Jennifer Firestone on sat 5 oct 02
I've tested Ron & John's clear liner glaze (pg 97)
twice now & come up with a lovely soft white
glossy opaque glaze. I've substituted Custer for the G200. Is that the
problem? I thought these two spars were pretty interchangeable. I fire
slowly, up & down, with a pyrometer, ^6 tip touching. All other glazes have
come out beautifully......Thanks for a great book!Jennifer
www.FireKitten.com
John Hesselberth on sat 5 oct 02
Hi Jennifer,
Well, that's interesting. I haven't a clue why that glaze is going
opaque on you. I doubt that it is the Custer. I guess it could be that
you are putting the glaze on quite thick. "Clear" glazes are usually
not perfectly clear and the thicker you put them on the more likely they
are to be partially opaque. Try a thinner coat and see if that helps. I
guess it could also be that you are cooling even more slowly than I do
and your are getting some recrystallization I hadn't realized was
available in that glaze. If a thinner coat doesn't work try cooling
faster.
Regards,
John
On Saturday, October 5, 2002, at 10:57 AM, Jennifer Firestone wrote:
> I've tested Ron & John's clear liner glaze (pg 97)
> twice now & come up with a lovely soft white
> glossy opaque glaze. I've substituted Custer for the G200. Is that the
> problem? I thought these two spars were pretty interchangeable. I fire
> slowly, up & down, with a pyrometer, ^6 tip touching. All other glazes
> have
> come out beautifully......Thanks for a great book!Jennifer
>
> www.FireKitten.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.
>
>
Frog Pond Pottery
PO Box 88
Pocopson, PA 19366
Fax or phone: 610-388-1254
Linda Knapp on mon 4 nov 02
Hopefully you will get better information on this (and share it - I am
really curious!) however I can tell you that I have had different
results with G200 and Custer in one particular glaze (a teadust). They
are indeed supposed to be interchangeable and if you look at the
analysis they are very very very close. However I reran my tests
multiple times and in each test the custer came out very speckled while
the G200 recipe came out with just the right dusting. If I were you I
would try the test again with G200 and see if that changes things.
Now that I have said this I will also say that whenever I test a recipe
that calls for G200 I use custer and if it works as I want I leave it.
G200 is more expensive.
Linda
From cold & dry (for the moment) Seattle.....
Jennifer Firestone wrote:
>I've tested Ron & John's clear liner glaze (pg 97)
>twice now & come up with a lovely soft white
>glossy opaque glaze. I've substituted Custer for the G200. Is that the
>problem? I thought these two spars were pretty interchangeable. I fire
>slowly, up & down, with a pyrometer, ^6 tip touching. All other glazes have
>come out beautifully......Thanks for a great book!Jennifer
>
>www.FireKitten.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 on thu 7 nov 02
Hi Linda and Jennifer,
I would have speculated that it would matter if there was a lot of spare in
a glaze and it was somewhat unbalanced - maybe some difference - but not
change a clear to soft white - lovely or not.
But in this glaze the G200 is only at 20% - when I sub Custer in I get a
little less Al2O3 and more SiO2 - that would make it melt more - not less.
I suspect the Custer Spar is a bad batch - I seem to remember Custer going
through some variation a while back - perhaps that would explain the
results.
With the tea dust glaze - I would expect the crystals would grow better
with Custer - so that does not make sense.
It is not unusual for some materials to vary once in a while. Some times it
takes years for them to clear out of the suppliers stocks.
I have to add - I trust G200 because it comes with an analysis for every
shipment - it is remarkable how consistent it is. I had a conversation with
a rep from a frit manufacturer once - asked him what spar they used - he
said G200 - I said why because you have to pay more shipping? He said yes
it costs us more but it's more reliable.
I'm not trying to say everyone should use G200 - but I am saying that
saving a few dollars on a bag of material is not cost effective for potters
- or frit manufactures - or clay makers.
I am also saying - reliability is more important - or make sure you pretest
everything - or - if you prefer surprises - make sure you introduce the
variable - so you can reproduce it if you like it.
RR
>Hopefully you will get better information on this (and share it - I am
>really curious!) however I can tell you that I have had different
>results with G200 and Custer in one particular glaze (a teadust). They
>are indeed supposed to be interchangeable and if you look at the
>analysis they are very very very close. However I reran my tests
>multiple times and in each test the custer came out very speckled while
>the G200 recipe came out with just the right dusting. If I were you I
>would try the test again with G200 and see if that changes things.
>
>Now that I have said this I will also say that whenever I test a recipe
>that calls for G200 I use custer and if it works as I want I leave it.
>G200 is more expensive.
>
>Linda
> From cold & dry (for the moment) Seattle.....
>
>Jennifer Firestone wrote:
>
>>I've tested Ron & John's clear liner glaze (pg 97)
>>twice now & come up with a lovely soft white
>>glossy opaque glaze. I've substituted Custer for the G200. Is that the
>>problem? I thought these two spars were pretty interchangeable. I fire
>>slowly, up & down, with a pyrometer, ^6 tip touching. All other glazes have
>>come out beautifully......Thanks for a great book!Jennifer
>>
>>www.FireKitten.com
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Linda Knapp on thu 7 nov 02
Ron - Thanks for your comments - what you wrote makes a great deal of
sense with what I saw in my tests.
My point is simply don't assume that subing custer for the G200 in a
glaze will not effect the glaze - it sometimes does. When in doubt test.
RE: The Teadust Glaze - I get more green speckles with custer than G200
so that sounds consistent with what you are saying. But why do you say
it? Is it the variation of Al2O3 to SiO2 or the variation of MgO2? Our
solution was to switch to G200 for the Teadust glaze but I would like to
understand it better - one of these days I am going to do a line blend
between G200 and Custer with it I think.
Linda
from (right now) rainy Seattle
Ron Roy wrote:
>Hi Linda and Jennifer,
>
>I would have speculated that it would matter if there was a lot of spare in
>a glaze and it was somewhat unbalanced - maybe some difference - but not
>change a clear to soft white - lovely or not.
>
>But in this glaze the G200 is only at 20% - when I sub Custer in I get a
>little less Al2O3 and more SiO2 - that would make it melt more - not less.
>
>I suspect the Custer Spar is a bad batch - I seem to remember Custer going
>through some variation a while back - perhaps that would explain the
>results.
>
>With the tea dust glaze - I would expect the crystals would grow better
>with Custer - so that does not make sense.
>
>It is not unusual for some materials to vary once in a while. Some times it
>takes years for them to clear out of the suppliers stocks.
>
>I have to add - I trust G200 because it comes with an analysis for every
>shipment - it is remarkable how consistent it is. I had a conversation with
>a rep from a frit manufacturer once - asked him what spar they used - he
>said G200 - I said why because you have to pay more shipping? He said yes
>it costs us more but it's more reliable.
>
>I'm not trying to say everyone should use G200 - but I am saying that
>saving a few dollars on a bag of material is not cost effective for potters
>- or frit manufactures - or clay makers.
>
>I am also saying - reliability is more important - or make sure you pretest
>everything - or - if you prefer surprises - make sure you introduce the
>variable - so you can reproduce it if you like it.
>
>RR
>
>
>
>>Hopefully you will get better information on this (and share it - I am
>>really curious!) however I can tell you that I have had different
>>results with G200 and Custer in one particular glaze (a teadust). They
>>are indeed supposed to be interchangeable and if you look at the
>>analysis they are very very very close. However I reran my tests
>>multiple times and in each test the custer came out very speckled while
>>the G200 recipe came out with just the right dusting. If I were you I
>>would try the test again with G200 and see if that changes things.
>>
>>Now that I have said this I will also say that whenever I test a recipe
>>that calls for G200 I use custer and if it works as I want I leave it.
>>G200 is more expensive.
>>
>>Linda
>>From cold & dry (for the moment) Seattle.....
>>
>>Jennifer Firestone wrote:
>>
>>
>>
>>>I've tested Ron & John's clear liner glaze (pg 97)
>>>twice now & come up with a lovely soft white
>>>glossy opaque glaze. I've substituted Custer for the G200. Is that the
>>>problem? I thought these two spars were pretty interchangeable. I fire
>>>slowly, up & down, with a pyrometer, ^6 tip touching. All other glazes have
>>>come out beautifully......Thanks for a great book!Jennifer
>>>
>>>www.FireKitten.com
>>>
>>>
>
>Ron Roy
>RR#4
>15084 Little Lake Road
>Brighton, Ontario
>Canada
>K0K 1H0
>Phone: 613-475-9544
>Fax: 613-475-3513
>
>______________________________________________________________________________
>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 sun 10 nov 02
Hi Linda,
Crystal growth is favoured by silica - because when crystals form they need
extra silica - there is a section in Taylor and Bulls - "Ceramic Glazes"
which explains how crystals rob the surrounding glaze of silica - sometimes
to the extent that the surrounding glaze is less durable because of the
reduced SiO2.
Alumina inhibits crystal growth (except in the case of alumina mattes -
Al2O3 oversupplied) - Custer has more silica and less alumina than G200.
Slower cooling at the "right time" will give bigger and more crystals by
the way.
RR
>Ron - Thanks for your comments - what you wrote makes a great deal of
>sense with what I saw in my tests.
>My point is simply don't assume that subing custer for the G200 in a
>glaze will not effect the glaze - it sometimes does. When in doubt test.
>
>RE: The Teadust Glaze - I get more green speckles with custer than G200
>so that sounds consistent with what you are saying. But why do you say
>it? Is it the variation of Al2O3 to SiO2 or the variation of MgO2? Our
>solution was to switch to G200 for the Teadust glaze but I would like to
>understand it better - one of these days I am going to do a line blend
>between G200 and Custer with it I think.
>
>Linda
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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