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.

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.

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.

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?