Bjerkan on wed 2 dec 98
How can I get my crackle glaze to crackle more? Are there any tricks to =
working
with this type of glaze?TIA peggy
Bjerkan on thu 3 dec 98
How can I get my crackle glaze to crackle more? Are there any tricks to =
working
with this type of glaze?TIA peggy
David Hewitt on thu 3 dec 98
Any or all of the follwing will tend to produce more crazing:-
1) Fire higher to form more cristobalite in the body.
2) Fire for longer by soaking towards the top end of the firing -
creating more cristobalite.
3) Alter the glaze by lowering its coefficient of expansion; i.e.
substituting oxides with low expansion for those with high expansion.
4) Change the body to one of higher expansion
David
In message , Bjerkan writes
>----------------------------Original message----------------------------
>How can I get my crackle glaze to crackle more? Are there any tricks to =
>working
>with this type of glaze?TIA peggy
>
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP6 1DQ, UK. Tel:- +44 (0) 1633 420647
FAX:- +44 (0) 870 1617274
Own Web site http://www.dhpot.demon.co.uk
IMC Web site http://digitalfire.com/education/people/hewitt.htm
Mike Gordon on fri 4 dec 98
Peggy,
What kind of firing are you talking about? Crackle glaze comes at a lot
of different temps. and atmospheres. Mike
Craig Martell on sat 5 dec 98
David Hewitt wrote:
----------------------------Original message----------------------------
Any or all of the follwing will tend to produce more crazing:-
1) Fire higher to form more cristobalite in the body.
2) Fire for longer by soaking towards the top end of the firing -
creating more cristobalite.
3) Alter the glaze by lowering its coefficient of expansion; i.e.
substituting oxides with low expansion for those with high expansion.
4) Change the body to one of higher expansion
Hello David:
According to what I've learned over the years about clay and glazes and
expansion of either, suggestions 1 thru 3 will have the opposite effect in
regard to crazing.
If you raise the level of cristobalite in the claybody, you subject ware to
a double volume change which will tend to move a glaze more toward the range
of compression and not tension, which will cause crazing. High cristobalite
bodies are quite often the culprit in regard to shivering and not crazing.
If you want a glaze to craze more, you must raise it's coefficient of
expansion thereby creating a greater possibility for tension and crazing, or
crackle. Also, high expansion bodies with more spar than is necessary are
hard to fit glazes to and crazing is more of a problem. These high spar
bodies don't develop problems with cristobalite because it is taken into the
body glass, which is fused silica and has a lower expansion than crystalline
silica. ad nauseum!~!!
regards, Craig Martell in Oregon
Jim Brooks on sun 6 dec 98
you can make most glazes craze by lowering the silica. If you have a base
glaze you like.. test it with decreasing silica.. by maybe 5% less for each
test tile.. Some will not yield results that you may want.. but you may also
be very surprised to find you have the making for the crazedglaze at
hand.......
David Hewitt on sun 6 dec 98
I wish to thank Craig Martell and Tony Hansen for pointing out that my
original answer in fact listed ways of reducing crazing, not increasing
it. I have no rational explanation for giving this totally wrong answer
so I won't try. To increase crazing, therefore, please reverse these
arguments as follows:-
1) Fire a low as possible - compatible with other requirements - to
limit cristobalite formation. (Over firing of non cristobalite bodies
may also cause crazing)
2) Limit soaking as far as posible - compatible with other requirements
- to limit cristobalite formation.
3) Alter the glaze by increasing its coefficent of expansion; 1.e.
substituting oxides with high expansion for those with low expansion.
4) Change the clay body to one with a lower coefficient of expansion.
My apologies for possibly misleading anyone.
David
In message , Craig Martell writes
>----------------------------Original message----------------------------
>David Hewitt wrote:
>
>----------------------------Original message----------------------------
>Any or all of the follwing will tend to produce more crazing:-
>1) Fire higher to form more cristobalite in the body.
>2) Fire for longer by soaking towards the top end of the firing -
>creating more cristobalite.
>3) Alter the glaze by lowering its coefficient of expansion; i.e.
>substituting oxides with low expansion for those with high expansion.
>4) Change the body to one of higher expansion
>
>
>Hello David:
>
>According to what I've learned over the years about clay and glazes and
>expansion of either, suggestions 1 thru 3 will have the opposite effect in
>regard to crazing.
>
>If you raise the level of cristobalite in the claybody, you subject ware to
>a double volume change which will tend to move a glaze more toward the range
>of compression and not tension, which will cause crazing. High cristobalite
>bodies are quite often the culprit in regard to shivering and not crazing.
>
>If you want a glaze to craze more, you must raise it's coefficient of
>expansion thereby creating a greater possibility for tension and crazing, or
>crackle. Also, high expansion bodies with more spar than is necessary are
>hard to fit glazes to and crazing is more of a problem. These high spar
>bodies don't develop problems with cristobalite because it is taken into the
>body glass, which is fused silica and has a lower expansion than crystalline
>silica. ad nauseum!~!!
>
>regards, Craig Martell in Oregon
>
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP6 1DQ, UK. Tel:- +44 (0) 1633 420647
FAX:- +44 (0) 870 1617274
Own Web site http://www.dhpot.demon.co.uk
IMC Web site http://digitalfire.com/education/people/hewitt.htm
Maggie Woodhead on fri 19 feb 99
Kia Ora!
It was a hot windy day so I worked on 'Insight ' which had to
be reinstalled
and it seems to be working well now.
These are the two glazes I put on and compared. The 'Shino' is
the first one I tried with the small crackle. The other 'Crackle' is my
workout on the programme.
One question I have to ask, why does the Shino which has only 4.47
Si/Al appear to be quite shiny when in Ron Roy's letter of 20/03/98 to
Clayart he says under 5 should be matte?
SHINO
NEPHELINE SYENITE--80
BALL CLAY (AUS)-------20
SILICA-------------------------5
SALT---------------------------5
CaO---.06
Mg0---.02
K20---.22
Na20---.7
Al203-.1.32
Si02--5.92 Si:Al 4.47 Exp 8.14
CRACKLE
FELDSPAR (UK SODA)-----------58
TALC-------------------------------------12
WOLLASTONITE---------------------15
BALL CLAY (AUS)-------------------5
SILICA------------------------------------10
Ca0-----.48
Mg0-----.27
K20-----.05
Na20---.2
Al203--.35
Si20----2.83 Si:Al--8.11 Exp---7.24
The other shino I have tried is the Len Castle one Potash feldspar 85
and Talc15.
Looks about the same as the first one, same size crackle, same orange
underneath.
Would also like to get it a bit whiter, these are a bit grey in
colour the clay has some Fe I think.
----Best Wishes Maggie----
maggie@clear.net.nz
David Hewitt on sun 21 feb 99
In message , Maggie Woodhead writes
>----------------------------Original message----------------------------
>Kia Ora!
>
> One question I have to ask, why does the Shino which has only 4.47
>Si/Al appear to be quite shiny when in Ron Roy's letter of 20/03/98 to
>Clayart he says under 5 should be matte?
I would think it is because there is a vast difference in the Basic
oxides in the two recipes.
The first is almost entirely alkali (K2O .22 and Na2O .7) and so has
greater fluxing power than the second. The second is strongly alkaline
earth ( CaO .48 MgO .27). these respectively give alkali/alkaline earth
ratios of 1/.09 and 1/3
David
>
>SHINO
>NEPHELINE SYENITE--80
>BALL CLAY (AUS)-------20
>SILICA-------------------------5
>SALT---------------------------5
>
>CaO---.06
>Mg0---.02
>K20---.22
>Na20---.7
>Al203-.1.32
>Si02--5.92 Si:Al 4.47 Exp 8.14
>
>CRACKLE
>FELDSPAR (UK SODA)-----------58
>TALC-------------------------------------12
>WOLLASTONITE---------------------15
>BALL CLAY (AUS)-------------------5
>SILICA------------------------------------10
>
>Ca0-----.48
>Mg0-----.27
>K20-----.05
>Na20---.2
>Al203--.35
>Si20----2.83 Si:Al--8.11 Exp---7.24
>
>----Best Wishes Maggie----
> maggie@clear.net.nz
>
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP6 1DQ, UK. Tel:- +44 (0) 1633 420647
FAX:- +44 (0) 870 1617274
Own Web site http://www.dhpot.demon.co.uk
IMC Web site http://digitalfire.com/education/people/hewitt.htm
Ron Roy on sun 21 feb 99
Hi Maggie,
It's kinda scary to me to have something I said about a year ago pop up
like this - you have been doing your homework - you get a star!
There is an excellent article in the December 92 Issue of The Studio Potter
by Jim Robinson (Volume 21 #1) on Shino glazes.
First of all the ratio thing - used for guessing the surface of a glaze is
not fool proof. Much depends on the balance and kinds of oxides in a glaze.
Shino glazes are certainly unbalanced glazes - high in both KNaO and
Alumina. You have to read the article to get more info on that aspect.
The other part of what happens to the surface of many Shino's - even though
they are high in Alumina and low in Silica - there is usually considerable
soluble sodium present - salt, soda ash, and I think probably sodium
bicarbonate as well - these salts migrate to the surface as the glaze dries
and helps to melt the surface more. We are in fact looking at two glazes -
the one on the surface has more sodium - it's why it is so hard to stop
Shino's from crazing on many bodies.
Hope you can get to see a copy of the Studio Potters - quality stuff. I
have been working with Peter Sohngen on some experiments - clay body and
cristobalite stuff - and it will be published there as well.
I am sure I have seen their URL here but - would someone please post it for
those wanting to check it out.
RR
> One question I have to ask, why does the Shino which has only 4.47
>Si/Al appear to be quite shiny when in Ron Roy's letter of 20/03/98 to
>Clayart he says under 5 should be matte?
>
>SHINO
>NEPHELINE SYENITE--80
>BALL CLAY (AUS)-------20
>SILICA-------------------------5
>SALT---------------------------5
>
>CaO---.06
>Mg0---.02
>K20---.22
>Na20---.7
>Al203-.1.32
>Si02--5.92 Si:Al 4.47 Exp 8.14
> maggie@clear.net.nz
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
Chris Clyburn on sun 9 nov 03
I have a quick question. I have focused for a while on mostly sculptural
pieces and am only now really getting into wanting to do functional ware. I
am making a teaset for my in-laws for christmas and They have requested a
green glaze. All the green glazes I can find in a shade they like are
crackle glazes. The crackle is just spiderweb like and does not expose the
body that I can tell. My professor retired last spring and the guy they
replaced him with has to teach from books (almost no actual experince with
clay, so I can't ask him and trust the answer). So, could somebody tell me
if crackle glazes can be used in a teaset? My experience tells me no, but I
have no cone 9-10 oxidation greens I can use otherwise and no time to
formulate new ones. Any help would be greatly appreciated.
Chris Clyburn
Susan Setley on sun 9 nov 03
In a message dated 11/9/03 5:05:01 PM, earthfire_studios@COX.NET writes:
<< My experience tells me no, but I
have no cone 9-10 oxidation greens I can use otherwise and no time to
formulate new ones. Any help would be greatly appreciated. >>
The Reitz green glaze we use works well on three different clay bodies in our
studio. The green is a kelly green that breaks out into black. Personally I
like it in small doses -- we often combine it with St. John's Black.
If you want the recipe let me know. It is well proven to do well at ^10 on
two different stoneware bodies and one porcelainous white clay.
Tony Hansen on mon 10 nov 03
How about adding a chrome/cobalt or
copper/cobalt combination to an existing
transparent glaze? Add a little rutile
or titanium for some character.
Rutile and cobalt can crystallize to form
green glazes also, but I think you need
higher alumina and lower silica for this
to work best.
-------8<--------
On Mon, 10 Nov 2003 10:19:53 -0500, Tony Hansen wrote:
>Why not take an existing glossy glaze that you
>use and remove all the colorants and insert a green
>stain? Call Mason Stains on the phone, they are very
>helpful.
There are three problems with that solution. First I don\'t have any cash to
order supplies with. Second it might take too long to get here and third I
am under the impression (maybe erroneously) that mason stains in a glaze
give a flat paint-like appearance and I would prefer something with some
visual texture. I appreciate the suggestion...but under current
circumstances I don\'t think it\'s a viable solution.
Chris Clyburn
______________________________________________________________________________
Send postings to clayart@lsv.ceramics.org
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-------
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Tony Hansen on mon 10 nov 03
Why not take an existing glossy glaze that you
use and remove all the colorants and insert a green
stain? Call Mason Stains on the phone, they are very
helpful.
-------8<--------
I have a quick question. I have focused for a while on mostly sculptural
pieces and am only now really getting into wanting to do functional ware. I
am making a teaset for my in-laws for christmas and They have requested a
green glaze. All the green glazes I can find in a shade they like are
crackle glazes. The crackle is just spiderweb like and does not expose the
body that I can tell. My professor retired last spring and the guy they
replaced him with has to teach from books (almost no actual experince with
clay, so I can\'t ask him and trust the answer). So, could somebody tell me
if crackle glazes can be used in a teaset? My experience tells me no, but I
have no cone 9-10 oxidation greens I can use otherwise and no time to
formulate new ones. Any help would be greatly appreciated.
Chris Clyburn
-------
Tony Hansen, http://digitalfire.com
Personal Contact Page: http://digitalfire.com/services/contact.php
Calculation/Database Software for Ceramic Industry
Chris Clyburn on mon 10 nov 03
On Mon, 10 Nov 2003 10:19:53 -0500, Tony Hansen wrote:
>Why not take an existing glossy glaze that you
>use and remove all the colorants and insert a green
>stain? Call Mason Stains on the phone, they are very
>helpful.
There are three problems with that solution. First I don't have any cash to
order supplies with. Second it might take too long to get here and third I
am under the impression (maybe erroneously) that mason stains in a glaze
give a flat paint-like appearance and I would prefer something with some
visual texture. I appreciate the suggestion...but under current
circumstances I don't think it's a viable solution.
Chris Clyburn
Chris Clyburn on tue 11 nov 03
On Tue, 11 Nov 2003 15:07:15 -0800, Hank Murrow wrote:
>Dear All;
>
>The Reitz Green I use is a Cobalt/Rutile green, and was a shino until
>someone tried the Co/Ru combo. Clear where very thin, charcoal where
>medium, and mossy green as it gets thicker. Sometimes flashes to a very
>intense Prussian Blue on edges. See 055, 056, 090, b016, & b022 on the
>'current pots' page at my site.
Are you firing oxidation or reduction to get those colors? Beautiful pots by
the way.
Chris Clyburn
Chris Clyburn on tue 11 nov 03
On Tue, 11 Nov 2003 16:56:58 -0500, Ron Roy wrote:
>The Reitz green is an Oribe type glaze I think - 5 or 5 % copper - right.
>
>Anyway they are all subject to attack by acidic food - you can probably
>taste the copper in orange juice after only a few minutes.
>
>Before putting on food bearing surfaces - give it the lemon test.
>
I looked online and through some of my books, but I cannot for the life of
me find out exactly what an Oribe glaze is. I found plenty of nice photos
but no descriptions. What is the firing range and atmosphere? Is it just the
a standard glaze or is it a regional style?
Chris Clyburn
Currently studying (well taking a break from) for an 8 page 600 location
map test tommorrow from a study guide chalk full of errors. You have to love
professors who like to give large tests and then complicate matters by
making faulty study guides where half the info that is wrong is not located
_anywhere_ in the course material for corrections...grrrrrrrrr
Ron Roy on tue 11 nov 03
The Reitz green is an Oribe type glaze I think - 5 or 5 % copper - right.
Anyway they are all subject to attack by acidic food - you can probably
taste the copper in orange juice after only a few minutes.
Before putting on food bearing surfaces - give it the lemon test.
RR
>The Reitz green glaze we use works well on three different clay bodies in our
>studio. The green is a kelly green that breaks out into black. Personally I
>like it in small doses -- we often combine it with St. John's Black.
>
>If you want the recipe let me know. It is well proven to do well at ^10 on
>two different stoneware bodies and one porcelainous white clay.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Hank Murrow on tue 11 nov 03
Dear All;
The Reitz Green I use is a Cobalt/Rutile green, and was a shino until
someone tried the Co/Ru combo. Clear where very thin, charcoal where
medium, and mossy green as it gets thicker. Sometimes flashes to a very
intense Prussian Blue on edges. See 055, 056, 090, b016, & b022 on the
'current pots' page at my site.
Cheers Group, Hank
www.murrow.biz/hank
On Nov 11, 2003, at 1:56 PM, Ron Roy wrote:
> The Reitz green is an Oribe type glaze I think - 5 or 5 % copper -
> right.
>
> Anyway they are all subject to attack by acidic food - you can probably
> taste the copper in orange juice after only a few minutes.
>
> Before putting on food bearing surfaces - give it the lemon test.
>
> RR
>
>
>> The Reitz green glaze we use works well on three different clay
>> bodies in our
>> studio. The green is a kelly green that breaks out into black.
>> Personally I
>> like it in small doses -- we often combine it with St. John's Black.
>>
>> If you want the recipe let me know. It is well proven to do well at
>> ^10 on
>> two different stoneware bodies and one porcelainous white clay.
Chris Clyburn on wed 12 nov 03
On Wed, 12 Nov 2003 04:04:15 -0800, Gail Dapogny wrote:
>Following is the recipe for Reitz Green:
>Cone 9-10 Reduction
>Neph Sy 69.31
>Calcium Carbonate 5.94
>Gerstley Borate 1.98
>Petalite 14.85
>Kaolin 7.92
>Cobalt Carbonate 1.00
>Rutile 1.00
>
>I have had the same experience as Hank -- getting blue wherever it is
>thin or where something else touches it or overlaps with it. I don't
>care for the blue showing up, so don't find myself using it a lot. I'd
>love to be able to get rid of the blue. Any ideas, or any glazes that
>look similar but don't have cobalt in them?
>---Gail Dapogny
>
Thanks for all the info, Hopefully I can test all the ideas I was given by
next Saturday, with any luck, my in-laws will have their green tea set fro
Christmas and I can have some peace :-)
BTW, I bombed my map test....weeks of studying and I go blank when it comes
to the actual test...sigh....looks Like it's another two weeks of studying
this monster and then attempt to pass the remake. Oh well, thats what I get
for trying to get a degree I guess.
Chris Clyburn
Currrently anxious to be done with school so I can start potting full time.
Senior burn out is hitting hard :-)
Hank Murrow on wed 12 nov 03
Dear Chris;
The pots are fired to C/10 in either reduction or oxidation.........and
on pretty white clays.
Hank in Eugene
On Nov 11, 2003, at 5:36 PM, Chris Clyburn wrote:
> On Tue, 11 Nov 2003 15:07:15 -0800, Hank Murrow
> wrote:
>> The Reitz Green I use is a Cobalt/Rutile green, and was a shino until
>> someone tried the Co/Ru combo. Clear where very thin, charcoal where
>> medium, and mossy green as it gets thicker. Sometimes flashes to a
>> very
>> intense Prussian Blue on edges. See 055, 056, 090, b016, & b022 on the
>> 'current pots' page at my site.
>
>
> Are you firing oxidation or reduction to get those colors? Beautiful
> pots by
> the way.
>
> Chris Clyburn
Gail Dapogny on wed 12 nov 03
Following is the recipe for Reitz Green:
Cone 9-10 Reduction
Neph Sy 69.31
Calcium Carbonate 5.94
Gerstley Borate 1.98
Petalite 14.85
Kaolin 7.92
Cobalt Carbonate 1.00
Rutile 1.00
I have had the same experience as Hank -- getting blue wherever it is
thin or where something else touches it or overlaps with it. I don't
care for the blue showing up, so don't find myself using it a lot. I'd
love to be able to get rid of the blue. Any ideas, or any glazes that
look similar but don't have cobalt in them?
---Gail Dapogny
On Nov 11, 2003, at 3:07 PM, Hank Murrow wrote:
> Dear All;
>
> The Reitz Green I use is a Cobalt/Rutile green, and was a shino until
> someone tried the Co/Ru combo. Clear where very thin, charcoal where
> medium, and mossy green as it gets thicker. Sometimes flashes to a very
> intense Prussian Blue on edges. See 055, 056, 090, b016, & b022 on the
> 'current pots' page at my site.
>
> Cheers Group, Hank
> www.murrow.biz/hank
>
> On Nov 11, 2003, at 1:56 PM, Ron Roy wrote:
>
>> The Reitz green is an Oribe type glaze I think - 5 or 5 % copper -
>> right.
>>
>> Anyway they are all subject to attack by acidic food - you can
>> probably
>> taste the copper in orange juice after only a few minutes.
>>
>> Before putting on food bearing surfaces - give it the lemon test.
>>
>> RR
>>
>>
>>> The Reitz green glaze we use works well on three different clay
>>> bodies in our
>>> studio. The green is a kelly green that breaks out into black.
>>> Personally I
>>> like it in small doses -- we often combine it with St. John's Black.
>>>
>>> If you want the recipe let me know. It is well proven to do well at
>>> ^10 on
>>> two different stoneware bodies and one porcelainous white clay.
>
> _______________________________________________________________________
> _______
> 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 gdapogny@umich.edu
1154 Olden Road
Ann Arbor, Michigan 48103
http://www.silverhawk.com/ex99/dapogny (single historical photo - no
longer
John Britt on mon 18 oct 04
Yes,
Reduction or oxidation at cone 10.
John
www.johnbrittpottery.com
Kate Atkinson on mon 18 oct 04
HELP. I have a student who is desperately trying to produce a good crackle
glaze at 1260c Oxidation and every recipe I have given her has failed, lots
of lovely crawling but no good crackles! Does anybody out there have any
white crackle glazes that are reliable at 1260c
Thanks, Kate
_________________________________________________________________
Express yourself with cool new emoticons http://www.msn.co.uk/specials/myemo
John Britt on mon 18 oct 04
Here is a glaze from my book,
CHINESE CRACKLE
Custer Feldspar 83.00
Silica 8.00
Whiting 9.00
Zircopax 10.00
Hope it helps,
John Britt
www.johnbrittpottery.com
Mike Gordon on mon 18 oct 04
John,
Is this cone 10, reduction? Mike Gordon
On Oct 18, 2004, at 4:33 PM, John Britt wrote:
> Here is a glaze from my book,
>
>
> CHINESE CRACKLE
>
>
> Custer Feldspar 83.00
> Silica 8.00
> Whiting 9.00
>
>
> Zircopax 10.00
>
> Hope it helps,
>
> John Britt
> www.johnbrittpottery.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.
>
Ivor and Olive Lewis on tue 19 oct 04
Dear Kate Atkinson,
I know of only one answer to this and it relates to questions about
the clay that is being used and the recipes that are applied.
We know little about our clay and we use recipes based on their
aesthetic characteristics. The second is most important since it means
we ignore other important pieces of information which are contained in
a glaze recipe that are never defined or described.
So getting a good match, which your student is failing to do, is more
"miss" than "hit" in a hit or miss situation. Long shot gambling !!!
My suggestion is to send your student back to first principles and do
some 6*6 tiles. She (of He) needs to qualify the optical properties
(Opaque<>Translucent<>Transparent), suggest the best ingredients for
the chosen temperature then do the weighting, mixing. Always test on
the range of clays available in your studio. The first firing should
give a few potential mixtures.
If you would like more information contact me "Off List" as there are
ways of increasing the number of "Winners" when doing this sort of
research that are not given in text books.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
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