Sellan, Mark on tue 17 jul 01
I'm looking for recommendations about where to get or how to make a food
safe Turquoise glaze for use over porcelain. I'm a relatively new student
to clay and don't yet know much about mixing glazes.
Thanks much,
-mark
Dale Neese on tue 17 jul 01
Here is a Turquoise cone 10 that has been around awhile.
WEISER TURQUOISE
CUSTER SPAR 63
DOLOMITE 24
BALL CLAY 9
FLINT 4
COLBALT CARB .5
CHROME OX. 1.5
add your favorite suspension agent because this glaze will tend settle like
concrete if not used regularly. Nice on porcelain as well as stoneware.
DALE TEX
Jeremy McLeod on tue 17 jul 01
"Sellan, Mark" wrote:
> I'm looking for recommendations about where to get or how to make a food
> safe Turquoise glaze for use over porcelain.
Don't have a formula/recipe to share, but just want to point in the direction
of Oribe Turquoise as a fine option. I'm in the middle of a "green period"
and this glaze (in the ^10 public studio in which I study/work) is richly
rewarding.
Jeremy McLeod
John Weber on wed 18 jul 01
OK, I am trying hard to learn how to use Insight so I put this glaze into it
and then compared the results with the Limits published by Green & Cooper.
This glaze calculates out to contain Si 2.40 and Al203 .37 . The limits for
Cone 10 are Si 3.50 to 6.40 and for Al203 .45 to .825. Showing the glaze to
be way too low on both Si and Al203. However, when I look at Cone 6 limits
is shows the range to be Si 2.40 to 4.70 and Al203 from .275 to .65. If I
believe these limits it would tell me this is not a Cone 10 glaze but a Cone
6 Glaze. Do any of the 'real' glaze guru's have a thought on this problem?
> -----Original Message-----
> From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG]On
> Behalf Of Dale Neese
> Sent: Tuesday, July 17, 2001 3:40 PM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: Looking for Turquoise High Fire Glaze
>
>
> Here is a Turquoise cone 10 that has been around awhile.
>
> WEISER TURQUOISE
>
> CUSTER SPAR 63
> DOLOMITE 24
> BALL CLAY 9
> FLINT 4
> COLBALT CARB .5
> CHROME OX. 1.5
> add your favorite suspension agent because this glaze will tend
> settle like
> concrete if not used regularly. Nice on porcelain as well as stoneware.
>
> DALE TEX
>
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>
John Hesselberth on wed 18 jul 01
on 7/18/01 9:53 AM, John Weber at jodopottery@MEDIAONE.NET wrote:
> OK, I am trying hard to learn how to use Insight so I put this glaze into it
> and then compared the results with the Limits published by Green & Cooper.
> This glaze calculates out to contain Si 2.40 and Al203 .37 . The limits for
> Cone 10 are Si 3.50 to 6.40 and for Al203 .45 to .825. Showing the glaze to
> be way too low on both Si and Al203. However, when I look at Cone 6 limits
> is shows the range to be Si 2.40 to 4.70 and Al203 from .275 to .65. If I
> believe these limits it would tell me this is not a Cone 10 glaze but a Cone
> 6 Glaze. Do any of the 'real' glaze guru's have a thought on this problem?
Hi John,
The question you ask is not a straight-forward one to answer, but I'll talk
around it for a while. First limits are only guidelines. Your chances of
making a good glaze are better within limits, but there are good glazes
outside limits too. Limits were not constructed from heavy-duty scientific
experiments. The authors generally took glazes they were familiar with that
made "good glass", then looked at the unity formulas and extracted what they
saw as common threads. They probably also drew on the published literature
and on their own experience.
You can't tell whether this is a cone 6 or cone 10 glaze without also
looking at the combination of fluxes + boron; however it is on the low side
of silica even for a cone 6 glaze. My own recommendations are 2.5 or above,
preferably above 3.0 for durable cone 6 glazes. Tell us the rest of the
unity formula if you want us to comment further. And don't get discouraged.
After you've looked at a few glazes you will be able to tell a lot about the
glaze by looking at its unity formula.
Regards,
John
Web site: http://www.frogpondpottery.com Email: john@frogpondpottery.com
"The life so short, the craft so long to learn." Chaucer's translation of
Hippocrates, 5th cent. B.C.
John Baymore on thu 19 jul 01
Limits were not constructed from heavy-duty scientific
experiments. The authors generally took glazes they were familiar with
that
made "good glass", then looked at the unity formulas and extracted what
they
saw as common threads.
Great comments by John H. on this subject.
To add a thought to the above............
Most potters definition of a "good glass" (as mentioned above) is based
SOLELY on a visual inspection of the samples .... not on any scientific
testing. Kind'a a macro view instead of a micro view. "If it looks like=
glass, smells like glass, and tastes like glass...... it's glass ." F=
ew
potters submit glazes for leach testing, few do any kinds of
hardness/abasion testing, few even do tests for actual clay/body fit. =
Mostly we just look at it.... if we like it....we use it.
As we are finding out as we look at many of the "old reliable" high fire
glaze formulas floating around....... many are not really all that "good=
".
Back in the 60's and early 70's many of us potters used pretty high free
silica clay bodies..... lots of clays....not much flux. So many of these=
high fire glazes that were deficient in silica and alumina "robbed" some =
of
what they "wanted" from the clay body interface..... which helped them ou=
t
a tad. Now most of us are using pretty well developed clay bodies....so
the silica starved glazes don't fare quite as well in that regard anymore=
.
Best,
..............................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752 (s)
800-900-1110 (s)
JohnBaymore.com
JBaymore@compuserve.com
John.Baymore@GSD-CO.com
"Earth, Water, and Fire Noborigama Woodfiring Workshop August 17-26,
2001"
Ian Currie on thu 19 jul 01
Hi John
It can be really hard to get a good turquoise while trying to stay "within
the limits". The grid method I use does not tell what will be stable.
Though the stable ones tend to be towards the high alumina/high silica
corner as long as they are properly matured.
I put that first because in many cases you find a simple trade-off where the
turquoise (from copper) turns green as one increases alumina. This is seen
clearly in one of my grid tiles with the turquoise changing to copper green
as we move from the bottom of the grid to the top (high alumina).
High temperature brings more problems. The turquoise gets less intense
(with the same glaze) as you fire higher. This may simply be the copper
disappearing from the glaze, which is what copper does gradually at high
temperarures.
Low temperature turquoise with copper is easy, using lots of frit and not
too much clay in the glaze, but my friends Ron and John will look askance at
the low silica and alumina and worry about it's stability... which we all
should do if we think we might put these inside pots to be used with wine,
vinegar etc. I use a stable liner glaze inside.
I have not tried the recipe listed below in your post, but the colour comes
from cobalt and chrome. In this base glaze I suspect the chrome is going to
opacify the glaze which may be what you want, but may also deaden the glaze
quality???
A good possibility for a high temperature turquoise is from barium. Blue
can be obtained with copper in high alumina barium glazes, but they usually
need to be low in silica... so we are still talking of a glaze that needs to
be tested before mass producing your glazed-inside-with-turquoise wine
goblets! We all know by now about the problems that copper can bring to
glaze stability (a visit to John Hesselberth's studio last year was an
eye-opener for me!), and with lots of poisonous barium in the glaze we need
to know the pot will be safe to use. Once again, I use a stable liner
glaze. Incidentally, the result will most likely not be the same with
strontium, in spite of what is said.... but strontium does its own
interesting things with copper.
Some grids I've done show that the alumina/silica balance needs to be fairly
precise to get the blue. It is an ink-y blue that occurs where thick on
just a few glazes on the grid of a set with high barium and copper added...
up towards the A corner (high alumina). One of the advantages of the grid
method is that it gives a spread of alumina/silica values. Where the colour
is sensitive to alumina/silica balance, this gives maximum chance of finding
what you want, or at least seeing the trade-offs. These high alumina barium
glazes usually have a beautiful matt surface.
A good recipe to start might be Bev's Cu2 listed on page 81 of my latest
book, with a photo of one of Hank Murrow's pots. I will Cc Hank and Bev to
see if I can post the recipe on Clayart for you.
In the photo in my book you will see that the glaze is transparent where
thin. This means that if you want the blue to be vibrant it should be on a
white clay.
If you would like to know more about my grid method you can read about it at
my website:
http://ian.currie.to/
The book can be purchased by credit card at that website. It is called
"Revealing Glazes - Using the Grid Method"
Hope this is some help.... but high-temperature-vibrant-stable-turquoise is
a big ask!
regards
Ian
http://ian.currie.to/
-----Original Message-----
From: John Weber
To: CLAYART@LSV.CERAMICS.ORG
Date: Thursday, 19 July 2001 12:42
Subject: Re: Looking for Turquoise High Fire Glaze
>OK, I am trying hard to learn how to use Insight so I put this glaze into
it
>and then compared the results with the Limits published by Green & Cooper.
>This glaze calculates out to contain Si 2.40 and Al203 .37 . The limits
for
>Cone 10 are Si 3.50 to 6.40 and for Al203 .45 to .825. Showing the glaze
to
>be way too low on both Si and Al203. However, when I look at Cone 6 limits
>is shows the range to be Si 2.40 to 4.70 and Al203 from .275 to .65. If I
>believe these limits it would tell me this is not a Cone 10 glaze but a
Cone
>6 Glaze. Do any of the 'real' glaze guru's have a thought on this problem?
>
>> -----Original Message-----
>> From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG]On
>> Behalf Of Dale Neese
>> Sent: Tuesday, July 17, 2001 3:40 PM
>> To: CLAYART@LSV.CERAMICS.ORG
>> Subject: Re: Looking for Turquoise High Fire Glaze
>>
>>
>> Here is a Turquoise cone 10 that has been around awhile.
>>
>> WEISER TURQUOISE
>>
>> CUSTER SPAR 63
>> DOLOMITE 24
>> BALL CLAY 9
>> FLINT 4
>> COLBALT CARB .5
>> CHROME OX. 1.5
>> add your favorite suspension agent because this glaze will tend
>> settle like
>> concrete if not used regularly. Nice on porcelain as well as stoneware.
>>
>> DALE TEX
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