John Britt on fri 23 aug 02
Kim,
Too much bentonite may cause your glaze to crawl. (It looks like you have
added about 6%.)
That is because it has absorbed a lot of water and has to shrink when the
water leaves.
Also, remember that when you add bentonite you are not just getting a
suspending agent, (one property of bentonite), you are also adding silica,
alumina, etc. So it will effect your glaze.
I would probably try to add another batch without the bentonite and figure
it out so that you will have the right amount in the final batch.
Hope it helps,
John Britt
Penland Clay
Kim Marie on fri 23 aug 02
I didn't realize till I was through that I think I accidentally put too much
bentonite in a 7650grms glaze batch. Should have been 325...think I put in
500. (I only had enough colorant to make the smaller batch.) I know
bentonite is mainly a suspension agent. If I leave the glaze as is do you
think this will create a problem?
Kim Marie
Spafford NY Where we're finally getting a break from a heat wave. How do
all y'all Texans take heat like this all the time?!??!?? Seein' how the
CNN weather map always shows the tip of Texas as a charred orangey black tip
tickling Mexico!!!!!
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Snail Scott on fri 23 aug 02
At 08:06 AM 8/23/02 -0400, you wrote:
>I didn't realize till I was through that I think I accidentally put too much
>bentonite...
Bentonite in larger quantities will have the opposite,
effect, causing particulates to drop out of suspension.
Bentonite is used for this purpose by winemakers, to
clarify. It depends on the amount of bentonite you've
got in it. Above 3% is potentially a problem.
-Snail
Gavin Stairs on fri 23 aug 02
At 07:25 AM 23/08/2002 -0700, Snail wrote:
>Bentonite in larger quantities will have the opposite,
>effect, causing particulates to drop out of suspension.
>Bentonite is used for this purpose by winemakers, to
>clarify. It depends on the amount of bentonite you've
>got in it. Above 3% is potentially a problem.
I don't think this is quite right. The use of sodium silicate and
bentonite as a clarifier works this way.
The coagulant or flocculant is put in the wine in very slight
concentrations. Egg whites can be used. Remember, what ever is used must
be food grade. This makes the minute particles attract each other slightly.
Then the flocculated batch is mixed with a filter medium, the purpose of
which is to keep the filtration mat permeable as it thickens during
filtration. Bentonite can be used for this, also sawdust and other
things. Again, it must be food grade if the product being clarified is
wine. The filtration medium accumulates on the filter, and rapidly it
becomes the filter itself. The coagulated particles get trapped in the
filter mat, and don't get through.
Bentonite is used in glazes as a suspension agent. It is doing much the
same job it was doing in the filtration mat, except in glazes it is
entrapping the glaze particles to prevent them from going out of suspension.
The problem of too much bentonite, or CMC, or wallpaper paste, or Material
A, is that they absorb lots of water, and expand, and when the piece is
dried, you'll get a lot of shrinkage. So too much of it is not a good
thing. The querent will know if she had too much bentonite if the glaze
flakes off the pot.
Gavin
Ababi on sat 24 aug 02
I do not know what will happen. If you wrote what you had done, you could give it a
chance, fire it on a test tile, might love it!
Ababi
---------- Original Message ----------
>At 07:25 AM 23/08/2002 -0700, Snail wrote:
>>Bentonite in larger quantities will have the opposite,
>>effect, causing particulates to drop out of suspension.
>>Bentonite is used for this purpose by winemakers, to
>>clarify. It depends on the amount of bentonite you've
>>got in it. Above 3% is potentially a problem.
>I don't think this is quite right. The use of sodium silicate and
>bentonite as a clarifier works this way.
>The coagulant or flocculant is put in the wine in very slight
>concentrations. Egg whites can be used. Remember, what ever is used must
>be food grade. This makes the minute particles attract each other slightly.
>Then the flocculated batch is mixed with a filter medium, the purpose of
>which is to keep the filtration mat permeable as it thickens during
>filtration. Bentonite can be used for this, also sawdust and other
>things. Again, it must be food grade if the product being clarified is
>wine. The filtration medium accumulates on the filter, and rapidly it
>becomes the filter itself. The coagulated particles get trapped in the
>filter mat, and don't get through.
>Bentonite is used in glazes as a suspension agent. It is doing much the
>same job it was doing in the filtration mat, except in glazes it is
>entrapping the glaze particles to prevent them from going out of suspension.
>The problem of too much bentonite, or CMC, or wallpaper paste, or Material
>A, is that they absorb lots of water, and expand, and when the piece is
>dried, you'll get a lot of shrinkage. So too much of it is not a good
>thing. The querent will know if she had too much bentonite if the glaze
>flakes off the pot.
>Gavin
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