cHuCk on thu 21 sep 00
> cHuCk wrote:
>
> ...and watch out for high contents of Neph. Sy.
>
> Why Chuck?
>
> Diane, curious in CT
Mostly because I had read a post by Ron Roy that suggested that it was an
inconsistent material. I don't want to misquote him....but I remember he
thought more than 20 percent could start to cause some problems. (Please
correct me if I am out of line) I have been reading a lot on the Digital
Fire pages too. Just seems like it does not get used as much as it once did.
Whiting is another material that is best left for ground sweetener as it has
a lot of out gassing. It's better to get your CaCo in a material like
Wollastonite. This info came from Tony Hansen. I use Mason stains to color a
lot of our glazes and they recommend that there is CaCo in the glaze. I use
Whiting to supply it and he suggested that many of the big glaze companies
do not use it anymore and prefer Wollastonite. Again this problem becomes
worse with higher contents. Smaller amounts of Ny Sy and Whiting are not as
serious of a problem.
Here is a quote from Tony,
"Few companies use whiting anymore because it gases so much during
decomposition.
We use wollastonite instead, it is calcium silicate. A high-calcia frit is
even better."
The reason I made my post was to encourage potters to consider rethinking
their glazes and not just accept the status quo and not try to improve on
their glazes. We are always trying to make our ware better because we want
it to be the best possible functional ceramic made for the long term that
it can be. Also, I really think that it is important to make safe glazes for
many reasons. For us this has been a real challenge since we have had pretty
good success with our old G.B./Ny.Sy glaze base, but we are testing right
now and I must admit the G1214W base is much harder and so far I have not
seen the quicker problems that we had with our old base.
Too many hobby potters just mix up a batch of glaze and use it without
really testing it. We plan to send our new tests to one of the places
mentioned in this list before we use them for public consumption.
Seems like Tony and Ron really know their glazes and chemistry.
Chuck
Diane G. Echlin on fri 22 sep 00
Thanks for the info, Chuck! I'm a total novice when it comes to glaze
manipulation, and it's really helpful to have such a clear explanation. I go to
the Digital Fire website on occasion and read, but sometimes I just don't "get"
it. Gotta be a right brain/left brain thing!
Diane in CT
cHuCk wrote:
> > cHuCk wrote:
> >
> > ...and watch out for high contents of Neph. Sy.
> >
> > Why Chuck?
> >
> > Diane, curious in CT
>
> Mostly because I had read a post by Ron Roy that suggested that it was an
> inconsistent material. I don't want to misquote him....but I remember he
> thought more than 20 percent could start to cause some problems. (Please
> correct me if I am out of line) I have been reading a lot on the Digital
> Fire pages too. Just seems like it does not get used as much as it once did.
>
> Whiting is another material that is best left for ground sweetener as it has
> a lot of out gassing. It's better to get your CaCo in a material like
> Wollastonite. This info came from Tony Hansen. I use Mason stains to color a
> lot of our glazes and they recommend that there is CaCo in the glaze. I use
> Whiting to supply it and he suggested that many of the big glaze companies
> do not use it anymore and prefer Wollastonite. Again this problem becomes
> worse with higher contents. Smaller amounts of Ny Sy and Whiting are not as
> serious of a problem.
>
> Here is a quote from Tony,
>
> "Few companies use whiting anymore because it gases so much during
> decomposition.
> We use wollastonite instead, it is calcium silicate. A high-calcia frit is
> even better."
>
> The reason I made my post was to encourage potters to consider rethinking
> their glazes and not just accept the status quo and not try to improve on
> their glazes. We are always trying to make our ware better because we want
> it to be the best possible functional ceramic made for the long term that
> it can be. Also, I really think that it is important to make safe glazes for
> many reasons. For us this has been a real challenge since we have had pretty
> good success with our old G.B./Ny.Sy glaze base, but we are testing right
> now and I must admit the G1214W base is much harder and so far I have not
> seen the quicker problems that we had with our old base.
>
> Too many hobby potters just mix up a batch of glaze and use it without
> really testing it. We plan to send our new tests to one of the places
> mentioned in this list before we use them for public consumption.
>
> Seems like Tony and Ron really know their glazes and chemistry.
>
> Chuck
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Ron Roy on sat 23 sep 00
Hi Chuck and Diane,
I do not think Neph Sy is an inconsistent material but there are reasons to
limits it's use - particularly in glazes that are short of suspending
material.
There are two problems and they work against each other.
Neph Sy is high in sodium (compared to the other feldspars we use) and some
of that soda will dissolve in water and deflocc a glaze if there is not
enough suspending material present - like clay, bentonite etc. Most of the
glazes that settle to hard pan have Neph Sy to blame but it's not the only
material that will lead to this problem. Frit 3110 and Lithium Carb will do
the same. I have even had it happen with Strontium Carb. In the case of
Strontium it may be the way it is processed - it's granulated and it may
just be the medium used to cut dust down.
The other part about Neph Sy that works against suspension is the high
amount of alumina present (again - compared to the spars we use.) This
means we can't get as much raw clay in the glaze - which is usually the
suspending agent in our glazes.
When I am working on cone 6 glazes I try to solve problems in the bucket
and reducing or eliminating Neph Sy is a priority.
** Those of you with a fear of chemistry might want to skip this next paragraph.
I just made up a theoretical glaze with 50% NS then replaced half of that
with G200 - it's a little tricky because you need to understand - K2O is a
better melter than sodium so you can get away with Less KNaO - and wound up
with 2% more EPK in the glaze and reduced the expansion a bit because K2O
has a lower expansion than Na2O. If that would not have solved the
suspension problem I would have replaced half the EPK with ball clay - made
adjustments to balance the alumina and silica and retotaled. If that did
not work I would have added 1 or 2 % bentonite.
It is also true that Neph Sy is a good melter - the only "spar" that is
well melted at cone 6. It is also true that it is perhaps one of the safest
materials we use because the is very little free silica in NS.
All that said - glaze suspension is important and it should also be stable.
Neph Sy will release it's sodium gradually - that makes keeping application
steady from load to load difficult - and that should be avoided as much as
possible.
RR
>> Mostly because I had read a post by Ron Roy that suggested that it was an
>> inconsistent material. I don't want to misquote him....but I remember he
>> thought more than 20 percent could start to cause some problems. (Please
>> correct me if I am out of line) I have been reading a lot on the Digital
>> Fire pages too. Just seems like it does not get used as much as it once did.
>>
>> Whiting is another material that is best left for ground sweetener as it has
>> a lot of out gassing. It's better to get your CaCo in a material like
>> Wollastonite. This info came from Tony Hansen. I use Mason stains to color a
>> lot of our glazes and they recommend that there is CaCo in the glaze. I use
>> Whiting to supply it and he suggested that many of the big glaze companies
>> do not use it anymore and prefer Wollastonite. Again this problem becomes
>> worse with higher contents. Smaller amounts of Ny Sy and Whiting are not as
>> serious of a problem.
>>
>> Here is a quote from Tony,
>>
>> "Few companies use whiting anymore because it gases so much during
>> decomposition.
>> We use wollastonite instead, it is calcium silicate. A high-calcia frit is
>> even better."
>>
>> The reason I made my post was to encourage potters to consider rethinking
>> their glazes and not just accept the status quo and not try to improve on
>> their glazes. We are always trying to make our ware better because we want
>> it to be the best possible functional ceramic made for the long term that
>> it can be. Also, I really think that it is important to make safe glazes for
>> many reasons. For us this has been a real challenge since we have had pretty
>> good success with our old G.B./Ny.Sy glaze base, but we are testing right
>> now and I must admit the G1214W base is much harder and so far I have not
>> seen the quicker problems that we had with our old base.
>>
>> Too many hobby potters just mix up a batch of glaze and use it without
>> really testing it. We plan to send our new tests to one of the places
>> mentioned in this list before we use them for public consumption.
>>
>> Seems like Tony and Ron really know their glazes and chemistry.
>>
>> Chuck
>>
>>
>>__________________________________________________________________________
>>____
>> Send postings to clayart@lsv.ceramics.org
>>
>> You may look at the archives for the list or change your subscription
>> settings from http://www.ceramics.org/clayart/
>>
>> Moderator of the list is Mel Jacobson who may be reached at
>>melpots@pclink.com.
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Diane G. Echlin on sat 23 sep 00
> ** Those of you with a fear of chemistry might want to skip this next paragraph.
Thanks for the warning, I'll cover my eyes while I read!
> I just made up a theoretical glaze with 50% NS then replaced half of that
> with G200 - it's a little tricky because you need to understand - K2O is a
> better melter than sodium so you can get away with Less KNaO - and wound up
> with 2% more EPK in the glaze and reduced the expansion a bit because K2O
> has a lower expansion than Na2O. If that would not have solved the
> suspension problem I would have replaced half the EPK with ball clay - made
> adjustments to balance the alumina and silica and retotaled. If that did
> not work I would have added 1 or 2 % bentonite.
Okay, gonna go look up K2O....drawing a blank....thanks, Ron. Some day I'll learn
this alchemy, if I have to cram in into my head with a shoe horn!
You all are the greatest, as usual!
Diane in CT
Ron Roy on sun 24 sep 00
Hi Diane,
Thats what I had to do - the important part is wanting to have it in there
- how you get it in depends on how thick your scull is I guess. If you need
to know you will find a way.
RR
>this alchemy, if I have to cram in into my head with a shoe horn!
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
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