Carole Fox on sat 7 apr 07
I added 2% bentonite to a 10 lb. batch of dry glaze, and when I mixed the
glaze with the appropriate amount of water, it turned as thick as
pudding. The last time I mixed this glaze, I did not add any bentonite,
and it kept settling out and eventually hard-panned. The question now is
how to get the thick batch to a reasonable consistency without diluting
excessively with water. I suppose I could mix another 10 lb. batch
without the bentonite and blend the two, but I really don't need this much
glaze, and I'm not sure what the result would be. Any suggestions would
be greatly appreciated.
Carole Fox
Dayton, OH
Richard Aerni on sat 7 apr 07
Carole,
It seems unlikely that 2% of bentonite would cause your glaze to go
pudding-like, but try to add a couple of tablespoons of Darvon 7 to the
glaze to deflocculate it. I have a couple of other deflocculants at the
studio that I sometimes use, but the chemical names escape me right now
(long day in the studio) and I will forward them to you after my session
there on Sunday.
Best,
Richard Aerni
Rochester, NY
John Rodgers on sat 7 apr 07
Carole,
You might try the tiniest bit of sodium silicate to see if that loosens
the glaze up. Cut the silicate to 50/50 water to silicate, then add only
a few drops at a time. The shift will happen quickly.
Once liquid again, I suggest you adjust the glaze density to 1.5 with
water.
Regards,
John Rodgers
Chelsea, AL
Carole Fox wrote:
> I added 2% bentonite to a 10 lb. batch of dry glaze, and when I mixed the
> glaze with the appropriate amount of water, it turned as thick as
> pudding. The last time I mixed this glaze, I did not add any bentonite,
> and it kept settling out and eventually hard-panned. The question now is
> how to get the thick batch to a reasonable consistency without diluting
> excessively with water. I suppose I could mix another 10 lb. batch
> without the bentonite and blend the two, but I really don't need this much
> glaze, and I'm not sure what the result would be. Any suggestions would
> be greatly appreciated.
>
> Carole Fox
> Dayton, OH
>
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Joseph Herbert on sun 8 apr 07
I actually don't know if this will help but, in the oil field the "yield" of
bentonite in drilling mud is increased by raising (make more base) the pH.
Mud mixers add pearl ash (potassium hydroxide) to the mud to make it thicker
for the amount of bentonite added. You might try adding some acid, like
vinegar or oxalic acid, to a sample to see if there is a thinning effect. I
think it is probably best to use organic acids to avoid adding materials
that could affect the glaze. Nitric Acid could work but using strong acids,
like this or Hydrochloric, is a rather dangerous activity. You can get pH
test strips at a swimming pool supplier.
It is quite possible that this won't work. Much of the way that bentonite
acts is a physical reaction in which water is attracted to the clay
platelets by electrical attractions.
Another possibility is to try to defeat the thixothropic properties of the
slurry by continuously vibrating it. Thixothropic slurries tend to set up
or "gel" when stationary. Constant stirring or vibration can defeat the
thickness to a certain extent. Think of the ketchup bottle, once the
viscosity of thixothropy is broken, the fluid flows rather well.
Joseph Herbert
Joseph Herbert
Technical Writer
Irving, Texas
214-725-8305 (Cell)
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