doug shea on sat 20 nov 99
One and all,
I'm hoping someone out there can help me. At the community
studio where I work, there is a glaze (^10R) that we call Satin Matte
Blue Green. The bucket is at least 8 years old and getting rather low.
I started to mix some up tonight, but became confused (not an unusual
occurrence) when I looked at the recipe.
When thin, the glaze is dark matte brown, shades through mossy
green matte, to a matte dark blue, and finally to a cratered glossy
royal blue when very thick.
This glaze is practically garaunteed NOT to be food-safe.
Here's the recipe as it appears on the recipe card:
Satin Matte Blue/Green (aka Nazareth Oatmeal Green)
^9-10R
Custer Spar 36
Spodumene 16 (was 14, but changed to 16)
Whiting 25
Gerst. Borate 5
EPK 20
Red Iron Ox 4
"Beautiful Blue/ Green Matte"
My questions are: Could this recipe be the same as the glaze we
have in the bucket? If so, where does the blue come from? Would using
Spanish Red Iron Oxide instead of Dominican Iron Oxide make a big
difference? I mixed up a test batch tonight and the color of the raw
glaze test was medium red, while the original glaze is a greyish beige.
We have Spanish Red Iron Oxide now, and I think we used Dominican Iron
Oxide long ago. I should mention that the glaze works as well now as it
did then. My first piece is glazed in this glaze and it looks as good
as my latest piece (as far as the glaze quality is concerned).
Any help would be greatly appreciated. I've grown to like this
glaze alot.
Jim Shea
Tom Buck on mon 22 nov 99
Mr. Shea:
Try to find "Pioneer Pottery" by Michael Cardew and read
Pp140-143, espy the footnotes.
Your C10R glaze contains common materials and uses iron oxide red
as the colourant. It would be food-safe because iron oxide doesn't leach
easily and even if it did, we need a fair amount of Fe+++ ion every day in
our diet so micrograms of iron ion would not be of concern to most people.
The blue comes from a crystalline state of FeO that reduction
generates from Fe2O3 and yes the purity of the red iron oxide would have a
bearing on the actual colour you obtain. BTW, a very similar mix is well
established; it is called Penland Purple and yields tans where thin and
dark blue where thick.
Ask your supplier for an analysis of your current RIO ... how much
Iron (or Iron Oxide Fe2O3) is present in the powder. I'd like to know too.
Good pots. Til later. Peace. Tom B.
Tom Buck ) tel: 905-389-2339 (westend Lake Ontario,
province of Ontario, Canada). mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada
Ron Roy on thu 25 nov 99
Hi Jim,
You are right about this not being a durable glaze - it is very low in SiO2
for a cone 10 glaze - as most clay mattes are.
I have calculated it out using both the old Foote Spod and the newer Sussi
spod and it is very similar either way.
It may be the original was mixed up with black iron oxide - if red had been
used the raw glaze would have looked iron red with that much red iron.
I can't find any info on that would explain the blue - several tests
describe iron blues as an optical effect - related to the size of bubbles
in a glaze which reflect the blue spectrum. Perhaps this has something to
do with what you are seeing.
RR
>----------------------------Original message----------------------------
>One and all,
> I'm hoping someone out there can help me. At the community
>studio where I work, there is a glaze (^10R) that we call Satin Matte
>Blue Green. The bucket is at least 8 years old and getting rather low.
> I started to mix some up tonight, but became confused (not an unusual
>occurrence) when I looked at the recipe.
>
> When thin, the glaze is dark matte brown, shades through mossy
>green matte, to a matte dark blue, and finally to a cratered glossy
>royal blue when very thick.
>
>This glaze is practically garaunteed NOT to be food-safe.
>
> Here's the recipe as it appears on the recipe card:
>
> Satin Matte Blue/Green (aka Nazareth Oatmeal Green)
> ^9-10R
>
> Custer Spar 36
> Spodumene 16 (was 14, but changed to 16)
> Whiting 25
> Gerst. Borate 5
> EPK 20
> Red Iron Ox 4
> "Beautiful Blue/ Green Matte"
>
>
> My questions are: Could this recipe be the same as the glaze we
>have in the bucket? If so, where does the blue come from? Would using
>Spanish Red Iron Oxide instead of Dominican Iron Oxide make a big
>difference? I mixed up a test batch tonight and the color of the raw
>glaze test was medium red, while the original glaze is a greyish beige.
> We have Spanish Red Iron Oxide now, and I think we used Dominican Iron
>Oxide long ago. I should mention that the glaze works as well now as it
>did then. My first piece is glazed in this glaze and it looks as good
>as my latest piece (as far as the glaze quality is concerned).
>
> Any help would be greatly appreciated. I've grown to like this
>glaze alot.
>
> Jim Shea
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Hank Murrow on sat 27 nov 99
Good Morning Ron and Jim; I may be able to suggest something to extend
Ron's idea of the iron blue. The glaze has boron from the Gerstley and may
have phosphorus from the spodumene if it's the Low Melt amblygonite version
anyway. In any case, boron and phosphorus are glass-formers(network
modifiers) and each will form a miscible glaze fluid within the silicate
melt. These glazes are sort of like mayonnaise in that one semi-liquid is
suspended within another as small droplets. So they refract the light to
produce the blue color. Wood ash if taken from fruitwood contains enough
P2O5 to do the trick, as the Chinese potters discovered when they made
their beautiful Chuns. I agree that the glaze is pretty low in silica, and
chuns run to very high silica levels. Anyway, I'm thinking about it and
will get a test in the kiln soon. Regards, Hank in Eugene
>----------------------------Original message----------------------------
>Hi Jim,
>
>You are right about this not being a durable glaze - it is very low in SiO2
>for a cone 10 glaze - as most clay mattes are.
>
>I have calculated it out using both the old Foote Spod and the newer Sussi
>spod and it is very similar either way.
>
>It may be the original was mixed up with black iron oxide - if red had been
>used the raw glaze would have looked iron red with that much red iron.
>
>I can't find any info on that would explain the blue - several tests
>describe iron blues as an optical effect - related to the size of bubbles
>in a glaze which reflect the blue spectrum. Perhaps this has something to
>do with what you are seeing.
>
>RR
>
>>----------------------------Original message----------------------------
>>One and all,
>> I'm hoping someone out there can help me. At the community
>>studio where I work, there is a glaze (^10R) that we call Satin Matte
>>Blue Green. The bucket is at least 8 years old and getting rather low.
>> I started to mix some up tonight, but became confused (not an unusual
>>occurrence) when I looked at the recipe.
>>
>> When thin, the glaze is dark matte brown, shades through mossy
>>green matte, to a matte dark blue, and finally to a cratered glossy
>>royal blue when very thick.
>>
>>This glaze is practically garaunteed NOT to be food-safe.
>>
>> Here's the recipe as it appears on the recipe card:
>>
>> Satin Matte Blue/Green (aka Nazareth Oatmeal Green)
>> ^9-10R
>>
>> Custer Spar 36
>> Spodumene 16 (was 14, but changed to 16)
>> Whiting 25
>> Gerst. Borate 5
>> EPK 20
>> Red Iron Ox 4
>> "Beautiful Blue/ Green Matte"
>>
>>
>> My questions are: Could this recipe be the same as the glaze we
>>have in the bucket? If so, where does the blue come from? Would using
>>Spanish Red Iron Oxide instead of Dominican Iron Oxide make a big
>>difference? I mixed up a test batch tonight and the color of the raw
>>glaze test was medium red, while the original glaze is a greyish beige.
>> We have Spanish Red Iron Oxide now, and I think we used Dominican Iron
>>Oxide long ago. I should mention that the glaze works as well now as it
>>did then. My first piece is glazed in this glaze and it looks as good
>>as my latest piece (as far as the glaze quality is concerned).
>>
>> Any help would be greatly appreciated. I've grown to like this
>>glaze alot.
>>
>> Jim Shea
>
>Ron Roy
>93 Pegasus Trail
>Scarborough
>Ontario, Canada
>M1G 3N8
>Evenings 416-439-2621
>Fax 416-438-7849
| |
|
