Ron Collins on sun 8 dec 02
Does bentonite in any way, as an addition to the base glaze , in amounts =
of approximately one percent, in any way change the melting point of the =
glaze, theoretically? I know there are many variables, but I am always =
hesitant to put in some, when not tested, or called for, because it is =
refractory (?) and I don't want a higher melting temp than I already =
have with any glaze. In general, just in general, can one add bentonite =
for a little suspension, without too much concern? Melinda Collins, =
Antigua, Guatemala
David Beumee on mon 9 dec 02
12/8/02 5:53:27 PM, Ron Collins wrote:
>Does bentonite in any way, as an addition to the base glaze , in amounts of approximately one percent, in any
way change the melting point of the glaze, theoretically? I know there are many variables, but I am always
hesitant to put in some, when not tested, or called for, because it is refractory (?) and I don't want a higher melting
temp than I already have with any glaze. In general, just in general, can one add bentonite for a little suspension,
without too much concern? Melinda Collins, Antigua, Guatemala
>
Especially in glazes that contain no clay, bentonite is very useful in keeping a glaze in suspension. You
can add a percent or two without fear of raising the melting point of your glaze. It's often useful to add the
bentonite to another dry ingredient before putting it in water.
David Beumee
Earth Alchemy Pottery
Lafayette, CO
USA
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Paul Lewing on mon 9 dec 02
on 12/8/02 4:53 PM, Ron Collins at Melron@CONEXION.COM.GT wrote:
> Does bentonite in any way, as an addition to the base glaze , in amounts =
> of approximately one percent, in any way change the melting point of the =
> glaze, theoretically?
No. In fact, with the exception of the colorants, you can add or subtract
1% of virtually any glaze material in any recipe and notice absolutely no
difference in the fired result. In fact, if you're working with a
calculation program and change a material by 1% either way, you often see no
change in the numbers, unless you've got it set to carry out calculations to
something ridiculous like three decimal places.
However, an addition of 1% bentonite can significantly alter how well a
glaze stays in suspension in the water.
Paul Lewing, Seattle
iandol on tue 10 dec 02
Dear Melinda,
I would expect that additions of Bentonite would have no effect what so =
ever on the melting point of your glazes. Melting Point is controlled by =
your Felspars and Frits and Boron minerals. Bentonite would have an =
effect on the maturing temperature were it included in large quantities. =
But the idea of one per cent as an additive to ensure suspension, =
something I add my self once I get to the bucket stage, never seems to =
make any difference in comparison to the original test sample mixes =
which are made without it.
Good to know you are still working hard.
Best regards and Good Wishes for the Festive Season.
Ivor Lewis. Redhill, south Australia
Brant Palley NMCLAY.com on tue 10 dec 02
At cone 10 the Volclay brand bentonite fires (by itself) to a gloss black
glass,This can (above 1%)have an effect in a white or clear glaze on a
white clay.
The macaloid or veegum types(smectites)fire to a white dry surface.
It is always nice to fire all your glaze materials by themselves- make
little mounds or buttons and put them on a test tile, fire to the glaze
temp you work at. Some things may suprise you.
www.nmclay.com
Ron Roy on wed 11 dec 02
Hi Melinda,
I would not expect it to - it all depends on how well melted the glaze is
to start with - if it is on the verge of not melting it could have some
effect - it does add alumina.
When I compare bentonite with red art for instance I would expect the red
art to melt more at cone 6 than bentonite but I also would expect the
bentonite to be well sintered at cone 6.
Part of the intelligent answer to this question would be - it depends on
what cone you are firing to - at cone 10 it would have less effect than at
cone 6.
Perhaps a few tests are what you need to convince you about this.
The three ways to stop a glaze from settling out to fast or two hard are.
1. Change the Kaolin to ball - but do it with calculation software to make
sure the alumina and silica are the same.
2. Add bentonite - up to 2%
3. Add Epsom salts
If none of those work - and your bisque is not low fired - it's time to
reformulate - to take out whatever material is leaching sodium into the
glaze - defloccing it - and replace it with a less soluble source. And/or -
take out a material which is supplying alumina so you can get more raw clay
in the recipe - subbing 3134 for 3124 for instance - using calculation
software of course to maintain the molecular proportions.
Sounds very complicated but I don't find it so - I do a lot of this for
potters and I find it very straight forward - if you are looking at the
molecular representation of the fired glaze. I have to add - there are some
glazes that defy this methodology - a few unbalanced that are hopeless -
maybe 2 or 3%.
RR
>Does bentonite in any way, as an addition to the base glaze, in amounts of
>approximately one percent, in any way change the melting point of the
>glaze, theoretically? I know there are many variables, but I am always
>hesitant to put in some, when not tested, or called for, because it is
>refractory (?) and I don't want a higher melting temp than I already have
>with any glaze. In general, just in general, can one add bentonite for a
>little suspension, without too much concern? Melinda Collins, Antigua,
>Guatemala
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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