Jennifer Baumeister on sun 19 dec 04
As a relative beginner to glaze making, I am starting to get a handle on it and become a little more adventuresome.
I tried a variation of MC6 High Cal Semi-mat 2 with Rutile 6, Copper carb 4, and Cobalt carb .5 ,
After mixing and screening 3 times and letting sit 24 hours. Made test and glazed a few small items, It turned out an absolutely beautiful variegated green. I was so excited to have such a successful start. The glaze was wonderful on white, red, and buff clay bodies.
The problem arose about 2 weeks later when I did the next firing. This glaze seemed to have gone a little bit watery
compared to the first time I used it. The suspension in the bucket was not holding well ( had to keep mixing for each dip ).
The glaze did not perform the same way at all, it came out of the kiln very dry looking light bluish gray with runny looking streaks of glossier and greener splotches.
My questions are :
Why did this happen ?
Will 2% bentonite fix the glaze ? ( or is there something else I can do to replicate the original )
Thanks,
Jen
PS. I am looking for a cone 6 red glaze that I can use to line coffee cups..does anyone have a recommendation.
John Hesselberth on sun 19 dec 04
On Sunday, December 19, 2004, at 10:18 AM, Jennifer Baumeister wrote:
> The problem arose about 2 weeks later when I did the next firing. This
> glaze seemed to have gone a little bit watery
> compared to the first time I used it. The suspension in the bucket was
> not holding well ( had to keep mixing for each dip ).
> The glaze did not perform the same way at all, it came out of the kiln
> very dry looking light bluish gray with runny looking streaks of
> glossier and greener splotches.
Hi Jen,
I can only guess, but I suspect your second applications were too thin.
As to the glaze suspension being less stable in the bucket, did you
rescreen it a time or two before you used it? I find that to be a good
idea after letting a glaze sit a while for a couple reasons. First it
does help with suspension stability. But second it assures that you
really are getting all the stuff in the bottom of your storage
container back into suspension. Just stirring or shaking will often not
accomplish that and you never really see what is left on the bottom of
the bucket when you just stir or shake. When you put it through a sieve
you can see what is left on the bottom of the bucket and make sure you
get it included.
Yes, a little (1-2%) bentonite will help with suspension stability;
however you have to take special care to put bentonite into an
already-mixed glaze. Take an old blender and use it to make a
suspension of bentonite in water before adding it to your glaze. If you
just dump the dry bentonite into an already-mixed glaze you will likely
never get it dispersed.
I hope this helps.
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Kate Johnson on sun 19 dec 04
>
> Yes, a little (1-2%) bentonite will help with suspension stability;
> however you have to take special care to put bentonite into an
> already-mixed glaze. Take an old blender and use it to make a
> suspension of bentonite in water before adding it to your glaze. If you
> just dump the dry bentonite into an already-mixed glaze you will likely
> never get it dispersed.
Hi John...
Siiiigh...wish I'd read this, or remembered, BEFORE I just mixed my first
batch of completely home made glaze an hour or so ago.... Is it
possible to put the whole mess in an old blender the better to mix the
bentonite?
gracias,
Kate who learns through failures. Theoretically...*GG*
Jennifer Baumeister on mon 20 dec 04
Thank you to everyone who responded to my questions.
I'll give the fixits a try. Luckily I had only made a 1500 gram batch.
Are there certain material combinations that cause this phenomena ( deflocculated )?
I have used the MC6 High Cal semi mat base with other combinations and have not had this problem..
( I am assuming it has something to do with the copper )
Is there anyway to predict "fall out" using the unity data for any given recipe ?
Wishing everyone Happy Holidays ,
Jen
BRRRrrrrrrrrrrrrrrrrrr, It's - 25 ( yes, minus 25 C ) out there ( Montreal, Canada )
.....just thought I'd share with all you southern folk wishing for a white Christmas.
.
Ron Roy on wed 22 dec 04
Hi Jen,
I did not respond to your original post because I knew John would have
better advice - he works at cone 6 and I work at cone 10 - so he has the
experience.
If a glaze has too much water - it will settle out quickly - as John said -
I would take some water off and try it thicker.
Neph Sy can make glazes settle out quickly - but in this case there is only
4% and the raw clay is high - so I would not expect the problem.
If - however - the water you are using is acidic - then I would think
deflocculation might be a problem - and bentonite will help. You may want
to use deionized water (or distilled) next time you mix this glaze
The advice about Epsom salts is also worth exploring - just melt a couple
of table spoons in a cup of water - make sure it's dissolved - a microwave
is a fast way to do it - just keep applying the heat till you can't see any
more crystals - but don't let it boil over.
Lets say you have a 5 gallon bucket of glaze - add one teaspoon of Ephesian
solution - stir - wait for 10 min - stir again. If the glaze thickens a bit
that may be all you need - the trick is to add it a little at a time - too
much and the problem gets worse by the way.
It is possible that the copper carb is processed with other chemicals -
they may still be present - and may be causing the problem - if that is the
case you can try "washing" it before you use it - use hot water and the
copper oxide or carbonate to it - when it settles out pour off the water -
do that a couple of times - to just the right amount of copper called for
in the glaze - that will lower the amount of any problematic solubles in
the copper - you can then just add it to your glaze before sieving.
Let us know if any of the suggested solutions work - we can all learn from
your experiments.
RR
>Thank you to everyone who responded to my questions.
>I'll give the fixits a try. Luckily I had only made a 1500 gram batch.
>
>Are there certain material combinations that cause this phenomena (
>deflocculated )?
>
>I have used the MC6 High Cal semi mat base with other combinations and
>have not had this problem..
>( I am assuming it has something to do with the copper )
>
>Is there anyway to predict "fall out" using the unity data for any given
>recipe ?
>
>Wishing everyone Happy Holidays ,
>Jen
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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