the bisque ware will turn to steam causing some problems with glaze in early part of firing, often spitting. At the same time, if the surface loosens up because of steam, crawling will happen. Just a few thoughts. I now water smoke until the kiln exhaust if clear of water vapor. Link to comment Share on other sites More sharing options...
Min Posted May 4, 2015 Report Share Posted May 4, 2015 Looks like crawling in the first 2 pictures. In the last picture it looks like the underglaze isn't adhered to the pot and is lifting up during glaze firing. When do you apply the underglazes, leatherhard, dry greenware, bisque? Is it a commercial underglaze or your recipe? Link to comment Share on other sites More sharing options...
Babs Posted May 4, 2015 Report Share Posted May 4, 2015 Interesting that the effect is not occurring where the green underglaze has been applied. I'd be really stirring the blue underglaze and adding a flux. the underglaze I use needs flux to avoid a blistering and non melting. I get a more bloaty effect if the underglaze is applied at a too dry stage of leatherhard. Link to comment Share on other sites More sharing options...
Cadaola Posted May 5, 2015 Author Report Share Posted May 5, 2015 What bisque temp? Are you firing right after glazing? I have had some problems with one glaze over another, and firing too soon after glazing. Water in the bisque ware will turn to steam causing some problems with glaze in early part of firing, often spitting. At the same time, if the surface loosens up because of steam, crawling will happen. Just a few thoughts. I now water smoke until the kiln exhaust if clear of water vapor. BISQUE: 60°C (140F) /h to 120°C (248F), soak 30 min. 100°C (212F) /h to 600°C (1112F) 80°C (176F) /h to 980°C (1796F), soak 30 min. I always clear my bisqued objects with compressed air and sponge them with just a little water. In this case I thin gun sprayed the glaze, and waited 2 days before firing. The green glaze is an underglaze already bisqued at the time I glazed over with the clear glaze. I am sorry, because of my poor english, I don't understand what you mean for water smoke... could you explain to me? Thank you! Link to comment Share on other sites More sharing options...
Cadaola Posted May 5, 2015 Author Report Share Posted May 5, 2015 Looks like crawling in the first 2 pictures. In the last picture it looks like the underglaze isn't adhered to the pot and is lifting up during glaze firing. When do you apply the underglazes, leatherhard, dry greenware, bisque? Is it a commercial underglaze or your recipe? "In the last picture it looks like the underglaze isn't adhered to the pot and is lifting up during glaze firing." Exactly! I apply the commercial underglaze at leatherhard stage. Link to comment Share on other sites More sharing options...
Cadaola Posted May 5, 2015 Author Report Share Posted May 5, 2015 Interesting that the effect is not occurring where the green underglaze has been applied. I'd be really stirring the blue underglaze and adding a flux. the underglaze I use needs flux to avoid a blistering and non melting. I get a more bloaty effect if the underglaze is applied at a too dry stage of leatherhard. Actually sometimes it occurs over the green underglaze too Thanks for you suggestion I will try to add some flux. I also experimented a more bloaty effect if the underglaze is applied at a too dry stage of leatherhard. So I put it on at not too dry stage, but it works only sometiimes. Link to comment Share on other sites More sharing options...
Cadaola Posted May 5, 2015 Author Report Share Posted May 5, 2015 How much flux would you recomend to add? Link to comment Share on other sites More sharing options...
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