Steve Slatin on mon 6 sep 04
flint and silica.
Ron --
Extremely useful information, and it begs a question
... Quartz can be put into a recipe as 100% SiO2;
Flint as 97% SiO2 and 3% CaO and commercial "Silica"
as 99.8% SiO2, with the balance inconsequential
amounts of Alumina and Iron.
But the structure of the Silica is not the same in all
sources. Subbing (say) silica for flint is easy
enough on a molar basis; you increase the CaO
elsewhere in the recipe and use a correspondingly
lesser weight of silica than flint -- but will the
different structure of the material have an effect on
melt/glaze formation?
It's tempting to presume that there will be no
difference, as by final melt temperature the silica
"should" be completely integrated into the final
glaze, but does experimentation show that the
substitution gives identical results? It occurs to me
that the amorphous form, having a different melting
point might integrate into a glaze at a different
temperature than a crystalline form, thus
having consequences for glaze turbidity, 'movement' of
colorants, smoothness of surface, etc.
Regards -- Steve Slatin (who only has one source of
Silica in his studio, and who consequently ALWAYS subs
in recipes)
--- Ron Roy wrote:
> Flint is not all quartz - there is some CaO in it.
>
> Quartz - almost pure SiO2
>
> Quartz is a crystalline form of SiO2- so is
> Cristobalite and so is
> Tridimite - amorphous silica is a non-crystalline
> form of SiO2.
>
> Hamer has ten pages on SiO2 - it is an important
> oxide for us potters - the
> more we know about it the easier it will be to solve
> problems attributed to
> it's different forms.
>
=====
Steve Slatin -- Entry-level potter, journeyman loafer, master obfuscator
Sequim, Washington, USA
48.0937°N, 123.1465°W or thereabouts
__________________________________
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David Hewitt on tue 7 sep 04
flint and silica.
In thinking of glaze substitutions, does anyone try to take into account
the amount of moisture (water) added to quartz ( and for that matter to
Cornish Stone)
The quartz that I buy has a percentage of water added to reduce the
hazard of breathing in particles of silica. I am not sure what
percentage this is, but think that it is a least 5%. Perhaps Steve mills
can tell me what it is that I get from Bath Potters'
I would be interested in any views on this.
David
In message , Steve Slatin writes
>Ron --
>
>Extremely useful information, and it begs a question
>... Quartz can be put into a recipe as 100% SiO2;
>Flint as 97% SiO2 and 3% CaO and commercial "Silica"
>as 99.8% SiO2, with the balance inconsequential
>amounts of Alumina and Iron.
>
>But the structure of the Silica is not the same in all
>sources. Subbing (say) silica for flint is easy
>enough on a molar basis; you increase the CaO
>elsewhere in the recipe and use a correspondingly
>lesser weight of silica than flint -- but will the
>different structure of the material have an effect on
>melt/glaze formation?
>
>It's tempting to presume that there will be no
>difference, as by final melt temperature the silica
>"should" be completely integrated into the final
>glaze, but does experimentation show that the
>substitution gives identical results? It occurs to me
>that the amorphous form, having a different melting
>point might integrate into a glaze at a different
>temperature than a crystalline form, thus
>having consequences for glaze turbidity, 'movement' of
>colorants, smoothness of surface, etc.
>
>Regards -- Steve Slatin (who only has one source of
>Silica in his studio, and who consequently ALWAYS subs
>in recipes)
>
>
>--- Ron Roy wrote:
>
>> Flint is not all quartz - there is some CaO in it.
>>
>> Quartz - almost pure SiO2
>>
>> Quartz is a crystalline form of SiO2- so is
>> Cristobalite and so is
>> Tridimite - amorphous silica is a non-crystalline
>> form of SiO2.
>>
>> Hamer has ten pages on SiO2 - it is an important
>> oxide for us potters - the
>> more we know about it the easier it will be to solve
>> problems attributed to
>> it's different forms.
>>
>
>
>Steve Slatin -- Entry-level potter, journeyman loafer, master obfuscator
> Sequim, Washington, USA
> 48.0937°N, 123.1465°W or thereabouts
>
>
>
>__________________________________
>Do you Yahoo!?
>Yahoo! Mail Address AutoComplete - You start. We finish.
>http://promotions.yahoo.com/new_mail
--
David Hewitt
Web:- http://www.dhpot.demon.co.uk
Dorothy Feibleman on tue 7 sep 04
flint and silica.
Dear David,
I have been using a wonderful machine at Ia company in Japan that measures
the amount of water and some of it is up to almost 20 percent, it is
different in each bag. For the work I have been doing, it is necessary to
get it exact in the clay bodies. Maybe you should dry it out when you do a
firing on a kiln shelf or container near the kiln. I would love to buy the
machine if it is available in the UK, otherwise, I will save up and get one
in Japan some year. The same place has electric morter and pestals and that
is great too! I never saw those here.
Maybe the far eastern producers of materials leave more water in, but 19.8%
is pretty high and the low for the same product was about 16.2%.
Best,
dorothy
>In thinking of glaze substitutions, does anyone try to take into account
>the amount of moisture (water) added to quartz ( and for that matter to
>Cornish Stone)
>
>The quartz that I buy has a percentage of water added to reduce the
>hazard of breathing in particles of silica. I am not sure what
>percentage this is, but think that it is a least 5%. Perhaps Steve mills
>can tell me what it is that I get from Bath Potters'
>
>I would be interested in any views on this.
>
>David
>In message , Steve Slatin writes
>>Ron --
>>
>>Extremely useful information, and it begs a question
>>... Quartz can be put into a recipe as 100% SiO2;
>>Flint as 97% SiO2 and 3% CaO and commercial "Silica"
>>as 99.8% SiO2, with the balance inconsequential
>>amounts of Alumina and Iron.
>>
>>But the structure of the Silica is not the same in all
>>sources. Subbing (say) silica for flint is easy
>>enough on a molar basis; you increase the CaO
>>elsewhere in the recipe and use a correspondingly
>>lesser weight of silica than flint -- but will the
>>different structure of the material have an effect on
>>melt/glaze formation?
>>
>>It's tempting to presume that there will be no
>>difference, as by final melt temperature the silica
>>"should" be completely integrated into the final
>>glaze, but does experimentation show that the
>>substitution gives identical results? It occurs to me
>>that the amorphous form, having a different melting
>>point might integrate into a glaze at a different
>>temperature than a crystalline form, thus
>>having consequences for glaze turbidity, 'movement' of
>>colorants, smoothness of surface, etc.
>>
>>Regards -- Steve Slatin (who only has one source of
>>Silica in his studio, and who consequently ALWAYS subs
>>in recipes)
>>
>>
>>--- Ron Roy wrote:
>>
>>> Flint is not all quartz - there is some CaO in it.
>>>
>>> Quartz - almost pure SiO2
>>>
>>> Quartz is a crystalline form of SiO2- so is
>>> Cristobalite and so is
>>> Tridimite - amorphous silica is a non-crystalline
>>> form of SiO2.
>>>
>>> Hamer has ten pages on SiO2 - it is an important
>>> oxide for us potters - the
>>> more we know about it the easier it will be to solve
>>> problems attributed to
>>> it's different forms.
>>>
>>
>>
>>Steve Slatin -- Entry-level potter, journeyman loafer, master obfuscator
>> Sequim, Washington, USA
>> 48.0937=B0N, 123.1465=B0W or thereabouts
>>
>>
>>
>>__________________________________
>>Do you Yahoo!?
>>Yahoo! Mail Address AutoComplete - You start. We finish.
>>http://promotions.yahoo.com/new_mail
>
>--
>David Hewitt
>
>Web:- http://www.dhpot.demon.co.uk
>
>___________________________________________________________________________=
___
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Steve Mills on wed 8 sep 04
flint and silica.
Dear David et al,
As Quartz, Flint, and Cornish Stone are all water ground they are filter
press dried. The first two to around 12 percent moisture, the last to 14
percent. These percentages are close but not exact, and relate to our
raw materials Supplier, other processing companies may do it
differently!
In my production past I kept all my basic powdered materials in heavy-
duty cardboard drums which effectively dried them out. So long as I wore
a respirator when weighing up I was O.K.
I didn't always remember, however I'm still around.
Well at least I Think I am.
Maybe I'm a figment of my own imagination!
Steve
Bath
UK
Maybe!
In message , David Hewitt writes
>In thinking of glaze substitutions, does anyone try to take into account
>the amount of moisture (water) added to quartz ( and for that matter to
>Cornish Stone)
>
>The quartz that I buy has a percentage of water added to reduce the
>hazard of breathing in particles of silica. I am not sure what
>percentage this is, but think that it is a least 5%. Perhaps Steve mills
>can tell me what it is that I get from Bath Potters'
>
>I would be interested in any views on this.
>
>David
--
Steve Mills
Bath
UK
Ron Roy on wed 8 sep 04
flint and silica.
Hi Steve,
I would think you would not notice any difference in most glazes - perhaps
a bit of a difference in some unbalanced glazes - some Shino's don't like
CaO for for instance. So In that respect you are right.
Yes again - if you sub the different forms on a mol for mol basis then
there would be no decernable difference - in a glaze. But if you ask the
same question for a clay body we may have a more significant difference -
CaO does not help surpress cristobalite formation and in fact will
encourage it for instance
Yes again - amorphous silica is more easily integrated into the melt.
Particle size as well - has an effect on how fast melting proceedes. Try
making a glaze with silica sand and see how far you get for instance.
Durability and fit are profoundly affected by SiO2 - as it surface quality
- it is one of the reasons that I find the Hamer book so attractive - 10
pages on the most important oxide we use - what could be more appropriate.
I find silica to be a facinating subject - 60 to 70% of our glazes and
clays are made up of silica - the more we know about it the better off we
are.
Thanks for your comments - more than I would expect from an "entry-level
potter" by the way. Perhaps you were involved in another life?
RR
>Extremely useful information, and it begs a question
>... Quartz can be put into a recipe as 100% SiO2;
>Flint as 97% SiO2 and 3% CaO and commercial "Silica"
>as 99.8% SiO2, with the balance inconsequential
>amounts of Alumina and Iron.
>
>But the structure of the Silica is not the same in all
>sources. Subbing (say) silica for flint is easy
>enough on a molar basis; you increase the CaO
>elsewhere in the recipe and use a correspondingly
>lesser weight of silica than flint -- but will the
>different structure of the material have an effect on
>melt/glaze formation?
>
>It's tempting to presume that there will be no
>difference, as by final melt temperature the silica
>"should" be completely integrated into the final
>glaze, but does experimentation show that the
>substitution gives identical results? It occurs to me
>that the amorphous form, having a different melting
>point might integrate into a glaze at a different
>temperature than a crystalline form, thus
>having consequences for glaze turbidity, 'movement' of
>colorants, smoothness of surface, etc.
>
>Regards -- Steve Slatin (who only has one source of
>Silica in his studio, and who consequently ALWAYS subs
>in recipes)
>
>
>--- Ron Roy wrote:
>
>> Flint is not all quartz - there is some CaO in it.
>>
>> Quartz - almost pure SiO2
>>
>> Quartz is a crystalline form of SiO2- so is
>> Cristobalite and so is
>> Tridimite - amorphous silica is a non-crystalline
>> form of SiO2.
>>
>> Hamer has ten pages on SiO2 - it is an important
>> oxide for us potters - the
>> more we know about it the easier it will be to solve
>> problems attributed to
>> it's different forms.
>>
>
>=====
>Steve Slatin
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on thu 9 sep 04
flint and silica.
Hi david,
I can remember - getting my first bag of Cornish Stone - it was wet - and lumpy.
I made sure it was dried out before I used it in a glaze. I cannot think of
how to make sure of getting the same amount each time.
I should say I could I suppose but letting the whole bag dry is a simpler
solution - and make sure the dust is not breathed.
RR
>In thinking of glaze substitutions, does anyone try to take into account
>the amount of moisture (water) added to quartz ( and for that matter to
>Cornish Stone)
>
>The quartz that I buy has a percentage of water added to reduce the
>hazard of breathing in particles of silica. I am not sure what
>percentage this is, but think that it is a least 5%. Perhaps Steve mills
>can tell me what it is that I get from Bath Potters'
>
>I would be interested in any views on this.
>
>David
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
william schran on thu 9 sep 04
flint and silica.
Ron wrote:>I can remember - getting my first bag of Cornish Stone -
it was wet - and lumpy.<
I have a unopened bag that I can feel is lumpy and I have a plastic
jar with Cornwall Stone that looks like a greenhouse, water beaded up
on the inside.
Can this material be dried out in a ^06 bisque, or is that too high a
temperature?
How about just red heat (1200=B0F)?
Bill
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