yedrow Posted October 9, 2013 Report Share Posted October 9, 2013 I'm having an issue with one of my glazes cracking as it dries on the bisque. The problem is worse when it is put over another glaze. This of course leads to crawling on the fired ware. I've tried using Veegum T to toughen it up, but not to much effect. I have just inherited some CMC, but I don't know how to use it. Is that a possible solution to this problem? Or do I need to do something else? Joel. Link to comment Share on other sites More sharing options...
bciskepottery Posted October 9, 2013 Report Share Posted October 9, 2013 Maybe try adding some bentonite to the glaze; the glaze may not have enough clay in it so it is shrinking and cracking. Link to comment Share on other sites More sharing options...
Marcia Selsor Posted October 9, 2013 Report Share Posted October 9, 2013 Maybe thin the glaze a bit. Sounds like it is going on too think. Marcia Link to comment Share on other sites More sharing options...
yedrow Posted October 10, 2013 Author Report Share Posted October 10, 2013 I'll try the bentonite. From what I've read though, bentonite can cause the same problem. I was trying to avoid this effect. Would a 1-2% mix avoid exacerbating the problem?Marcia, It is pretty thin and I still have the problem. At the moment the glaze has a specific gravity of 1.47. I need a solution that will keep this sg. If I'm understanding the articles I've read about CMC, it can toughen the glaze. But, I don't know how to use it. From what I've read there is a learning curve to this material. Joel. Link to comment Share on other sites More sharing options...
Mark C. Posted October 10, 2013 Report Share Posted October 10, 2013 I'm not a big gum user but have used it in salt kiln coatings for adhesion. heres the ceramic arts daily stick- Carboxymethylcellulose (CMC) — an organic gum used as a suspension/adhesion agent in glazes. Normally, a small amount of gum is added to a quart or so of warm water and left overnight. Once dissolved, this solution may be added in small doses to glazes, slips, and engobes to improve application performance. Source: Clay: A Studio Handbook Link to comment Share on other sites More sharing options...
Min Posted October 10, 2013 Report Share Posted October 10, 2013 Is there a large amount of kaolin in the glaze? If so then calcining 1/2 of it would reduce shrinkage / cracking. Link to comment Share on other sites More sharing options...
minspargal Posted October 10, 2013 Report Share Posted October 10, 2013 That usually happens to me with commercial glazes that get too dry in the jars. i have tried remixing with water, using the additive Amaco sells and nothing seems to revive them. Now i just throw them out if i see them cracking on the bisque.I hate to throw money into the trash can. Anyone have any luck with this? Link to comment Share on other sites More sharing options...
yedrow Posted October 13, 2013 Author Report Share Posted October 13, 2013 This is the recipe. There isn't a lot of EPK in it so I don't think that is the problem. Custer Feldspar............. 24.1Gerstley Borate............. 13.8Wollastonite................ 5.8Magnesium Carbonate......... 2.5Barium Carbonate............08.6FRIT 3134................... 8.7FRIT 3195................... 2.3EPK Kaolin.................. 9.9Silica...................... 24.2Rutile...................... 8.0red iron oxide.............. 1.0 I'm working on a newer version of this glaze so the problem could fix itself. I'll do a test on it this week. Custer Feldspar............. 25.17Gerstley Borate............. 17.70Magnesium Carbonate......... 2.61Barium Carbonate............ 4.29FRIT 3134................... 9.09EPK Kaolin.................. 10.34Silica...................... 30.80Rutile...................... 8.00red iron oxide.............. 1.00 Link to comment Share on other sites More sharing options...
hershey8 Posted October 26, 2013 Report Share Posted October 26, 2013 I have two commercial cone 6 glazes that have laid around and settled/dried up some. I've mixed them up, but they crack after being applied to bisque. They seem to have adequate water. Can anything be done to correct this? Link to comment Share on other sites More sharing options...
Mart Posted October 27, 2013 Report Share Posted October 27, 2013 ....The problem is worse when it is put over another glaze....We have few glazes that are "clay based" and they do not like frit based glazes when applied to bisque ware... or was it the other way around. Link to comment Share on other sites More sharing options...
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