davidh4976 Posted September 13, 2023 Report Share Posted September 13, 2023 I started working up some blue glazes by starting with a some good gloss clear glaze recipes I've used before and adding 1.5% cobalt carbonate. On the batches I've run, the fired glaze goes clear over edges. It looks great if that's what you want, but I'm looking for a blue glaze that stays blue even over edges/texture. I also want to avoid Gerstley Borate, Neph Sy, and Talc. GB because of end-of-production. Neph Sy because it somewhat contributes to hard panning. Talc because of recent quality. For cone 6 stoneware. Any ideas or suggestions? Quote Link to comment Share on other sites More sharing options...
Kelly in AK Posted September 13, 2023 Report Share Posted September 13, 2023 I expect people more knowledgeable than me will check in, but for my initial reaction, I suggest you’ll want to look into various boron based frits. They will give you some modicum of certainty, that is at least one of your glaze ingredients can be depended on to be exactly what the analysis says it is. You’ll get the boron content you need to flux things at cone6. I lean heavily on Ferro frits 3124 and 3134, but the are several others you can use to tune your glazes with specificity. As to blue at cone 6 my thought was including an opacifier (zircopax, tin) would help even things out and reduce that “breaking” quality. That’s just a guess. I have used a glaze from John Britt called “John’s Noxema” that fired very evenly. I didn’t like it for exactly the reason you might seek it: it didn’t break enough on edges and texture. Callie Beller Diesel and Rae Reich 2 Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted September 13, 2023 Report Share Posted September 13, 2023 3 hours ago, davidh4976 said: I started working up some blue glazes by starting with a some good gloss clear glaze recipes I've used before and adding 1.5% cobalt carbonate. On the batches I've run, the fired glaze goes clear over edges. It looks great if that's what you want, but I'm looking for a blue glaze that stays blue even over edges/texture. I also want to avoid Gerstley Borate, Neph Sy, and Talc. GB because of end-of-production. Neph Sy because it somewhat contributes to hard panning. Talc because of recent quality. For cone 6 stoneware. Any ideas or suggestions? What comes to mind is as a general rule 0.15 boron ought to get you a cone 6 melt regardless of source. And maybe search Glazy.org defining the characteristics and color you desire. (Example below) Kelly in AK 1 Quote Link to comment Share on other sites More sharing options...
davidh4976 Posted September 13, 2023 Author Report Share Posted September 13, 2023 I'm using Frit 3195 and it's breaking. I'll try John’s Noxema”. Thanks for the tip! I saw that in Britt's book, but it's so hard to tell if it's breaking by just looking at the photos. Same challenge with the glazes on glazy.org. Quote Link to comment Share on other sites More sharing options...
Hulk Posted September 13, 2023 Report Share Posted September 13, 2023 I'm using Lakeside Pottery Clear Blue; it goes on and fires well, does not move much, and is fairly consistent over edges. The formula is on Lakeside Pottery's website; it's been copied to Glazy as well: Clear Blue | Glazy It does call for Talc. I'm using the no longer widely available C-98 talc, and have enough to last several years, however, if/when the supply runs low, I'll be testing alternative sources of MgO, an important part of several glazes I use and really (really!) like... There's some lightening at the edge of the knob, which may be difficult to avoid with any transparent blue over white clay; any road, it lays flat and doesn't move, excepting if put on very thickly. Rae Reich 1 Quote Link to comment Share on other sites More sharing options...
Min Posted September 13, 2023 Report Share Posted September 13, 2023 You want to look for a stiff glaze (little glaze mobility / fluidity) if you don't want it to break on edges. Think of majolica type glazes, they are high in alumina making them a stiff non fluid glaze so when the overglaze brushwork is put on the designs don't run or move. If you don't want to use talc then try your hand with a glaze calculator tool, like the free one on Glazy, and have a go at removing the talc and supplying the now lost magnesium with dolomite instead. You will have to tinker with the amounts as it isn't a 1:1 swap then will need to rebalance the remaining oxides in the formula. I had a look at Tom's Lakeside Blue recipe above, couple thoughts about it. First thing that jumps out at me is the gum in it, I'm guessing it's there because the glaze might have a tendency to crawl without it due to the super high amount of epk. (Epk shrinks as it dries, excessive shrinkage = cracking which more often than not results in glaze crawling during the glaze fire). Bit of a band-aide solution to add gum when supplying part of the epk through calcined epk is simpler. Other thing is the colourants are included in the total, not as an addition. Makes it easier to adjust a recipe if the colourants are a separate addition from the main recipe. If possible I would reduce the cobalt, using less of a transition metal is preferable if the colour is still okay. I redid the original recipe first with just replacing the talc with dolomite to supply the magnesium. Then I took that recipe and replaced about half the epk with calcined epk. Glaze with the calcined epk is going to appear thinner in the bucket with the same amount of water. (measure specific gravity) I didn't include the gum in the recipe as it doesn't contribute to the fired chem. If you try this please just mix up a small test amount first as what looks good on paper doesn't always translate to a pot. dhPotter, Hulk and Callie Beller Diesel 3 Quote Link to comment Share on other sites More sharing options...
davidh4976 Posted September 13, 2023 Author Report Share Posted September 13, 2023 Min, thanks for the info! It's good to see someone else's work. Yes, I use the Insight tool and do 200mg test batches. I think I'll try your conversion with the calcined EPK in addition to John’s Noxema. I don't mind testing more than one version at a time and then selecting the one I like best. And, I always do tests that include crazing tests for our clays. Quote Link to comment Share on other sites More sharing options...
Min Posted September 13, 2023 Report Share Posted September 13, 2023 Is this the Noxema Blue recipe below? If it is the expansion is going to be super high from all that custer spar in it. It's unusual to see that much custer in a ^6 glaze. What might control the crazing from such a high COE glaze is the high amount of cobalt carb in it, which is another point, if it can be reduced without causing other issues that would be good. https://glazy.org/recipes/2475 Quote Link to comment Share on other sites More sharing options...
Kelly in AK Posted September 14, 2023 Report Share Posted September 14, 2023 I dug up “John’s Noxema,” it’s from John Britt’s book The Complete Guide to Mid Range Glazes. Some similarities, some differences. Lots of feldspar, but soda not potash. No wollastonite or Gerstley borate, rather strontium and 3134. An abundance of cobalt, for sure. Kona F-4 spar 50 Frit 3134 24 EPK 11 Strontium carb 11 Silica 4 Add: Cobalt carb 3 Bentonite 2 Min 1 Quote Link to comment Share on other sites More sharing options...
davidh4976 Posted September 14, 2023 Author Report Share Posted September 14, 2023 (edited) 1 hour ago, Min said: Is this the Noxema Blue recipe below? If it is the expansion is going to be super high from all that custer spar in it. It's unusual to see that much custer in a ^6 glaze. What might control the crazing from such a high COE glaze is the high amount of cobalt carb in it, which is another point, if it can be reduced without causing other issues that would be good. https://glazy.org/recipes/2475 No, that's different from John's Noxema (in John Britt's "The Complete Guide to Midrange Glazes). But, now that I put John's Noxema into Insight, it too has a high expansion and I would expect crazing on stoneware. Edited September 14, 2023 by davidh4976 Quote Link to comment Share on other sites More sharing options...
Min Posted September 14, 2023 Report Share Posted September 14, 2023 Thanks Kelly and David. Same principal applies though, really high spar. Sodium will be higher in the Noxema from Britt's book than the Custer one from Glazy but the COE is still going to be super high, would probably craze on most bodies without the cobalt carb. and might still craze even with the high 3.0 amount. Quote Link to comment Share on other sites More sharing options...
davidh4976 Posted September 14, 2023 Author Report Share Posted September 14, 2023 (edited) [I edited out my mistaken reply; don't know how to simply delete it.] Edited September 14, 2023 by davidh4976 Quote Link to comment Share on other sites More sharing options...
Min Posted September 14, 2023 Report Share Posted September 14, 2023 If you have a good blue already and just want to make it less fluid so it doesn't go clear on breaks try adding increments epk and silica in the ratio by weight of 1:1.25 epk to silica. ( to keep the silica:alumina ratio the same). There will be a point when the glaze is still melting well but won't be so runny. 200 base (include the cobalt) then add 2 epk + 2.5 silica dip a tile and repeat 2 or 3 times. Not super accurate and the cobalt will be diluted a bit but it will get you in the ballpark. akilpots and Kelly in AK 2 Quote Link to comment Share on other sites More sharing options...
Callie Beller Diesel Posted September 14, 2023 Report Share Posted September 14, 2023 Another avenue could be to add some zircopax to the recipe of your choice. Usually you don’t want it in a cobalt glaze because cobalt is pretty opaque by itself, but if you have a base glaze that works in all other respects, that could serve to get rid of any pooling. Quote Link to comment Share on other sites More sharing options...
davidh4976 Posted December 13, 2023 Author Report Share Posted December 13, 2023 I think I finally got a good blue that does not go thin on edges. I'm at the point of having also tested it for crazing on 3 of our 6 studio cone 6 clays. It looks pretty good. Here is what I ended up with. Now that Custer Feldspar is no longer being mined, I'll have to retest with Mahavir Feldspar. It looks like I'll have to add some more silica to get to the same chemistry. whiting 5.9 dolomite 5.2 custer feldspar 28.8 ferro frit 3134 14.2 epk 17.3 silica 26.4 cobalt carbonate 1.9 rutile 0.3 Hulk and Min 2 Quote Link to comment Share on other sites More sharing options...
Babs Posted December 13, 2023 Report Share Posted December 13, 2023 On 9/13/2023 at 11:40 PM, Hulk said: I'm using Lakeside Pottery Clear Blue; it goes on and fires well, does not move much, and is fairly consistent over edges. The formula is on Lakeside Pottery's website; it's been copied to Glazy as well: Clear Blue | Glazy It does call for Talc. I'm using the no longer widely available C-98 talc, and have enough to last several years, however, if/when the supply runs low, I'll be testing alternative sources of MgO, an important part of several glazes I use and really (really!) like... There's some lightening at the edge of the knob, which may be difficult to avoid with any transparent blue over white clay; any road, it lays flat and doesn't move, excepting if put on very thickly. Have you tried it without the CMC? Why is it included? Glaze application? Quote Link to comment Share on other sites More sharing options...
Hulk Posted December 14, 2023 Report Share Posted December 14, 2023 Hi Babs, No haven't tried Lakeside Pottery Clear Blue w/o CMC. Not sure why it's included; the notes don't mention anything about it. Next time mixing some up, I'll pour off some and withhold its CMC to do a side by side. My guess is the CMC is for keeping it stuck on. This blue is one of the recipes I'd selected when first making up a list of materials for glazes - was driving the truck to the big city, so. Any road, this blue and the red I use are somewhat translucent; I really like them. Quote Link to comment Share on other sites More sharing options...
davidh4976 Posted February 2 Author Report Share Posted February 2 After a bit of testing, I found a Cone 6 recipe that gives a good, deep blue color that stays blue even over edges/texture. I avoided Gerstley Borate, Neph Sy, and Talc. GB because of end-of-production. Neph Sy because it somewhat contributes to hard panning. Talc because of recent quality. This has been tested and found to be craze free (boiling water/ice water test) on the following clay bodies from our local supplier, New Mexico Clay: Marilyn's BOD, Ochre, E-Speckled, Cashmere, and Chocolate (these are all of the Cone 6 clay bodies that we now support in our pottery). On Chocolate, the glaze surface does not look as smooth as on the other four which look great. Here are the two recipe versions, one using Mahavir Feldspar and the other using G-200 Feldspar (because we have both in our supply!). AMT MATERIALS 27.6 MAHAVIR POTASH FELDSPAR 26.5 SILICA 325 15.3 FERRO FRIT 3134 18.4 EPK 12.2 DOLOMITE 2.0 COBALT CARBONATE 102.0 TOTAL AMT MATERIALS 29.3 G-200 FELDSPAR 26.2 SILICA 325 13.9 FERRO FRIT 3134 16.4 EPK 12.2 DOLOMITE 2.0 COBALT CARBONATE 100.0 TOTAL Min and Hulk 2 Quote Link to comment Share on other sites More sharing options...
Min Posted February 3 Report Share Posted February 3 @davidh4976, good job on subbing the Custer out. I like how much silica and alumina are in the formula, will make for a good durable glaze. I could see a bit of iron in the recipe if you ever wanted to tone down the blue a little. Callie Beller Diesel 1 Quote Link to comment Share on other sites More sharing options...
davidh4976 Posted February 3 Author Report Share Posted February 3 (edited) 32 minutes ago, Min said: @davidh4976, good job on subbing the Custer out. I like how much silica and alumina are in the formula, will make for a good durable glaze. I could see a bit of iron in the recipe if you ever wanted to tone down the blue a little. Thanks! Everyone in the pottery LOVES the color, so I am not tweaking the color at all! :-) I general, I am finding that Al2O3 of about 0.4 and SiO2 of about 3.5 (UMF) is working well for our "workhorse" cone 6 glazes. I may play with increasing the B2O3 flux a bit to see if I can get the glaze to smooth out on the Chocolate clay body without detrimentally impacting the color and coverage on the other clay bodies. Edited February 3 by davidh4976 Quote Link to comment Share on other sites More sharing options...
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