jrgpots Posted June 11, 2017 Report Share Posted June 11, 2017 If you have a ball mill, try ball milling your copper carbonate before adding it to the glaze or ball mill the dry glaze before adding water. It may help keep the copper carbonate in suspension. Jed Link to comment Share on other sites More sharing options...
glazenerd Posted June 11, 2017 Report Share Posted June 11, 2017 Lt: I am proposing a test with the alumina, not a solution. If the dispersement of color is uniform after the alumina test: then we know it is too fluid and adjustments to the recipe, or firing cycle; or both are needed. Just a quick way to narrow down the window of possibles. I think mea is on the right track, although I have seen this before in fritted ( fluid) recipes.) clay additions would be a fix: just have to figure out the cause. Nerd Link to comment Share on other sites More sharing options...
glazenerd Posted June 27, 2017 Report Share Posted June 27, 2017 Hi OldLady, both of your packages came today. So I looked at everything under the microscope first: all I need to do at this point, plenty of evidence. Two major things going on, with a secondary issue as well. You can see the differences in glaze thickness is this shot: the first sign that this glaze is over fired. The good news, your clay body is highly vitrified. (see glassy nodules reflecting?) In fact, the glaze is so hot that it is boiling. This is not silica issues, this is a way too hot issue. I looked at most of your samples, this is uniform across all of them. The cracking in your clay is not from forming, or from over firing: but rather from rapid drying. (note sodium deposit just above crack- white area) The white splotches are sodium crystals that have formed in the raw sample you sent me. In fact this clay body has an excessive amount of sodium spar in it: it tested at 9.22PH: which is nearly 0.75 over a normal cone 6 sodium specimen. I will be nice and not give the clay name..this time. Yes, sodium spar has dramatic effects on clay bodies:: drying/cracking is just one of many. Nerd Solution: you need a clay body with less sodium and more alumina: the other issue ( not enough alumina in the clay body) This body needs 20-30F less heat or much less soak time. Link to comment Share on other sites More sharing options...
glazenerd Posted June 27, 2017 Report Share Posted June 27, 2017 Lady: Do you mind if I hijack your thread to discuss clay and glaze issue more in depth? Nerd Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted June 27, 2017 Report Share Posted June 27, 2017 I agree with thickness being the culprit but not sure about it being too fluid/hot or anything like that. Looks pretty stable to me and the light blue in the first picture seems to have the same if less obvious issue. How did you extrapolate from the varying thickness to it being fluid or overfired? I will keep quiet about silica. Link to comment Share on other sites More sharing options...
glazenerd Posted June 27, 2017 Report Share Posted June 27, 2017 Joel: The same glaze thickness variations occur on the flat surfaces as well; just not shown here. The basic fact that this clay body has roughly 20% more sodium spar than required is the biggest indicator. You can see sodium crystals in the unfired raw sample ( white splotches) just above the crack, you can also see large white patches after firing. High levels of potassium will discolor the clay to a tan color and cause blisters/ pinholes in the glaze surface. Sodium also off gasses if saturated, but show up as micro bubbles. In my sodium testing ( still ongoing), the above is what I have seen most. The mere fact that the PH of 9.22 is the most revealing: a very hot batch of clay. PH is hard to grasp for most people: a PH of 9.00 is 100 times more potent than a PH of 8.00. A typical cone 6 sodium based clay should run in the 8.50 range or so, so this body at 9.22 is seriously over fluxed. So the off gassing sodium is creating the boiling seen in the picture. Remember also that glaze leaches materials from the clay: in this case a lot of sodium and little alumina. If alumina levels were higher, the glaze would not thin so much. Nerd Link to comment Share on other sites More sharing options...
oldlady Posted June 28, 2017 Author Report Share Posted June 28, 2017 nerd, thank you for the analysis. i love that clay. i do not want to think about trying to find a different one. i love that clay. it does just what i want it to do. i love that clay. this is going to take awhile to accept. i love that clay. i have to take time to adjust to thinking of my clay as less than perfect. i love that clay. how do i accept this idea. i love that clay. it is the fifth or sixth one i have tried and i love that clay. what can i do????????????? i am in shock.................................. Link to comment Share on other sites More sharing options...
Pugaboo Posted June 28, 2017 Report Share Posted June 28, 2017 I agree with you Oldlady... I LOVE THAT CLAY TOO. sob... to find out your perfect clay isn't so perfect is hard to accept... maybe we can just pretend it isn't so... maybe? Nerd tell us it isn't hopeless! Tell us there is hope! Sniffle ... holding a bag of my precious perfect clay close to me so it knows I still think it's perfect no matter what anyone else thinks. Yes I think you are perfect yes I know you make beautiful pieces yes I know you are a dream to decorate... yes yes yes. T Link to comment Share on other sites More sharing options...
glazenerd Posted June 28, 2017 Report Share Posted June 28, 2017 "also sodium-rich. These regions are probably small inclusions of unreacted sodium sulfate that became trapped as the glass solidified during cooling". From the National Laboratory study of sodium sulfide thermal decomposition. Joel: stoneware has sulfur (sulfates): which interact with sodium to form sodium sulfate. Pottery already knows the issues of sulfur in clay bodies. So I am reasonably certain the bubbles are sodium sulfate gasses escaping. Look closely at the bubbles pic: you can see white dots here and there: ( bare clay). Lady / Terry.. Did not mean to rain on your parade. The obvious is to fire a 1/2 cone lower to start. These are micro bubbles not readily obvious to the naked eye. I would imagine some would be visible pending darker colorants. This body is closer to a tan earthenware than it is stoneware. Looks like 8-10% Roseville fire clay! imco 400 perhaps, 15% ball clay and way way too much sodium. Been working on a spritz for finished pieces to retard drying time..working on it.. Nerd Link to comment Share on other sites More sharing options...
Min Posted June 28, 2017 Report Share Posted June 28, 2017 hmmmm, how would you explain the fact that Lady's and Terry's other glazes are fine on this claybody? Even the same base but without colourants or with cobalt are not creating problems? With all due respect, even though the claybody might not be all that it should be and possibly overfired, think this is mostly application and glaze suspension problems. Link to comment Share on other sites More sharing options...
glazenerd Posted June 28, 2017 Report Share Posted June 28, 2017 I found her glaze application to be nearly perfect. Copper melts at 1785F and cobalt at 2724F. Copper is processed from copper sulfide, yet another form of sulfur that reacts with sodium. This body could easily be fired a 1/2 cone lower with no adverse effects. Or Lady could simply reduce the KnaO levels in her copper glaze. Link to comment Share on other sites More sharing options...
bciskepottery Posted June 28, 2017 Report Share Posted June 28, 2017 I've been using Little Loafers for years; fires to an ivory/off-white, hardly a "tan stoneware". I've not had Old Lady's glaze problem. Link to comment Share on other sites More sharing options...
Min Posted June 28, 2017 Report Share Posted June 28, 2017 "Copper melts at 1785F and cobalt at 2724F" Cobalt has a high melting temp, agreed, but it readily dissolves in glazes. Try and keep a crisp line when using cobalt with brushwork decoration, you get a blurry, runny line especially with high boron and alkaline glazes. Still would slightly increase the epk to offset the running from the copper overfluxing the glaze. Another thing I noticed when looking at Lady's pics again is how the colour evens out on the level surfaces when the piece is reglazed, granted it has pooled more in the recessed areas but considering this is a second firing that would be a given. Link to comment Share on other sites More sharing options...
glazenerd Posted June 28, 2017 Report Share Posted June 28, 2017 There is an unknown in this equation: I have a sample bag of copper that I need to inspect. From visual glance: predates modern milling techniques: making it susceptible to higher sulfate content. This could be just a hot batch of clay as well, and not the norm. Link to comment Share on other sites More sharing options...
glazenerd Posted June 28, 2017 Report Share Posted June 28, 2017 Ok OldLady.. you asked "what is going on here?" So this is my final diagnosis. I broke open several other samples to find what is shown above: sodium deposits. I took a dropper of oxalic acid to test it: and it foamed (hydrogen gas) violently: so no doubt these deposits are sodium. However, this particular view is partly crystallization, but also partly poorly blended: IMO. I then did a slide of your copper carbonate sample: not liking what I see here either. Those black spots are carbons (sulfur), which I confirmed by subjecting the sample to acid test. The copper quickly separated out and stayed in suspension: but a fair amount turned black and settled to the bottom of the container. Which means your copper carbonate has a fair amount of sulfur (carbons) in it; which just compounds the problem even further. Sodium + sulfur = sodium sulfate gas: hence even more bubbles in your glaze. You have some clay that is 1. been poorly mixed as evidenced by the deposits shown above. 2. Has an excessive amount of sodium. The bubbles are off gassing sodium, combined with sulfur. Compounded even further from a fairly impure batch of copper carb. A bit of science thrown in: the term is: phase transition. As the sodium begins to melt. it changes from a solid to a gas (phase change). As the gas builds, the melting of other ingredients begin to occur. However, because of the high level of sodium, compounded by areas where it was never throughly mixed: gases came up through the clay, and acted as a flux in the copper: making it hyper-fluid. Copper - sodium- and sulfur have a particular chemical reaction not found with other transitional metals. So lets call it: "The Perfect Storm." psssstt... replace your copper carb supply... this is dirty stuff. I will write the clay off as poor mixing this time around. Nerd Link to comment Share on other sites More sharing options...
Guest JBaymore Posted June 28, 2017 Report Share Posted June 28, 2017 You have some clay that is 1. been poorly mixed as evidenced by the deposits shown above. 2. Has an excessive amount of sodium. The bubbles are off gassing sodium, combined with sulfur. Compounded even further from a fairly impure batch of copper carb. Fr om what I've seen around, many cone 6 clay body recipes are simply basic cone 9-1 0 bodies loaded with nepheline syenite. They use the higher soda content (than a true feldspar) to drop the maturity (as one might attempt to do in a glaze) since higher potash mostly insoluble sources are pretty non-existent. Because neph sy is slightly soluble in water (rate dependent on the ph) ........you get soluble sodium compounds into the water in the clay. Causes lots of issues.... like a bit of thixotropy-ish behavior in the plastic body if stored wet a long time, a tendency to hardpan in soaking reclaim, and stuff like you are seeing here in the drying and firing. best, ...............john Link to comment Share on other sites More sharing options...
neilestrick Posted June 28, 2017 Report Share Posted June 28, 2017 hmmmm, how would you explain the fact that Lady's and Terry's other glazes are fine on this claybody? Even the same base but without colourants or with cobalt are not creating problems? With all due respect, even though the claybody might not be all that it should be and possibly overfired, think this is mostly application and glaze suspension problems. I agree. Of course the glaze is going to vary in thickness- it was sprayed, and it's runny. It may not be a perfect clay or a perfect glaze, but the large thin areas were not from the glaze running- they just don't move like that. It was sprayed too thin in those areas. Link to comment Share on other sites More sharing options...
glazenerd Posted June 28, 2017 Report Share Posted June 28, 2017 John: When you put glaze on basically a flux biscuit: should not expect normal behaviors. Nerd Link to comment Share on other sites More sharing options...
Pieter Mostert Posted June 29, 2017 Report Share Posted June 29, 2017 It should be easy enough to test what effect the clay is having. Make two large test tiles, one from Little Loafers and one from a well-mixed low-sodium clay, and place them side-by-side when you spray the glaze on. Link to comment Share on other sites More sharing options...
glazenerd Posted June 29, 2017 Report Share Posted June 29, 2017 Peter: This is America: land of I want $1 dollar clay for 25¢. Nep Sy is .06¢ a lb in bulk wholesale: so it has become the flux of choice in clay bodies. Potassium is 4-5 times that. The only low sodium clay I am aware of is mine: which is a no sodium clay. I sent Old Lady a sample to play with, and asked her specifically to test her recipe on it. We shall find out soon enough. Nerd Link to comment Share on other sites More sharing options...
Pieter Mostert Posted June 29, 2017 Report Share Posted June 29, 2017 Peter: This is America: land of I want $1 dollar clay for 25¢. Nep Sy is .06¢ a lb in bulk wholesale: so it has become the flux of choice in clay bodies. Potassium is 4-5 times that. The only low sodium clay I am aware of is mine: which is a no sodium clay. I sent Old Lady a sample to play with, and asked her specifically to test her recipe on it. We shall find out soon enough. Nerd I'm surprised at the price difference. My local supplier sells 1kg of Neph Sy for about 50% more than 1kg of Potspar. Must be international vs local sources. Link to comment Share on other sites More sharing options...
Guest JBaymore Posted June 29, 2017 Report Share Posted June 29, 2017 Peter: This is America: land of I want $1 dollar clay for 25¢. Nep Sy is .06¢ a lb in bulk wholesale: so it has become the flux of choice in clay bodies. Potassium is 4-5 times that. The only low sodium clay I am aware of is mine: which is a no sodium clay. I sent Old Lady a sample to play with, and asked her specifically to test her recipe on it. We shall find out soon enough. Nerd I'm surprised at the price difference. My local supplier sells 1kg of Neph Sy for about 50% more than 1kg of Potspar. Must be international vs local sources. Some of this might be "supply and demand" aspects... with the key being "demand". Nepheline syenite is "THE" ground-up rock for most people (outside of Japan) pursuing the 'Holy Grail' of shino. The more "Japanese" people want that shino to look... the more the go-to rock is neph sy. So....... potters WANT it. So.... charge more for it. There is no other close source readily available. That it is a really cheap raw material on the "bulk" wholesale market is not something most studio artists are aware about. Most are buying from middlemen. best, ..................john Link to comment Share on other sites More sharing options...
glazenerd Posted June 29, 2017 Report Share Posted June 29, 2017 Actually, two middle men: Laguna, then your supplier. Link to comment Share on other sites More sharing options...
neilestrick Posted June 30, 2017 Report Share Posted June 30, 2017 Actually, two middle men: Laguna, then your supplier. You have to buy Neph Sye from Laguna? I think anyone who buys it in volume for clay mixing probably gets it directly from Unimin by the truckload. Link to comment Share on other sites More sharing options...
glazenerd Posted June 30, 2017 Report Share Posted June 30, 2017 Neil: was only commenting on traditional sources. I do not use Laguna for much of anything. Link to comment Share on other sites More sharing options...
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