Trish0203 Posted June 25, 2021 Report Share Posted June 25, 2021 I have have about 20 pieces from last two firings that have had awful problems. No one else’s pieces that I know of w issues. My underglaze running (speedball, mostly black), clear glaze is dry with bumps and holes. I spend about 5-6 hours on my sunflower mugs. I have also made a couple mugs I need as parting gifts for friends that didn’t make it. I’m so frustrated and no one has an answer. I use the same clay I have always used (stoneware 182), speedball underglazes, studios clear glaze over. I tried using the pure brilliance to see if it was the clear glaze but having same issue. I just bought a Laguna clay to try but haven’t fired any yet. This came out of no where. I haven’t had these issues in past. Anyone have suggestions? Please!! I’m ready to quit! Link to comment Share on other sites More sharing options...
Min Posted June 25, 2021 Report Share Posted June 25, 2021 Few questions, are you having your work fired in a group studio kiln? Do they use witness cones? What cone are they firing to? Glaze on the cat mug looks underfired. When you say stoneware 182 is it this clay you are using? (if so there is another issue that should be mentioned; firing to cone 6 with a wide range clay can lead to absorption issues, pots can weep etc). Do you have the recipe for the studio clear glaze? Often running underglazes are because of a fluid glaze which pulls the underglaze down. Did you underglaze on bisque then glaze without the underglaze bisque fired? On the cat mugs how thickly did you apply the underglazes? Did you dilute them? How many coats? How do you apply the glaze? I know it doesn't help with your current mugs but going forward make up some tall test tiles and try out the underglazes and glazes on those before committing your "real" pots. Welcome to the forum. Link to comment Share on other sites More sharing options...
Bill Kielb Posted June 25, 2021 Report Share Posted June 25, 2021 When this happened to us it was the result of thicker and thicker applied underglazes to achieve 100% color coverage. Our tests indicated that some underglaze colors were more refractory than others. The fix was to create a clear that would melt better over these underglazes. Some folks routinely mix a little fritt into their underglazes to promote melting. Maybe this is something to test with your most refractory colors. Black, dark blue, Red I believe were the worst for us, although anything applied thick or 100% coverage had the tendency as opposed to wash style applications. The bleeding or smearing of sharp lines in the last two pictures is also interesting, something we never experienced but I usually spray applied the overglaze and made sure it’s application was even throughout by drying in between spray coats. The sugar bowl below would actually show these pinholes / bumps wherever outlined in heavy black and the yellow dot on the very top is just random brush spatter which ends up fairly thick. Most clears we tried did not melt right in those areas so what you see is a matte clear we made just for this use that would melt a bit sooner, say cone 4ish, in a cone 6 firing. We tested colors, thicknesses of underglaze and various clears on many test tiles and confirmed for us, that is what was happening and just how melty the clear needed to be to melt well in these areas. I would take some test tiles and shade them with various colors from thin wash to thick full color to confirm and to learn the limits of various combinations. Link to comment Share on other sites More sharing options...
Trish0203 Posted June 25, 2021 Author Report Share Posted June 25, 2021 Did you find a clear that worked? I will definitely the test tile w various coats. Thanks for feedback. Link to comment Share on other sites More sharing options...
Trish0203 Posted June 25, 2021 Author Report Share Posted June 25, 2021 Min, yes it is community kiln. Unsure if they visualize the cones but I can ask. (I am planning on getting my own skin) I use the studios stoneware 182 that can fire cone 6-10. I fire to cone 6. I don’t have recipe for clear glaze. I did try the pure brilliance but that mug had same issues. I didn’t think about the pieces not being fired correctly, but no one else is reporting these issues. I did send a few in to be bisque today so we will see. I do notice the bubbling more w darker colors as bill mentioned (burgundy, dark blue, black, red). The bleeding is a whole new issue. I am new to pottery and was having a thickness issue last summer and someone told me only one coat of clear glaze and problem was solved until now. I don’t sell my pieces. Just make them for fun and it’s not fun if they don’t finish right. I am trying a new clay from laguna. And I emailed speedball to see if they have suggestions. I am willing to make my own glaze or use a pre-made version if there is one with better results. Thanks again for feedback. Link to comment Share on other sites More sharing options...
neilestrick Posted June 25, 2021 Report Share Posted June 25, 2021 182 ius underfired at cone 6. The clay does not fully vitrify until cone 10. Since you have access to Standard clays, use clay body #630, which is the cone 6 version of 182. Most Speedball underglazes work very well at cone 6, however Royal Blue and Red will cause bubbling/roughness in the glaze at that temp. Use Medium Blue and Carmine instead. Speedball underglazes are really thick in the bottle, and should be thinned down before use. 3 coats of thinned underglaze on leather hard clay or 2 coats on bone dry or bisque will generally cover quite well. If you're using 2-3 coats straight from the bottle the underglaze will likely be too thick, and cause problems with the glaze. Speedball underglazes also work better if you apply them before bisque firing, so the binders and hardeners can burn out in the bisque. Otherwise they tend to resist the glaze and you won't get great coverage. Link to comment Share on other sites More sharing options...
Bill Kielb Posted June 25, 2021 Report Share Posted June 25, 2021 49 minutes ago, Trish0203 said: Did you find a clear that worked? I will definitely the test tile w various coats. Thanks for feedback. We mixed our own until we had something suitable. We have a matte and gloss for the occasion and then made it available as a studio glaze after a year of testing to which it has been great. Have given it here with mixed results as glazes often don’t travel well. Here is the matte recipe we published on Glazy several years ago: https://glazy.org/recipes/19734 It has a very positive review from Irene who experienced what we have, but there are many who do not find the same. As a community tested glaze it still works for us. The Fritt solution might be an easy one for you if you are experiencing this same problem. As always, test and learn the limits of what you are using. Link to comment Share on other sites More sharing options...
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