Marcia Selsor on fri 18 apr 03
Dear John,
I have been busy mixing glazes and firing lately. I have a question.
We have some of the dark lavender Cobalt and bright pink cobalt carb. as
a result of combining all of our members chemicals. We have used some of
the two tones of rutile. I am happy to report that the Caribbean Cobalt
Green finally went green with a lot more rutile added to it.
My new question is in regards to CROCUS MARTIS. I prdered some from
Seattle Pottery and they sent Spanish Red iron which they said was the
same thing. Clayart Center mentions it is the same thing on their
website. Hamer and Hamer says it is Anhydrous Iron Sulphate (I think
that was the correct description) which means it is a salt, I believe. I
was able to get some after a search from a supplier in Portland, Maine.
I knew Crocus Martis many years ago. I am surprised itn is being passed
off now as an equivalent to Spanish Iron Oxide. Am I missing something
here? Crocus Martis is used in Over glaze decoration on Tin Glaze.
Is it really the same as Spanish Iron Oxide. I am skeptical.
Please advise,
Marcia Selsor
--
Tuscany in 2003
http://home.attbi.com/~m.selsor/Tuscany2003.html
John Hesselberth on fri 18 apr 03
Hi Everyone,
As many of you know, I have been trying to track down what differences
there might be in the copper carbonates, cobalt carbonates, and rutiles
being offered for sale by pottery supply dealers. In other words, are
there any "bad" lots of these things being sold.
The bottom line is that I haven't been able to find any bad stuff among
these three ingredients. I offer considerable detail on my experiments
below and some hypotheses on what may be going on with people who are
reporting trouble.
First, copper carbonate
I have obtained copper carbonate samples from Axner, U.S. Pigments,
DelVal (Judy Wilson at DelVal has been my supplier for about 10 years
and I've never had any question about the quality of the materials she
sells) plus one sample sent to me with the supplier not identified (but
it was from the northeast U.S.). I also still have some of the "old"
grey-green copper carbonate that I bought from DelVal 2 or 3 years ago.
Some comments I picked up from the various suppliers I talked to.
There is considerable consolidation going on in the manufacture of
copper carbonate. If we are not already down to 1 manufacturer we may
be soon. Our direct suppliers started switching to the new, brighter
green material 1-2 years ago because they were either having trouble
with their current supplier or they could no longer get the old
material. I would guess there are still at least 2 manufacturers in
the system judging from the color of the materials I tested (or 2
different grades or mesh sizes)--anyhow the new materials are not all
identical in appearance of the powder.
I put these samples of copper carbonate into Spearmint--one of the
glazes in Mastering Cone 6 Glazes which is a bit color-fussy. For those
who haven't seen it, it is a cool green and some people have reported
getting a more yellowy green than we show in the book--more on that in
a minute. When I compared these various copper carbonates (using the
same rutile and all other ingredients) on the same clay body, I could
see only the tiniest of differences. If anything (and I am really
picking at nits here) the original grey-green copper gave a slightly
yellower green in the fired glaze.
The biggest difference was dependent on the clay body it was on. I used
a grolleg porcelain, a white stoneware and a tan stoneware. This is a
fairly opaque glaze and the white stoneware and the tan stoneware
samples were quite similar--although a little bit of the clay color
influenced the final color of the fired glaze. The porcelain samples
matched the color of the glaze in the book pretty well. This glaze is
significantly different looking on porcelain vs. stoneware and that may
account for some of the problems people are having reproducing the
color in the book. Apparently that extra neph sy that is in a typical
cone 6 porcelain body had quite an effect--at least on this particular
glaze. I still wouldn't call the stoneware samples a "yucky
yellow-green". Rather they were slightly darker and greyer than the
porcelain samples with more body color showing through where the glaze
was thin.
Anyhow I conclude there is nothing wrong with the brighter green copper
carbonate we are now buying. It gave fully equivalent results to the
older material. That is not to say there might not be a bad lot
running around or a supplier who is buying a significantly less pure
grade of the material--there might be, but I saw no evidence of it.
On to cobalt carbonate
I obtained cobalt carbonate from DelVal, Axner, U.S. Pigments, and 2
samples from the northeast U.S. One of those 2 samples was distinctly
a very grey-lavender instead of the normal bright lavender we are used
to. I thought I might have a smoking gun here. Of the ones that were
in the bright lavender family some were less bright (more white) than
others so there are obviously still some multiples sources and/or
grades of cobalt in our system.
I put the cobalt carbonate samples into Semimatte Base 2 (from MC6G, of
course) at a 1% level along with 6% rutile (I just love that stuff--I
put it in everything). I only used white and tan stoneware for these
samples. Again, no discernible difference in fired glaze
color--nothing that couldn't be explained by slight variation in
thickness of application. Even the grey-lavender sample seemed to be
fine.
So again, if there is any "bad" cobalt in the system I have yet to find
it.
Now rutile
I had more samples of rutile because several of our suppliers carry
more than one grade. I had dark and regular rutile from DelVal (the
dark is several years old and Judy can no longer get it from her
supplier), ceramic light from Axner, ceramic-and ceramic-lite grades
from U.S. Pigments, a regular rutile from the unidentified supplier,
and a dark rutile from Portland Pottery Supply--South (used to be Corey
Ceramics--they are in Mass) (Pat says she can still get this from her
supplier if anyone is interested) -- 7 samples in all. I used
Spearmint to test these with DelVal "old" copper carbonate in all
samples. Again I tested only on white and tan stoneware.
These various rutiles were quite different in color of the powder
varying from a light tan to medium brown. But again only the tiniest
differences in fired glaze colors. I may not be using a glaze where
rutile is critical to color--some of you may remember a post by Richard
Aerni a couple years ago where he described what he had learned about
the various grades of rutile and how important it was to him to get the
"right" one for his glaze--but I just could not see any differences
worth talking about. I would add, though, that I did have one or two
samples on porcelain through this process and there were slightly
bigger difference there. The number of samples was too small to be
certain, but I may rerun this test with a full porcelain set sometime
in the future.
Sooooo, what's going on???
I would speculate that some of us are seeing 1 of several things when
we are suspicious of "bad" materials and not getting glaze colors we
expected:
1. There still could be some bad copper, cobalt, or rutile out there
and I just haven't found it.
2. Thickness of application can make a big difference in the appearance
of a fired glaze.
3. These tests brought home again to me how different a glaze can look
on different clay bodies--particularly stoneware vs. porcelain in my
tests.
4. When we buy materials in less than full bag lots, there is a
definite possibility of a "mix" occurring when the materials are
weighed out at the pottery supply dealer's shop. Most of our materials
are white powders and are impossible to tell from each other by
appearance. Always test new purchases of materials in a 100 or 200 gram
batch changing only one material at a time. And, of course, buy full
bags whenever you possibly can and keep or record the information on
lot and mine or manufacturer that is printed on the bag.
5. Different firing temperatures can cause glazes to look significantly
different. Always use cones on every shelf in every firing.
6. Lastly there is always the possibility of potter error in mixing the
glaze. I would be particularly concerned working in a community studio
where you don't know how careful the person is who mixed the last batch.
Well, I hope all this helps. It was an interesting, yet frustrating
excercise. I started from the point of view that I would probably find
a smoking gun or two--but it/they just weren't there.
I am still open to testing an occasional batch if someone really thinks
they have found a bad lot. Let me know.
Regards,
John
http://www.frogpondpottery.com
http://www.masteringglazes.com
Jim Kasper on fri 18 apr 03
John,
What about cobolt oxide and copper oxide? Also why use the carbonates
instead of oxides?
Regards,
Jim
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of John
Hesselberth
Sent: Friday, April 18, 2003 12:17 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Copper, cobalt, and rutile (long)
Hi Everyone,
As many of you know, I have been trying to track down what differences
there might be in the copper carbonates, cobalt carbonates, and rutiles
being offered for sale by pottery supply dealers. In other words, are
there any "bad" lots of these things being sold.
The bottom line is that I haven't been able to find any bad stuff among
these three ingredients. I offer considerable detail on my experiments
below and some hypotheses on what may be going on with people who are
reporting trouble.
First, copper carbonate
I have obtained copper carbonate samples from Axner, U.S. Pigments,
DelVal (Judy Wilson at DelVal has been my supplier for about 10 years
and I've never had any question about the quality of the materials she
sells) plus one sample sent to me with the supplier not identified (but
it was from the northeast U.S.). I also still have some of the "old"
grey-green copper carbonate that I bought from DelVal 2 or 3 years ago.
Some comments I picked up from the various suppliers I talked to.
There is considerable consolidation going on in the manufacture of
copper carbonate. If we are not already down to 1 manufacturer we may
be soon. Our direct suppliers started switching to the new, brighter
green material 1-2 years ago because they were either having trouble
with their current supplier or they could no longer get the old
material. I would guess there are still at least 2 manufacturers in
the system judging from the color of the materials I tested (or 2
different grades or mesh sizes)--anyhow the new materials are not all
identical in appearance of the powder.
I put these samples of copper carbonate into Spearmint--one of the
glazes in Mastering Cone 6 Glazes which is a bit color-fussy. For those
who haven't seen it, it is a cool green and some people have reported
getting a more yellowy green than we show in the book--more on that in
a minute. When I compared these various copper carbonates (using the
same rutile and all other ingredients) on the same clay body, I could
see only the tiniest of differences. If anything (and I am really
picking at nits here) the original grey-green copper gave a slightly
yellower green in the fired glaze.
The biggest difference was dependent on the clay body it was on. I used
a grolleg porcelain, a white stoneware and a tan stoneware. This is a
fairly opaque glaze and the white stoneware and the tan stoneware
samples were quite similar--although a little bit of the clay color
influenced the final color of the fired glaze. The porcelain samples
matched the color of the glaze in the book pretty well. This glaze is
significantly different looking on porcelain vs. stoneware and that may
account for some of the problems people are having reproducing the
color in the book. Apparently that extra neph sy that is in a typical
cone 6 porcelain body had quite an effect--at least on this particular
glaze. I still wouldn't call the stoneware samples a "yucky
yellow-green". Rather they were slightly darker and greyer than the
porcelain samples with more body color showing through where the glaze
was thin.
Anyhow I conclude there is nothing wrong with the brighter green copper
carbonate we are now buying. It gave fully equivalent results to the
older material. That is not to say there might not be a bad lot
running around or a supplier who is buying a significantly less pure
grade of the material--there might be, but I saw no evidence of it.
On to cobalt carbonate
I obtained cobalt carbonate from DelVal, Axner, U.S. Pigments, and 2
samples from the northeast U.S. One of those 2 samples was distinctly
a very grey-lavender instead of the normal bright lavender we are used
to. I thought I might have a smoking gun here. Of the ones that were
in the bright lavender family some were less bright (more white) than
others so there are obviously still some multiples sources and/or
grades of cobalt in our system.
I put the cobalt carbonate samples into Semimatte Base 2 (from MC6G, of
course) at a 1% level along with 6% rutile (I just love that stuff--I
put it in everything). I only used white and tan stoneware for these
samples. Again, no discernible difference in fired glaze
color--nothing that couldn't be explained by slight variation in
thickness of application. Even the grey-lavender sample seemed to be
fine.
So again, if there is any "bad" cobalt in the system I have yet to find
it.
Now rutile
I had more samples of rutile because several of our suppliers carry
more than one grade. I had dark and regular rutile from DelVal (the
dark is several years old and Judy can no longer get it from her
supplier), ceramic light from Axner, ceramic-and ceramic-lite grades
from U.S. Pigments, a regular rutile from the unidentified supplier,
and a dark rutile from Portland Pottery Supply--South (used to be Corey
Ceramics--they are in Mass) (Pat says she can still get this from her
supplier if anyone is interested) -- 7 samples in all. I used
Spearmint to test these with DelVal "old" copper carbonate in all
samples. Again I tested only on white and tan stoneware.
These various rutiles were quite different in color of the powder
varying from a light tan to medium brown. But again only the tiniest
differences in fired glaze colors. I may not be using a glaze where
rutile is critical to color--some of you may remember a post by Richard
Aerni a couple years ago where he described what he had learned about
the various grades of rutile and how important it was to him to get the
"right" one for his glaze--but I just could not see any differences
worth talking about. I would add, though, that I did have one or two
samples on porcelain through this process and there were slightly
bigger difference there. The number of samples was too small to be
certain, but I may rerun this test with a full porcelain set sometime
in the future.
Sooooo, what's going on???
I would speculate that some of us are seeing 1 of several things when
we are suspicious of "bad" materials and not getting glaze colors we
expected:
1. There still could be some bad copper, cobalt, or rutile out there
and I just haven't found it.
2. Thickness of application can make a big difference in the appearance
of a fired glaze.
3. These tests brought home again to me how different a glaze can look
on different clay bodies--particularly stoneware vs. porcelain in my
tests.
4. When we buy materials in less than full bag lots, there is a
definite possibility of a "mix" occurring when the materials are
weighed out at the pottery supply dealer's shop. Most of our materials
are white powders and are impossible to tell from each other by
appearance. Always test new purchases of materials in a 100 or 200 gram
batch changing only one material at a time. And, of course, buy full
bags whenever you possibly can and keep or record the information on
lot and mine or manufacturer that is printed on the bag.
5. Different firing temperatures can cause glazes to look significantly
different. Always use cones on every shelf in every firing.
6. Lastly there is always the possibility of potter error in mixing the
glaze. I would be particularly concerned working in a community studio
where you don't know how careful the person is who mixed the last batch.
Well, I hope all this helps. It was an interesting, yet frustrating
excercise. I started from the point of view that I would probably find
a smoking gun or two--but it/they just weren't there.
I am still open to testing an occasional batch if someone really thinks
they have found a bad lot. Let me know.
Regards,
John
http://www.frogpondpottery.com
http://www.masteringglazes.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.
Ruth Ballou on fri 18 apr 03
Hi John,
I've mixed Spearmint for the community studio where I teach. The
problem I've found with the new copper carbonate is one that does not
show up in a small sample. The new bright green copper carbonate
settles out very quickly. The larger the bucket of glaze, the bigger
the problem. Mixing must be enthusiastic and frequent for the copper to
stay suspended. The copper can drop to the bottom of the bucket between
one dip and the next, which means that over time, the glaze contains
progressively greater amounts of copper. Pots glazed when the bucket is
nearing empty are significantly greener than those glazed at the
beginning. This may have implications for your copper leaching values.
In addition, the new copper is worthless for rubbing into textured
areas. It powders off immediately. We have switched to a slip for this
effect.
Hope this is informative.
Ruth Ballou
Silver Spring, MD (Where it's rainy and cold, just like Brussels is
supposed to be, which is warm and sunny instead.)
On Friday, April 18, 2003, at 12:17 PM, John Hesselberth wrote:
> Hi Everyone,
>
> As many of you know, I have been trying to track down what differences
> there might be in the copper carbonates, cobalt carbonates, and rutiles
> being offered for sale by pottery supply dealers. In other words, are
> there any "bad" lots of these things being sold.
>
> The bottom line is that I haven't been able to find any bad stuff among
> these three ingredients. I offer considerable detail on my experiments
> below and some hypotheses on what may be going on with people who are
> reporting trouble.
>
> First, copper carbonate
>
> I have obtained copper carbonate samples from Axner, U.S. Pigments,
> DelVal (Judy Wilson at DelVal has been my supplier for about 10 years
> and I've never had any question about the quality of the materials she
> sells) plus one sample sent to me with the supplier not identified (but
> it was from the northeast U.S.). I also still have some of the "old"
> grey-green copper carbonate that I bought from DelVal 2 or 3 years ago.
>
> Some comments I picked up from the various suppliers I talked to.
> There is considerable consolidation going on in the manufacture of
> copper carbonate. If we are not already down to 1 manufacturer we may
> be soon. Our direct suppliers started switching to the new, brighter
> green material 1-2 years ago because they were either having trouble
> with their current supplier or they could no longer get the old
> material. I would guess there are still at least 2 manufacturers in
> the system judging from the color of the materials I tested (or 2
> different grades or mesh sizes)--anyhow the new materials are not all
> identical in appearance of the powder.
>
> I put these samples of copper carbonate into Spearmint--one of the
> glazes in Mastering Cone 6 Glazes which is a bit color-fussy. For those
> who haven't seen it, it is a cool green and some people have reported
> getting a more yellowy green than we show in the book--more on that in
> a minute. When I compared these various copper carbonates (using the
> same rutile and all other ingredients) on the same clay body, I could
> see only the tiniest of differences. If anything (and I am really
> picking at nits here) the original grey-green copper gave a slightly
> yellower green in the fired glaze.
>
> The biggest difference was dependent on the clay body it was on. I used
> a grolleg porcelain, a white stoneware and a tan stoneware. This is a
> fairly opaque glaze and the white stoneware and the tan stoneware
> samples were quite similar--although a little bit of the clay color
> influenced the final color of the fired glaze. The porcelain samples
> matched the color of the glaze in the book pretty well. This glaze is
> significantly different looking on porcelain vs. stoneware and that may
> account for some of the problems people are having reproducing the
> color in the book. Apparently that extra neph sy that is in a typical
> cone 6 porcelain body had quite an effect--at least on this particular
> glaze. I still wouldn't call the stoneware samples a "yucky
> yellow-green". Rather they were slightly darker and greyer than the
> porcelain samples with more body color showing through where the glaze
> was thin.
>
> Anyhow I conclude there is nothing wrong with the brighter green copper
> carbonate we are now buying. It gave fully equivalent results to the
> older material. That is not to say there might not be a bad lot
> running around or a supplier who is buying a significantly less pure
> grade of the material--there might be, but I saw no evidence of it.
>
> On to cobalt carbonate
>
> I obtained cobalt carbonate from DelVal, Axner, U.S. Pigments, and 2
> samples from the northeast U.S. One of those 2 samples was distinctly
> a very grey-lavender instead of the normal bright lavender we are used
> to. I thought I might have a smoking gun here. Of the ones that were
> in the bright lavender family some were less bright (more white) than
> others so there are obviously still some multiples sources and/or
> grades of cobalt in our system.
>
> I put the cobalt carbonate samples into Semimatte Base 2 (from MC6G, of
> course) at a 1% level along with 6% rutile (I just love that stuff--I
> put it in everything). I only used white and tan stoneware for these
> samples. Again, no discernible difference in fired glaze
> color--nothing that couldn't be explained by slight variation in
> thickness of application. Even the grey-lavender sample seemed to be
> fine.
>
> So again, if there is any "bad" cobalt in the system I have yet to find
> it.
>
> Now rutile
>
> I had more samples of rutile because several of our suppliers carry
> more than one grade. I had dark and regular rutile from DelVal (the
> dark is several years old and Judy can no longer get it from her
> supplier), ceramic light from Axner, ceramic-and ceramic-lite grades
> from U.S. Pigments, a regular rutile from the unidentified supplier,
> and a dark rutile from Portland Pottery Supply--South (used to be Corey
> Ceramics--they are in Mass) (Pat says she can still get this from her
> supplier if anyone is interested) -- 7 samples in all. I used
> Spearmint to test these with DelVal "old" copper carbonate in all
> samples. Again I tested only on white and tan stoneware.
>
> These various rutiles were quite different in color of the powder
> varying from a light tan to medium brown. But again only the tiniest
> differences in fired glaze colors. I may not be using a glaze where
> rutile is critical to color--some of you may remember a post by Richard
> Aerni a couple years ago where he described what he had learned about
> the various grades of rutile and how important it was to him to get the
> "right" one for his glaze--but I just could not see any differences
> worth talking about. I would add, though, that I did have one or two
> samples on porcelain through this process and there were slightly
> bigger difference there. The number of samples was too small to be
> certain, but I may rerun this test with a full porcelain set sometime
> in the future.
>
> Sooooo, what's going on???
>
> I would speculate that some of us are seeing 1 of several things when
> we are suspicious of "bad" materials and not getting glaze colors we
> expected:
>
> 1. There still could be some bad copper, cobalt, or rutile out there
> and I just haven't found it.
>
> 2. Thickness of application can make a big difference in the appearance
> of a fired glaze.
>
> 3. These tests brought home again to me how different a glaze can look
> on different clay bodies--particularly stoneware vs. porcelain in my
> tests.
>
> 4. When we buy materials in less than full bag lots, there is a
> definite possibility of a "mix" occurring when the materials are
> weighed out at the pottery supply dealer's shop. Most of our materials
> are white powders and are impossible to tell from each other by
> appearance. Always test new purchases of materials in a 100 or 200 gram
> batch changing only one material at a time. And, of course, buy full
> bags whenever you possibly can and keep or record the information on
> lot and mine or manufacturer that is printed on the bag.
>
> 5. Different firing temperatures can cause glazes to look significantly
> different. Always use cones on every shelf in every firing.
>
> 6. Lastly there is always the possibility of potter error in mixing the
> glaze. I would be particularly concerned working in a community studio
> where you don't know how careful the person is who mixed the last
> batch.
>
> Well, I hope all this helps. It was an interesting, yet frustrating
> excercise. I started from the point of view that I would probably find
> a smoking gun or two--but it/they just weren't there.
>
> I am still open to testing an occasional batch if someone really thinks
> they have found a bad lot. Let me know.
>
> Regards,
>
> John
>
> http://www.frogpondpottery.com
> http://www.masteringglazes.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.
>
>
Ruth Ballou
Silver Spring, MD
John Hesselberth on fri 18 apr 03
Hi Ruth,
You are right. I might not see that in a small test; however I did rub
a little of each material between my fingers. In that very crude test I
judged the new material to be at least as fine a mesh as my original.
I have also examined the glaze slop after it sat for 24 hours and saw
no evidence of settling--at least not like a manganese
dioxide-containing glaze does. Maybe there is a larger mesh size lot
out there someplace. Did you get yours at Clayworks in Baltimore?
John
On Friday, April 18, 2003, at 02:56 PM, Ruth Ballou wrote:
> Hi John,
>
> I've mixed Spearmint for the community studio where I teach. The
> problem I've found with the new copper carbonate is one that does not
> show up in a small sample. The new bright green copper carbonate
> settles out very quickly. The larger the bucket of glaze, the bigger
> the problem. Mixing must be enthusiastic and frequent for the copper to
> stay suspended. The copper can drop to the bottom of the bucket between
> one dip and the next, which means that over time, the glaze contains
> progressively greater amounts of copper. Pots glazed when the bucket is
> nearing empty are significantly greener than those glazed at the
> beginning. This may have implications for your copper leaching values.
>
> In addition, the new copper is worthless for rubbing into textured
> areas. It powders off immediately. We have switched to a slip for this
> effect.
>
> Hope this is informative.
>
> Ruth Ballou
> Silver Spring, MD (Where it's rainy and cold, just like Brussels is
> supposed to be, which is warm and sunny instead.)
>
>
> On Friday, April 18, 2003, at 12:17 PM, John Hesselberth wrote:
>
>> Hi Everyone,
>>
>> As many of you know, I have been trying to track down what differences
>> there might be in the copper carbonates, cobalt carbonates, and
>> rutiles
>> being offered for sale by pottery supply dealers. In other words, are
>> there any "bad" lots of these things being sold.
>>
>> The bottom line is that I haven't been able to find any bad stuff
>> among
>> these three ingredients. I offer considerable detail on my
>> experiments
>> below and some hypotheses on what may be going on with people who are
>> reporting trouble.
>>
>> First, copper carbonate
>>
>> I have obtained copper carbonate samples from Axner, U.S. Pigments,
>> DelVal (Judy Wilson at DelVal has been my supplier for about 10 years
>> and I've never had any question about the quality of the materials she
>> sells) plus one sample sent to me with the supplier not identified
>> (but
>> it was from the northeast U.S.). I also still have some of the "old"
>> grey-green copper carbonate that I bought from DelVal 2 or 3 years
>> ago.
>>
>> Some comments I picked up from the various suppliers I talked to.
>> There is considerable consolidation going on in the manufacture of
>> copper carbonate. If we are not already down to 1 manufacturer we may
>> be soon. Our direct suppliers started switching to the new, brighter
>> green material 1-2 years ago because they were either having trouble
>> with their current supplier or they could no longer get the old
>> material. I would guess there are still at least 2 manufacturers in
>> the system judging from the color of the materials I tested (or 2
>> different grades or mesh sizes)--anyhow the new materials are not all
>> identical in appearance of the powder.
>>
>> I put these samples of copper carbonate into Spearmint--one of the
>> glazes in Mastering Cone 6 Glazes which is a bit color-fussy. For
>> those
>> who haven't seen it, it is a cool green and some people have reported
>> getting a more yellowy green than we show in the book--more on that in
>> a minute. When I compared these various copper carbonates (using the
>> same rutile and all other ingredients) on the same clay body, I could
>> see only the tiniest of differences. If anything (and I am really
>> picking at nits here) the original grey-green copper gave a slightly
>> yellower green in the fired glaze.
>>
>> The biggest difference was dependent on the clay body it was on. I
>> used
>> a grolleg porcelain, a white stoneware and a tan stoneware. This is a
>> fairly opaque glaze and the white stoneware and the tan stoneware
>> samples were quite similar--although a little bit of the clay color
>> influenced the final color of the fired glaze. The porcelain samples
>> matched the color of the glaze in the book pretty well. This glaze is
>> significantly different looking on porcelain vs. stoneware and that
>> may
>> account for some of the problems people are having reproducing the
>> color in the book. Apparently that extra neph sy that is in a typical
>> cone 6 porcelain body had quite an effect--at least on this particular
>> glaze. I still wouldn't call the stoneware samples a "yucky
>> yellow-green". Rather they were slightly darker and greyer than the
>> porcelain samples with more body color showing through where the glaze
>> was thin.
>>
>> Anyhow I conclude there is nothing wrong with the brighter green
>> copper
>> carbonate we are now buying. It gave fully equivalent results to the
>> older material. That is not to say there might not be a bad lot
>> running around or a supplier who is buying a significantly less pure
>> grade of the material--there might be, but I saw no evidence of it.
>>
>> On to cobalt carbonate
>>
>> I obtained cobalt carbonate from DelVal, Axner, U.S. Pigments, and 2
>> samples from the northeast U.S. One of those 2 samples was distinctly
>> a very grey-lavender instead of the normal bright lavender we are used
>> to. I thought I might have a smoking gun here. Of the ones that were
>> in the bright lavender family some were less bright (more white) than
>> others so there are obviously still some multiples sources and/or
>> grades of cobalt in our system.
>>
>> I put the cobalt carbonate samples into Semimatte Base 2 (from MC6G,
>> of
>> course) at a 1% level along with 6% rutile (I just love that stuff--I
>> put it in everything). I only used white and tan stoneware for these
>> samples. Again, no discernible difference in fired glaze
>> color--nothing that couldn't be explained by slight variation in
>> thickness of application. Even the grey-lavender sample seemed to be
>> fine.
>>
>> So again, if there is any "bad" cobalt in the system I have yet to
>> find
>> it.
>>
>> Now rutile
>>
>> I had more samples of rutile because several of our suppliers carry
>> more than one grade. I had dark and regular rutile from DelVal (the
>> dark is several years old and Judy can no longer get it from her
>> supplier), ceramic light from Axner, ceramic-and ceramic-lite grades
>> from U.S. Pigments, a regular rutile from the unidentified supplier,
>> and a dark rutile from Portland Pottery Supply--South (used to be
>> Corey
>> Ceramics--they are in Mass) (Pat says she can still get this from her
>> supplier if anyone is interested) -- 7 samples in all. I used
>> Spearmint to test these with DelVal "old" copper carbonate in all
>> samples. Again I tested only on white and tan stoneware.
>>
>> These various rutiles were quite different in color of the powder
>> varying from a light tan to medium brown. But again only the tiniest
>> differences in fired glaze colors. I may not be using a glaze where
>> rutile is critical to color--some of you may remember a post by
>> Richard
>> Aerni a couple years ago where he described what he had learned about
>> the various grades of rutile and how important it was to him to get
>> the
>> "right" one for his glaze--but I just could not see any differences
>> worth talking about. I would add, though, that I did have one or two
>> samples on porcelain through this process and there were slightly
>> bigger difference there. The number of samples was too small to be
>> certain, but I may rerun this test with a full porcelain set sometime
>> in the future.
>>
>> Sooooo, what's going on???
>>
>> I would speculate that some of us are seeing 1 of several things when
>> we are suspicious of "bad" materials and not getting glaze colors we
>> expected:
>>
>> 1. There still could be some bad copper, cobalt, or rutile out there
>> and I just haven't found it.
>>
>> 2. Thickness of application can make a big difference in the
>> appearance
>> of a fired glaze.
>>
>> 3. These tests brought home again to me how different a glaze can look
>> on different clay bodies--particularly stoneware vs. porcelain in my
>> tests.
>>
>> 4. When we buy materials in less than full bag lots, there is a
>> definite possibility of a "mix" occurring when the materials are
>> weighed out at the pottery supply dealer's shop. Most of our materials
>> are white powders and are impossible to tell from each other by
>> appearance. Always test new purchases of materials in a 100 or 200
>> gram
>> batch changing only one material at a time. And, of course, buy full
>> bags whenever you possibly can and keep or record the information on
>> lot and mine or manufacturer that is printed on the bag.
>>
>> 5. Different firing temperatures can cause glazes to look
>> significantly
>> different. Always use cones on every shelf in every firing.
>>
>> 6. Lastly there is always the possibility of potter error in mixing
>> the
>> glaze. I would be particularly concerned working in a community
>> studio
>> where you don't know how careful the person is who mixed the last
>> batch.
>>
>> Well, I hope all this helps. It was an interesting, yet frustrating
>> excercise. I started from the point of view that I would probably
>> find
>> a smoking gun or two--but it/they just weren't there.
>>
>> I am still open to testing an occasional batch if someone really
>> thinks
>> they have found a bad lot. Let me know.
>>
>> Regards,
>>
>> John
>>
>> http://www.frogpondpottery.com
>> http://www.masteringglazes.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.
>>
>>
> Ruth Ballou
> Silver Spring, MD
>
> _______________________________________________________________________
> _______
> 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.
>
>
http://www.frogpondpottery.com
http://www.masteringglazes.com
John Hesselberth on fri 18 apr 03
On Friday, April 18, 2003, at 02:51 PM, Jim Kasper wrote:
> John,
> What about cobolt oxide and copper oxide? Also why use the
> carbonates
> instead of oxides?
> Regards,
> Jim
Hi Jim,
I know nothing about those. I have always used the carbonates. I
seriously doubt if it makes much difference. If you do use the oxides
make sure you get black copper oxide instead of red or be prepared to
use a surfactant to get it to disperse. It is a pain.
John
http://www.frogpondpottery.com
http://www.masteringglazes.com
Ruth Ballou on fri 18 apr 03
Hi John,
You're correct. Our batch was supplied by Clayworks in Baltimore. We
also called all around looking for the old stuff. A couple of suppliers
assured us that they had the good stuff. Upon receipt, it proved to be
the new, bright green copper. By the way, just to make sure we're
talking about the same thing, does yours have a grainy texture? It
reminds me of the stuff used in the sand painting craze a few years
ago. Do you think it's just mesh size? Has anyone tried ball milling?
That's one piece of equipment I don't have.
I'm glad I accidentally doubled an order of copper carbonate a few
years ago. You just never know when a material is going to go south on
you.
Ruth Ballou
Silver Spring, MD
On Friday, April 18, 2003, at 04:38 PM, John Hesselberth wrote:
> Hi Ruth,
>
> You are right. I might not see that in a small test; however I did rub
> a little of each material between my fingers. In that very crude test I
> judged the new material to be at least as fine a mesh as my original.
> I have also examined the glaze slop after it sat for 24 hours and saw
> no evidence of settling--at least not like a manganese
> dioxide-containing glaze does. Maybe there is a larger mesh size lot
> out there someplace. Did you get yours at Clayworks in Baltimore?
>
> John
>
>
Cindy Gatto on fri 18 apr 03
Hi to all,
I would like to make a comment on this because I did find a bad source of
cobalt carb. Several months ago I posted something about this asking if
anyone ever had the same problem I was having and someone did. [I do not
remember who] I bought cobalt carb from U.S. Pigment at a great price of
$19.00 a pound if I bought 10 lbs. It was that greyish lavender color you
mentioned. It is very weak! If I use it I have to just about double it to get
the same strength as the cobalt carb I get from my regular supplier . So I
guess I have to disagree with you John there are differences depending on
where you get it from. Be careful when you think you are getting a good deal
you usually get what you pay for!
Cindy Gatto/The Mudpit
228 Manhattan Ave
Brooklyn, NY. 11206
www.mudpitnyc.com
John Hesselberth on fri 18 apr 03
No. Mine is quite fine and smooth. Feels almost like talcum powder. We
must have different stuff.
John
On Friday, April 18, 2003, at 05:46 PM, Ruth Ballou wrote:
> By the way, just to make sure we're
> talking about the same thing, does yours have a grainy texture?
http://www.frogpondpottery.com
http://www.masteringglazes.com
Ababi on sat 19 apr 03
You might see it as an advantage ( So I do)
When I want a glaze with 0.5% cobalt oxide: Fine
But when I want a glaze with 0.1 cobalt oxide? How can I test it? I use instead 0.3, 0.5
cobalt carbonate
Ababi Sharon
Glaze addict
Kibbutz Shoval Israel
ababisha@shoval.org.il
http://members4.clubphoto.com/ababi306910/
http://www.milkywayceramics.com/cgallery/asharon.htm
and also
http://www.israel-ceramics.org/membersGallery/personalpage.asp?MID=507
---------- Original Message ----------
>Hi to all,
>I would like to make a comment on this because I did find a bad source of
>cobalt carb. Several months ago I posted something about this asking if
>anyone ever had the same problem I was having and someone did. [I do not
>remember who] I bought cobalt carb from U.S. Pigment at a great price of
>$19.00 a pound if I bought 10 lbs. It was that greyish lavender color you
>mentioned. It is very weak! If I use it I have to just about double it to get
>the same strength as the cobalt carb I get from my regular supplier . So I
>guess I have to disagree with you John there are differences depending on
>where you get it from. Be careful when you think you are getting a good deal
>you usually get what you pay for!
>Cindy Gatto/The Mudpit
>228 Manhattan Ave
>Brooklyn, NY. 11206
>www.mudpitnyc.com
David Hewitt on sat 19 apr 03
John,
You must have done quite a lot of work to produce these answers. Thank
you for sharing your results with us.
As a matter of interest, did you get an analysis from each of the
suppliers for each material and, if so, did this show that each cooper
carbonate, cobalt carbonate and rutile were the same?
When I have had problems, such as with black iron oxide and talc, I have
eventually found that the reason was that the analysis was quite
different.
The point being is, that if the analyses for two different copper
carbonates, etc., are the same then one would expect the same results.
What I would like to see is analysis sheets being much more readily
available to the customer.
David
John Hesselberth writes
>Hi Everyone,
>
>As many of you know, I have been trying to track down what differences
>there might be in the copper carbonates, cobalt carbonates, and rutiles
>being offered for sale by pottery supply dealers. In other words, are
>there any "bad" lots of these things being sold.
>
>The bottom line is that I haven't been able to find any bad stuff among
>these three ingredients. I offer considerable detail on my experiments
>below and some hypotheses on what may be going on with people who are
>reporting trouble.
>
--
David Hewitt
David Hewitt Pottery
7 Fairfield Road, Caerleon, Newport,
South Wales, NP18 3DQ.
Tel:- +44 (0) 1633 420647
Fax:- +44 (0) 870 1617274
Web:- http://www.dhpot.demon.co.uk
Ruth Ballou on sat 19 apr 03
John,
Ok, maybe I should send you a sample of this one.... This is all we've
been able to find among all the suppliers we've called, so I assumed
(in error, it seems) that it was the same as yours. I've deleted your
first post... Who did you say your supplier is?
If you're interested in seeing this, send me your address and I'll pack
up a sample when I can get back into the studio on Monday.
Ruth Ballou
Silver Spring, MD (where blossoming dogwoods foil the cool grayness)
On Friday, April 18, 2003, at 07:48 PM, John Hesselberth wrote:
> No. Mine is quite fine and smooth. Feels almost like talcum powder. We
> must have different stuff.
>
> John
> On Friday, April 18, 2003, at 05:46 PM, Ruth Ballou wrote:
>
>> By the way, just to make sure we're
>> talking about the same thing, does yours have a grainy texture?
> http://www.frogpondpottery.com
> http://www.masteringglazes.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.
>
>
Ruth Ballou
Silver Spring, MD
Ellie Blair on sat 19 apr 03
I was taught that the only difference between the oxide and the carbonate is
the strength. You need to add more of the carbonate than the oxide. We did
tests to determine what the ratio was going to be per glaze recipe.
Ellie B.
----- Original Message -----
From: "John Hesselberth"
To:
Sent: Friday, April 18, 2003 3:29 PM
Subject: Re: Copper, cobalt, and rutile (long)
> On Friday, April 18, 2003, at 02:51 PM, Jim Kasper wrote:
>
> > John,
> > What about cobolt oxide and copper oxide? Also why use the
> > carbonates
> > instead of oxides?
> > Regards,
> > Jim
>
> Hi Jim,
>
> I know nothing about those. I have always used the carbonates. I
> seriously doubt if it makes much difference. If you do use the oxides
> make sure you get black copper oxide instead of red or be prepared to
> use a surfactant to get it to disperse. It is a pain.
>
> John
>
> http://www.frogpondpottery.com
> http://www.masteringglazes.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.
>
John Hesselberth on sat 19 apr 03
On Friday, April 18, 2003, at 11:51 PM, Marcia Selsor wrote:
> My new question is in regards to CROCUS MARTIS. I prdered some from
> Seattle Pottery and they sent Spanish Red iron which they said was the
> same thing. Clayart Center mentions it is the same thing on their
> website. Hamer and Hamer says it is Anhydrous Iron Sulphate (I think
> that was the correct description) which means it is a salt, I believe.
> I
> was able to get some after a search from a supplier in Portland, Maine.
> I knew Crocus Martis many years ago. I am surprised itn is being passed
> off now as an equivalent to Spanish Iron Oxide. Am I missing something
> here? Crocus Martis is used in Over glaze decoration on Tin Glaze.
> Is it really the same as Spanish Iron Oxide. I am skeptical
Hi Marcia,
I'm glad Caribbean Sea Green finally turned green for you. How much
rutile did it take?
With respect to crocus martis and Spanish Red Iron Oxide, I think you
just opened a can of worms. Here are a couple sentences from Tony
Hansen's site that say it well re crocus martis:
> There are varying ideas from country to country about what this
> material is. Historically it was just a naturally-occurring red iron
> oxide containing impurities (i.e. clay minerals) or an ultra-high iron
> clay. Today, Crocus Martis sold by ceramic suppliers is more likely to
> be a soluble synthetic impure red iron sulphate or a calcined-at-900C
> version of the sulphate (it is insoluble)
and here, from a Clayart post in 1998 is what Steve Grimmer (quoting
Tom Buck) had to say about Spanish Red Iron Oxide:
>
> According to Tom Buck in a post off-list, Spanish Iron is an
> extremely pure form of iron oxide. It is produced as a byproduct of
> a particular bacteria in ferrous sulphate, of all things. Regular red
> iron oxide can contain any number of impurities, including
> silicates and metallic iron. It's not as pure. Did I misunderstand
> you, Tom?
So they both apparently have a connection to iron sulfate--or at least
may. Are they the same? Beats me. I bet Tom Buck will chime in on
this one again. Tom?
http://www.frogpondpottery.com
http://www.masteringglazes.com
John Hesselberth on sat 19 apr 03
On Saturday, April 19, 2003, at 11:46 AM, David Hewitt wrote:
> As a matter of interest, did you get an analysis from each of the
> suppliers for each material and, if so, did this show that each cooper
> carbonate, cobalt carbonate and rutile were the same?
Hi David,
Well, I tried. I was successful about 50% of the time. Or partially
successful. One analysis I got was obviously just pulled from a file
because it was dated 1979. But what do you do when the person says
"Well that's the only one I have--It hasn't changed since then"?
Analyses for rutile were the toughest to come by. Usually I was just
sent the MSDS which are nearly useless for this purpose. Judy Wilson's
staff at Del Val were the only ones who really helped me track down an
actual analysis for rutile and Judy herself go me one for cobalt
carbonate (and later for the spodumene she carries).
I agree that more pottery supply dealers should keep a file of these on
hand, but until more of us start asking for them it is a bit like
pulling teeth. Unfortunately there are usually 3 or 4 steps in the
distribution chain before the material gets to a pottery supply dealer
so each step in that chain sometimes has to be tracked down to get an
relevant analysis. The ones I did get didn't show me any differences
worth talking about, but given what I was able to get, who knows?
Regards,
John
http://www.frogpondpottery.com
http://www.masteringglazes.com
John Hesselberth on sat 19 apr 03
I need to add one bit of information to the response I sent a few hours
ago to David Hewitt's post. Soon after I sent that post, I opened a
package I had received from Sheffield Pottery in Mass. A few days
before I had a conversation with Delores at Sheffield on a different
subject. In the course of that conversation, I had bemoaned how
difficult it was to get analysis sheets for the coppers, cobalts and
rutiles I had been testing. Delores offered to get me theirs and there
they were in that package! Detailed analyses for 2 types of rutile,
their copper carbonate and their cobalt carbonate. Thank you Delores
and Sheffield!
If there are other pottery supply dealers who either keep an up-to-date
file of analyses or can/will get them promptly, please let us know.
More and more of us are interested in this every day.
Regards,
John
>
http://www.frogpondpottery.com
http://www.masteringglazes.com
Sandy Henderson on sun 20 apr 03
Hi, John -- I have had the same problems with copper carbonate as Ruth Ballou has. My previous batch (bought as I recall from Great Lakes Clay) settled out so fast I had to stir vigorously between dipping each pot. I just bought some from Bailey and it is much easier to work with. The green -- in your Spearmint glaze -- also seems brighter, but maybe that is because the copper stays suspended better.
Sandy Henderson in Northwest Indiana
Ron Roy on sun 20 apr 03
I only use carbonates for two reasons - first of all they are different
colours - the oxides are both black and I want to be able to see the
difference whan I can.
The carbonates tend to diffuse better in glaze because of smaller particle size.
RR
>John,
> What about cobolt oxide and copper oxide? Also why use the carbonates
>instead of oxides?
>Regards,
>Jim
>
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on sun 20 apr 03
Hi David,
Frankly I just don't trust suppliers to do this part right - perhaps I will
learn to trust them in the future if they start taking the job seriously.
I now deal directly with the mines - at least the suppliers can sometimes
get that part right - like the address and phone #. Some mines have their
own web site and post current information on all their products - I have
had satisfactory replies from all the mines I have contacted - all have fax
machines.
The best way to deal with the supplier is ask them to get a current
analysis - easy for them to do that. Just don't expect that analysis to
match the materials you have if they are old - - if they would only put
batch numbers on the lots and match the analysis to those batches.
The best situation is when the mine supplies an analysis with the shipment
- the way it should be.
The Felspar Corporation website is a joy to see - G200 and EPK are two of
their products - and two of the best materials you can buy - they ship
analysis with their product - nothing to hide - top quality - I know cause
Tuckers tests the EPK.
I asked a frit maker once - which spar they used - answer was G200 - why -
it's consistent compared to others. Not a comment on the mine but on the
deposit.
We tend to think the materials we use are close to the same each time -
well not so in most cases. Lucky for us - most of the time - it is not that
crucial. Still - a good argument for having a variety of materials in
bodies and glazes. Those of you who like glazes and bodies with 3 or 4
ingredients - well good luck.
We have a long way to go in this area - the more we bug our suppliers the
better off we will be - and that means better business for them too.
RR
>You must have done quite a lot of work to produce these answers. Thank
>you for sharing your results with us.
>
>As a matter of interest, did you get an analysis from each of the
>suppliers for each material and, if so, did this show that each cooper
>carbonate, cobalt carbonate and rutile were the same?
>
>When I have had problems, such as with black iron oxide and talc, I have
>eventually found that the reason was that the analysis was quite
>different.
>
>The point being is, that if the analyses for two different copper
>carbonates, etc., are the same then one would expect the same results.
>What I would like to see is analysis sheets being much more readily
>available to the customer.
>
>David
>
>John Hesselberth writes
>>Hi Everyone,
>>
>>As many of you know, I have been trying to track down what differences
>>there might be in the copper carbonates, cobalt carbonates, and rutiles
>>being offered for sale by pottery supply dealers. In other words, are
>>there any "bad" lots of these things being sold.
>>
>>The bottom line is that I haven't been able to find any bad stuff among
>>these three ingredients. I offer considerable detail on my experiments
>>below and some hypotheses on what may be going on with people who are
>>reporting trouble.
>>
>
>--
>David Hewitt
>David Hewitt Pottery
>7 Fairfield Road, Caerleon, Newport,
>South Wales, NP18 3DQ.
>Tel:- +44 (0) 1633 420647
>Fax:- +44 (0) 870 1617274
>Web:- http://www.dhpot.demon.co.uk
>
>______________________________________________________________________________
>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
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Tony Hansen on mon 21 apr 03
I just got a load of ware out of the kiln using
Kats Bombproof Ravenscrag recipe with cobalt.
I have about 20 pieces and half were oxide and
half carbonate. The oxide ones were much nicer,
not just because the color was darker, but since
the particle size is larger, the glaze was more
variegated, much more interesting. The carbonate
ones also have minute pinholes, I assume from the
gases being expelled, which the oxide does not have.
> Hi, John -- I have had the same problems with copper carbonate as Ruth Ballou has. My previous batch (bought as I recall from Great Lakes Clay) settled out so fast I had to stir vigorously between dipping each pot. I just bought some from Bailey and it is much easier to work with. The green -- in your Spearmint glaze -- also seems brighter, but maybe that is because the copper stays suspended better.
========
Tony Hansen
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