vikki dow on thu 22 apr 99
Hi Clayart buds,
I have a fun glaze puzzle for those of you that enjoy figuring out the
mysteries of this art. The reason that I use the word fun is because this
time my glaze surprise was a good one and the new color is one of my best
sellers.
Ok here it is. I fire an electric kiln to ^9-10, my clay body is B-mix.
The glaze that I have a question about is Laguna's Iron Red. Because I
fire an electric klin to ^9-10 the elements burn out relatively quick and
on one occassion when the kiln only got to about ^8 1/2, I closed the the
lid on the damn thing and fired it up as hot as it would go, ^7 ,and let it
soak for an hour and a half. I opened the kiln after it had cooled and
discovered that I had a marvelous rich burgundy color, with a satin matt
finish. Does anyone know why this happens? The iron red and the burgundy
are both a red but I get two wonderful glazes for the price of one, other
than the fact that I have to glaze fire one twice. Does anyone know how I
might get this color without firing twice ? I think we had a glaze called
Ox blood that was similar when I was in school, but we fired it in a gas
kiln.
Thanks for any help !
Go Well
Libby, at Stilltree Pottery
John Baymore on sat 24 apr 99
------------------
(snip)
. . . .. .. ... ............Because I fire an electric klin to =5E9-10 the
elements burn out relatively quick and on one occassion when the kiln only
got to about =5E8 1/2, I closed the the
lid on the damn thing and fired it up as hot as it would go, =5E7 ,and let =
it
soak for an hour and a half. I opened the kiln after it had cooled and
discovered that I had a marvelous rich burgundy color, with a satin matt
finish. Does anyone know why this happens?
(clip)
Libby,
Not a lot of detail in your post.... but I think I have the basics enough
to make a semi-educated guess. (All my opinions are semi-educated =3Cg=3E.)
First of all the glaze is a little underfired since it is a cone 9 only
going to 8 1/2. That could amount to some of the dryer surface all by
itself, particularly if the glaze is formulated such that it is particular
about the end cone to start with (narrow range). Since this is only 1/2
cone difference however, the second firing could have resulted in enough
total heat work to fully mature the glaze during the second firing. Let's
assume that it did.
The glaze you have is saturated with iron oxide. It is also probably
oversupplied with another oxide that likes to come out of the glass melt.
The second firing with the long soak at cone 7 ish gave the glaze time to
percipitate out some form of crystaline silicate type thing in tiny
micro-crystals floating on the surface of the glaze. These crystals are
stained by some of the iron oxide in the glaze (which is also in
oversupply) Because they are on the surface they change the glaze surface
to a semi-matte. Because the iron is staining a crystal, not glass, the
tone of the color produced is different. Because only some of the iron is
staining the crystal (the rest is still in the glass underneath) the tone
of the color is different.
To try to accomplish this again fire the glaze up to the normal end cone
you reached the first time, then cool down to cone 7, and then soak for
about the same time or a little longer than you did the last time. Should
be similar. Experiment with soak times.
Electric kilns are notorious for fast cooling, which limits microcrystaline
sufrace effects on glazes. One of the main differences between pieces
fired in large, thick walled, heavy thermal mass gas kilns and hobby type
electric kilns is the rate of cooling.... not oxidation versus reduction.
Try firing down on your electric with all of your glazes. You may be
suprised.
This is a piece of cake if you have a digital controller.
Hope this is in the right ballpark. I am sure you'll hear from others.
BEst,
..........................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752
JBaymore=40Compuserve.com
Jocelyn McAuley on fri 28 mar 03
Hi Janet,
I'm leaning towards focusing on the fact that your resulting glaze is a
crawler...
maybe check out the order in which you store your glaze chemicals, and see
what is next to the ingredients in the recipe. Magnesium carbonate is
used in large percentages to produce crawling glazes. It's use in your
glaze (instead of nephaline syenite?) would also explain the purple color
from cobalt.
good luck!
On Fri, 28 Mar 2003, Janet Moe / Paul Bailey wrote:
> I made a test batch of the following recipe. It came out purple with
> crawling. Very nice! A friend also made a test batch. It came out green
> as it should. Now I am wondering what I used? I was convinced I mixed it
> properly with the correct materials but obviously not. Any ideas? TIA
>
> Reitz Green - Cone 10 Reduction
>
> 70
> Nepheline Syenite
> 5 Calcium Carbonate
> 2 Gerstley Borate
> 15
> Petalite
> 8 EPK
> ____
> 100
>
> 1 Cobalt Carbonate
> 2 Rutile
>
> Janet, Denman Island, British Columbia
>
> ______________________________________________________________________________
> 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.
>
--
Jocelyn McAuley ><<'> jocie@worlddomination.net
Eugene, Oregon http://www.ceramicism.com
David Hendley on fri 28 mar 03
Reitz Green is a well-known and well-tested glaze that does indeed
come out green where thick and dark gray to black where thin.
The green color does come from cobalt, which, in the presence
of titanium (rutile), in the right glaze formula, will be green rather
than blue.
A purple color from cobalt suggests that magnesium is present in
the glaze. The most common ingredient to induce crawling in
a glaze is magnesium carbonate. Therefore, I would bet that you
mistakenly used "magnesium carbonate", not "calcium carbonate"
when you mixed your glaze test.
David Hendley
Maydelle, Texas
david@farmpots.com
http://www.farmpots.com
----- Original Message -----
> I made a test batch of the following recipe. It came out purple with
> crawling. Very nice! A friend also made a test batch. It came out green
> as it should. Now I am wondering what I used? I was convinced I mixed it
> properly with the correct materials but obviously not. Any ideas? TIA
>
> Reitz Green - Cone 10 Reduction
>
> 70
> Nepheline Syenite
> 5 Calcium Carbonate
> 2 Gerstley Borate
> 15
> Petalite
> 8 EPK
> ____
> 100
>
> 1 Cobalt Carbonate
> 2 Rutile
>
Janet Moe / Paul Bailey on fri 28 mar 03
I made a test batch of the following recipe. It came out purple with
crawling. Very nice! A friend also made a test batch. It came out green
as it should. Now I am wondering what I used? I was convinced I mixed it
properly with the correct materials but obviously not. Any ideas? TIA
Reitz Green - Cone 10 Reduction
70
Nepheline Syenite
5 Calcium Carbonate
2 Gerstley Borate
15
Petalite
8 EPK
____
100
1 Cobalt Carbonate
2 Rutile
Janet, Denman Island, British Columbia
Marcia Selsor on fri 28 mar 03
I believe Reitz Green has copper in it instead of Cobalt.
I'd have to check my notebook at the shop.
just an instinct.Often people write down abbreviation co for both cobalt
and copper. cu is the proper chemical symbol for copper. I do think
there was a similar error in Ron and John's book listing the recipe for
carribean green and listing cobalt as the colorant. It should have been
copper.
Marcia
Janet Moe / Paul Bailey wrote:
> I made a test batch of the following recipe. It came out purple with
> crawling. Very nice! A friend also made a test batch. It came out green
> as it should. Now I am wondering what I used? I was convinced I mixed it
> properly with the correct materials but obviously not. Any ideas? TIA
>
> Reitz Green - Cone 10 Reduction
>
> 70
> Nepheline Syenite
> 5 Calcium Carbonate
> 2 Gerstley Borate
> 15
> Petalite
> 8 EPK
> ____
> 100
>
> 1 Cobalt Carbonate
> 2 Rutile
>
> Janet, Denman Island, British Columbia
>
> ______________________________________________________________________________
> 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.
>
--
Tuscany in 2003
http://home.attbi.com/~m.selsor/Tuscany2003.html
John Hesselberth on fri 28 mar 03
On Friday, March 28, 2003, at 04:01 PM, Marcia Selsor wrote:
> I do think
> there was a similar error in Ron and John's book listing the recipe for
> carribean green and listing cobalt as the colorant
Hi Marcia,
Nope. Caribbean Sea Green uses cobalt carbonate and rutile. If you will
look at the photos on pages 100 and 101 you will see the dramatic
change that occurs when you go from 4.5% to 6% rutile.
Regards,
John
http://www.frogpondpottery.com
http://www.masteringglazes.com
Betty Fountain on fri 28 mar 03
Hi Janet,
The formula for Reitz Green in the Archives calls for only 1% of Rutile...
not 2 as in your formula. Hope this helps...
Regards from Connecticut,
Betty
Janet Moe / Paul Bailey on fri 28 mar 03
Marcia Selsor wrote:
> I believe Reitz Green has copper in it instead of Cobalt.
No, the recipe definitely calls for cobalt. As I said, my friends test
batch did come out green (she was hoping to get my purple crawl, I
wanted the green).
Donald G. Goldsobel on fri 28 mar 03
Reitz green has a tendency to be multi colored, but not purple. I think you
left out the rutile which creates the "rutile green" . When you do your next
test batch, vaary the thickness-that is when the plaid effect comes into
paly
Donald
>> ----- Original Message -----
From: "Janet Moe / Paul Bailey"
To:
Sent: Friday, March 28, 2003 10:27 AM
Subject: Glaze Puzzle
> I made a test batch of the following recipe. It came out purple with
> crawling. Very nice! A friend also made a test batch. It came out green
> as it should. Now I am wondering what I used? I was convinced I mixed it
> properly with the correct materials but obviously not. Any ideas? TIA
>
> Reitz Green - Cone 10 Reduction
>
> 70
> Nepheline Syenite
> 5 Calcium Carbonate
> 2 Gerstley Borate
> 15
> Petalite
> 8 EPK
> ____
> 100
>
> 1 Cobalt Carbonate
> 2 Rutile
>
> Janet, Denman Island, British Columbia
>
>
____________________________________________________________________________
__
> 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.
Gail Dapogny on sat 29 mar 03
Janet, I'm wondering what would happen if you had used copper oxide by
mistake. Could your purple be some offshoot of copper red? Someone more
knowledge might know about that. I do know that the glaze works with
either 1 or 2% rutile so it isn't that.
---Gail Dapogny in Ann Arbor
>I made a test batch of the following recipe. It came out purple with
>crawling. Very nice! A friend also made a test batch. It came out green
>as it should. Now I am wondering what I used? I was convinced I mixed it
>properly with the correct materials but obviously not. Any ideas? TIA
>
>Reitz Green - Cone 10 Reduction
>
>70
>Nepheline Syenite
> 5 Calcium Carbonate
> 2 Gerstley Borate
>15
>Petalite
> 8 EPK
>____
>100
>
> 1 Cobalt Carbonate
> 2 Rutile
>
>Janet, Denman Island, British Columbia
Elizabeth Priddy on sat 29 mar 03
If you liked it but didn't want the crawling, would manganese dioxide make it purple?
David Hendley wrote:Reitz Green is a well-known and well-tested glaze that does indeed
come out green where thick and dark gray to black where thin.
The green color does come from cobalt, which, in the presence
of titanium (rutile), in the right glaze formula, will be green rather
than blue.
A purple color from cobalt suggests that magnesium is present in
the glaze. The most common ingredient to induce crawling in
a glaze is magnesium carbonate. Therefore, I would bet that you
mistakenly used "magnesium carbonate", not "calcium carbonate"
when you mixed your glaze test.
David Hendley
Maydelle, Texas
david@farmpots.com
http://www.farmpots.com
----- Original Message -----
> I made a test batch of the following recipe. It came out purple with
> crawling. Very nice! A friend also made a test batch. It came out green
> as it should. Now I am wondering what I used? I was convinced I mixed it
> properly with the correct materials but obviously not. Any ideas? TIA
>
> Reitz Green - Cone 10 Reduction
>
> 70
> Nepheline Syenite
> 5 Calcium Carbonate
> 2 Gerstley Borate
> 15
> Petalite
> 8 EPK
> ____
> 100
>
> 1 Cobalt Carbonate
> 2 Rutile
>
______________________________________________________________________________
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.
---------------------------------
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Marcia Selsor on sat 29 mar 03
I will have to check with my co-op mates. They got a blue! I figured
someowhere it was transcribed worng. It happens.At least I have seen
copper and cobablt mixed up due to the wrong abbreviations by people.
My apologies and I will tell my co-op mates to check their notes again.
Thanks and I am glad you set me straight.
Marcia
John Hesselberth wrote:
>
> On Friday, March 28, 2003, at 04:01 PM, Marcia Selsor wrote:
>
>> I do think
>> there was a similar error in Ron and John's book listing the recipe for
>> carribean green and listing cobalt as the colorant
>
>
> Hi Marcia,
>
> Nope. Caribbean Sea Green uses cobalt carbonate and rutile. If you will
> look at the photos on pages 100 and 101 you will see the dramatic change
> that occurs when you go from 4.5% to 6% rutile.
>
> Regards,
>
> John
> http://www.frogpondpottery.com
> http://www.masteringglazes.com
>
>
--
Tuscany in 2003
http://home.attbi.com/~m.selsor/Tuscany2003.html
Fraser Forsythe on sat 29 mar 03
Hi.
Did you test with varying thickness. A glaze like this
will change a lot depending on thickness. First thing
that came to mind...
Fraser
--- Janet Moe / Paul Bailey
wrote: > I made a test batch of the following recipe.
It came
> out purple with
> crawling. Very nice! A friend also made a test
> batch. It came out green
> as it should. Now I am wondering what I used? I was
> convinced I mixed it
> properly with the correct materials but obviously
> not. Any ideas? TIA
>
> Reitz Green - Cone 10 Reduction
>
> 70
> Nepheline Syenite
> 5 Calcium Carbonate
> 2 Gerstley Borate
> 15
> Petalite
> 8 EPK
> ____
> 100
>
> 1 Cobalt Carbonate
> 2 Rutile
>
> Janet, Denman Island, British Columbia
>
>
______________________________________________________________________________
> 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.
______________________________________________________________________
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