Rodders

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.

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.

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.

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?