Lbegley Posted December 1, 2018 Report Share Posted December 1, 2018 I have a glaze that clumps even after being screened. After it sits and you stir it, little blobs remain and it isn’t a uniform dip. Heres the formula: Wollastonite 5.5 Custer feldspar 28.5 EPK. 28 silica. 15 dolomite. 19 Gerstley borate. 4 And, like all of the studio glazes I add some Epsom salts to keep it from settling. I’m wondering if I should leave it out of this one, or if there’s anything else I can do to keep from having to rescreen it all the time. Link to comment Share on other sites More sharing options...
liambesaw Posted December 1, 2018 Report Share Posted December 1, 2018 Epsom salts and Gerstley Borate are the only two things I see that would gum things up. That has enough clay to stay suspended. Link to comment Share on other sites More sharing options...
Mark C. Posted December 1, 2018 Report Share Posted December 1, 2018 That recipe is almost 1/3 clay so no epsom will be needed as it should float well. Are you mixing it with a power jiffy mixer? or a stick? is the screen 80 mesh? Link to comment Share on other sites More sharing options...
Lbegley Posted December 1, 2018 Author Report Share Posted December 1, 2018 This is in a community college studio and I use a jiffy mixer to make the glazed, but students use paddles to mix them (apparently before I got there a student drilled through the bottom of a bucket with the jiffy mixer and spilled 20 gallons of glaze, so they aren’t allowed to use it anymore!) I use a 80 mesh screen, but this glaze forms little soft globs that stay in suspension within a day. The lab tech that I replaced told me to toss a handful of epsom salt into each batch of glaze mixed so I’ve been following that tradition, but this is a new glaze and I will try it without next time. Link to comment Share on other sites More sharing options...
neilestrick Posted December 1, 2018 Report Share Posted December 1, 2018 What cone is this glaze? The formula is not great- quite high in alumina, overloaded with magnesium. I assume it's quite matte? I'd run some tests before eating off of it. Link to comment Share on other sites More sharing options...
Lbegley Posted December 1, 2018 Author Report Share Posted December 1, 2018 2 hours ago, neilestrick said: What cone is this glaze? The formula is not great- quite high in alumina, overloaded with magnesium. I assume it's quite matte? I'd run some tests before eating off of it. It’s a cone 10 glaze, matte. Aside from maybe staining what would make it a bad to eat off of? There are no colorants in the glaze. What sort of testing do you recommend? Link to comment Share on other sites More sharing options...
C.Banks Posted December 2, 2018 Report Share Posted December 2, 2018 fwiw, other than potassium + sodium, the recipe falls within the limts set out in Hyperglaze for a cone 10 matte Silica is a bit low though so it may craze a bit. Link to comment Share on other sites More sharing options...
C.Banks Posted December 2, 2018 Report Share Posted December 2, 2018 I took the liberty of fiddling a bit - hope you don't mind. I'm terrible for fixing things that may or may not need fixing. wollastonite 6.00 custer potash feldspar 23.00 epk 22.00 silica 26.00 dolomite 19.00 gerstley borate 4.00 According to hyperglaze this brings the silica up while not lowering the alumina too much. The rest stays about the same. This shifts the si:al ratio by a good margin but it still falls next to some other magnesia mattes I was working with. Link to comment Share on other sites More sharing options...
Lbegley Posted December 2, 2018 Author Report Share Posted December 2, 2018 Thanks C. Banks! I’ll test your adjusted glaze and see how it goes! Link to comment Share on other sites More sharing options...
Babs Posted December 2, 2018 Report Share Posted December 2, 2018 You haven' added white bentonite instead of dolomite??? Link to comment Share on other sites More sharing options...
Lbegley Posted December 2, 2018 Author Report Share Posted December 2, 2018 10 hours ago, Babs said: You haven' added white bentonite instead of dolomite??? Ha! I’m starting to think maybe I accidentally used cornstarch! It’s so gloopy and weird. Link to comment Share on other sites More sharing options...
Babs Posted December 2, 2018 Report Share Posted December 2, 2018 So no possibility of wrong ingredients?? I'd be making a small batch and seeing how that turned out ....... ..human error then or when decanting ingredients into bins have happened before Link to comment Share on other sites More sharing options...
Magnolia Mud Research Posted December 2, 2018 Report Share Posted December 2, 2018 I have been working on a cone 10 matte base glaze. Your recipe is similar to our clear glaze base with dolomite and extra EPK added and without the borate. Thanks for the recipe and test piece images; these data have provided me with a different direction to explore. Suggestion for troubleshooting: Separate the 'globs' from the glaze, and fire them separately on a test piece. also let the 'globs' dry and compare to the glaze ingredients. LT Link to comment Share on other sites More sharing options...
Lbegley Posted December 2, 2018 Author Report Share Posted December 2, 2018 2 hours ago, Babs said: So no possibility of wrong ingredients?? I'd be making a small batch and seeing how that turned out ....... ..human error then or when decanting ingredients into bins have happened before It’s always possible that I was off in my own imagination and screwed up the ingredients! But this is a busy community studio and it’s already been remixed a few times, and the glaze fires to be what we expect it to look like, so that seems unlikely. Link to comment Share on other sites More sharing options...
Lbegley Posted December 3, 2018 Author Report Share Posted December 3, 2018 2 hours ago, Magnolia Mud Research said: I have been working on a cone 10 matte base glaze. Your recipe is similar to our clear glaze base with dolomite and extra EPK added and without the borate. Thanks for the recipe and test piece images; these data have provided me with a different direction to explore. Suggestion for troubleshooting: Separate the 'globs' from the glaze, and fire them separately on a test piece. also let the 'globs' dry and compare to the glaze ingredients. LT Glad that the recipe is helpful to you! I’ll investigate the globs and see if they are some single ingredient precipitating out, or the mixed glaze coagulated. Thanks for the idea! Link to comment Share on other sites More sharing options...
curt Posted December 3, 2018 Report Share Posted December 3, 2018 As said earlier, smells like some unhelpful interaction between the Gerstley Borate, the Epsom salts, the relatively high clay content, and possibly even the chemistry of the water you are using. All that said, I would focus on the Gerstley Borate and the Epsom salts. Are you dissolving the Epsom salts in warm water before adding them? If not, could it be that chunks of epsom salt are providing the “seed” for the clumps? Maybe try dissolving the Epsom salt first and seeing if that helps. if not, maybe mix up a small batch with no Epsom salts and try adding a small incremental amount at a time and stirring, and observe gelling behaviour. If nothing happens try the same thing with the Gerstley Borate, i.e., mix the glaze without it, then add it in in small incremental amounts and see what happens. Link to comment Share on other sites More sharing options...
neilestrick Posted December 3, 2018 Report Share Posted December 3, 2018 On 12/1/2018 at 5:39 PM, Lbegley said: It’s a cone 10 glaze, matte. Aside from maybe staining what would make it a bad to eat off of? There are no colorants in the glaze. What sort of testing do you recommend? Hmmm. Not sure what happened there. I ran it again, and it's within limits like C. Banks said. My bad! I would do some acid tests, though, like lemon juice and /or vinegar to make sure it's durable. Link to comment Share on other sites More sharing options...
Mark C. Posted December 3, 2018 Report Share Posted December 3, 2018 Curt summed it up well the Epsom salts need to be dissolved in warm water other wise not can clump with other ingredients.I have seen this happen before. Link to comment Share on other sites More sharing options...
C.Banks Posted December 3, 2018 Report Share Posted December 3, 2018 On 12/1/2018 at 7:58 PM, Lbegley said: Thanks C. Banks! I’ll test your adjusted glaze and see how it goes! :) You're very welcome. I'll wager a stack of cermaic monthlies against that test settling. Link to comment Share on other sites More sharing options...
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