Rodders Posted January 8 Report Share Posted January 8 (edited) Hi, I am stumped. Can anyone help? I'm trying to mix Old Forge Floating Blue Nepheline Syenite 35.00 Gillespie Borate 23.50 Silica 23.00 EP Kaolin 11.00 Whiting 4.50 Strontium Carbonate 3.00 Rutile 4.00 Manganese Dioxide 2.00 Bentonite 2.00 Cobalt Carbonate 1.00 I was aiming for 1.42 SG so added about 85% water by weight. The resulting mix seemed very viscous; it was quite difficult to sieve, but the SG was spot on. I dipped a couple of test tiles; as I anticipated the glaze went on very thick, took longer to dry than usual, and had fine visible cracks, even with quite short dips. I tried testing the viscosity using a Ford cup, but the glaze was so thick that it did not all drain from the cup, invalidating the results. I therefore added some sodium silicate to deflocculate. There were no visible improvements. I came back to the glaze a few hours and it had separated with a thin layer of water on top and had started to gel. I remixed and added more sodium silicate, but the mix continued to gel getting thicker rather than thinner. I retested the SG; still 1.42. The consistency is like whipped cream. I have not fired the test tiles yet, but there seems little point as the mix is unusable as it is. Anyone got any suggestions? Edited January 8 by Rodders Quote Link to comment Share on other sites More sharing options...
Dick White Posted January 8 Report Share Posted January 8 (edited) When defloculating with sodium silicate, a funny thing happens if you go too far. It begins to thicken rather than get even thinner as you would expect. And you add more and it gets worse. Solving the problem requires understanding how defloculation occurs. The clay particles are sensitive to the acidity or alkalinity of the water. If the glaze slurry is too loose and separating quickly, a small dose of an acid, such as epsom salts or vinegar will flocculate it. If the glaze slurry is too thick, a small dose of an alkaline, such as sodium silicate or soda ash, will deflocculate it. But, as mentioned, if you deflocculate with too much sodium silicate, it starts gelling. Because the underlying problem is too much alkalinity, you just need to neutralize it with some acid. It seems crazy to flocculate this glaze that has gotten too thick from over defloculation, but that is what you need to do. Scoop out some and try it with a few drops of saturated epsom salts solution or vinegar. p.s., in your recipe, did you mean manganese dioxide instead of magnesium dioxide? Edited January 8 by Dick White Rodders and Rae Reich 2 Quote Link to comment Share on other sites More sharing options...
Rodders Posted January 8 Author Report Share Posted January 8 Ah, yes, I meant Manganese. Thanks for your suggestion Dick, I'll give it a try and report back. I'd like to sort this batch out of academic interest at least, although there is a significant chance it is heading towards the trash bin. Quote Link to comment Share on other sites More sharing options...
Callie Beller Diesel Posted January 8 Report Share Posted January 8 As a general rule, mixing gerstley borate and bentonite is a bad idea because it creates this situation. Enough Gerstley can deflocculate or even gel a glaze under its own power, and bentonite will make the effect worse. Add in Neph Sye, which can also be soluble, and it’s not super surprising this is happening. I haven’t done any tests with Gillespie to say if it does something similar to GB in the bucket or not, but I’m going to guess you’re finding it does. If you mix this glaze again, try it without the bentonite. There’s enough clay to keep it suspended without. Another thing worth checking is how long you’re mixing your glaze. Mixing factors heavily in Joe’s glaze process, as he uses a stick blender for tests, and he’s written blog posts about how that changes his results. I’m working with another of Joe’s recipes right now that someone else put together. We’re finding the bucket does loosen up significantly with a good 3+minutes with a drill mixer. Bill Kielb and Rae Reich 2 Quote Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted January 8 Report Share Posted January 8 (edited) Gillespie is even worse than gerstley for gelling glaze. I say keep adding more sodium silicate for the academic exercise and find a way to use a frit instead of Gillespie Borate going forward. There's nothing that is an exact swap so you would have to do a bit of testing and rejigging of ratios. Edited January 8 by High Bridge Pottery Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted January 8 Report Share Posted January 8 10 hours ago, Rodders said: I was aiming for 1.42 SG so added about 85% water by weight. Just a thought- You may want to set you SG first for what works best with the particular glaze ( Not necessarily a predetermined number) from there you may be able to adjust viscosity as needed to improve performance. Quote Link to comment Share on other sites More sharing options...
Rodders Posted January 8 Author Report Share Posted January 8 Thanks Bill; I was aiming to do that. 1.42 was recommemended for this glaze so that it why I was intending to start there. Bill Kielb 1 Quote Link to comment Share on other sites More sharing options...
Rodders Posted January 8 Author Report Share Posted January 8 There is a very good explanation of the effect Dick reminded me of on Digital Fire https://digitalfire.com/article/deflocculants%3A+a+detailed+overview. Clearly, when I thought the glaze was too viscous, it was already past the point on the graph when adding a deflocculant would reduce rather than increase the viscosity. I couldn’t understand how that could have been until I just retested my water supply and found it to be significantly alkaline. I live in a very hard water area, and the calcium and magnesium in hard water supplies causes it to be alkaline. Usually this is not a problem as I have a water softener, and my water is usually about pH 7.0, but on investigation it seems to have stopped working. Mystery solved. Bill Kielb, Kelly in AK and Rae Reich 3 Quote Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted January 9 Report Share Posted January 9 I would be surprised if you made it to the other side of the curve but hard to know how much some sodium silicate is. Quote Link to comment Share on other sites More sharing options...
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