wallace myers on sun 1 apr 01
Folks:
What would I do to the following glaze to correct crazing? I fire cone =
6 ox.
20.0 frit 3134
20.0 wollastonite
20.0 epk
20.0 flint
20.0 custer feldspar
Thanks.
Wallace
John Hesselberth on sun 1 apr 01
Hi Wallace,
A simple thing to try would be to add 10 % talc. This will still keep
alumina and silica in a good range and will add enough magnesium to lower
the glaze expansion noticeably. Do a line blend of the original and the
glaze with 10% talc and see where/if the crazing goes away.
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.
>
> What would I do to the following glaze to correct crazing? I fire cone 6 ox.
>
> 20.0 frit 3134
> 20.0 wollastonite
> 20.0 epk
> 20.0 flint
> 20.0 custer feldspar
>
> Thanks.
> Wallace
David Hewitt on mon 2 apr 01
My calculation of the coefficient of expansion for this glaze is 4.49 x
10-6/oC English & Turner.
The glaze that I use (clear shiny transparent) for cone 6 oxidation on
porcelain has a coefficient of 2.67. This does not craze.
As someone else has suggested, it might be the clay body that you are
using. A white stoneware or buff stoneware is less likely to craze than
a porcelain.
It would be interesting to know, therefore, what type of clay you are
using?
To bring the coefficient down to the figure of my glaze requires some
significant changes.
If you are interested the recipe is as follows:-
Wollastonite 82
China Clay 175
Dolomite 39
Potash Feldspar 39
Zinc oxide 13
Lithium carbonate 12
Flint/Quartz 256
BPS Low Exp. frit 384
___
1000
K2O 0.03 Al2O3 0.51 SiO2 4.02
Na2O 0.09 B2O3 0.40
CaO 0.67 Fe2O3 0.00
MgO 0.09
Li2O 0.06
ZnO 0.06
David
In message , wallace myers writes
>Folks:
>
>What would I do to the following glaze to correct crazing? I fire cone =
>6 ox.
>
>20.0 frit 3134
>20.0 wollastonite
>20.0 epk
>20.0 flint
>20.0 custer feldspar
>
>Thanks.
>Wallace
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP18 3DQ, UK. Tel:- +44 (0) 1633 420647
FAX:- +44 (0) 870 1617274
Web site http://www.dhpot.demon.co.uk
will edwards on mon 2 apr 01
Hello,
Wallace/other interested parties?? you didn't mention what clay you are u=
sing.
The glaze below (20x5)is usually a good one for many people and clays the=
y
use. I have seen some issues with some earthenware clays crazing using th=
e
formula as it stands. I believe Tony wrote this one to be a starting poin=
t for
people who would like to see how to make a stable glaze using a simple/gr=
eat
base.
Go to Insights home page on the web (Digitalfire)and see how he has made =
some
alterations there for an ultra clear. Till then I am sending you one I wr=
ote
and yes it was lab tested using many methods. Extractable boron was less =
than
a trace. Colorants I used in the lab tests are available through my book =
if
and when I get it finished. I have multiple recipes using colorant oxides=
with
this base. Try adding 2% Cobalt Oxide and 5% Rutile. Nice blue. This base=
is
only one of many I have ready to go...
The below formulation was worked out using MATRIX beta soon to be release=
d.
Lab resources used complies with USFDA/FSIS and was tested using ASTM met=
hods
for water standards. They are multiple ways for testing for oxide levels =
other
than water standards. (Many metals do not even have standards set for wat=
er
yet that are regulated). I need to throw that in there before I stir the
cauldron of overly reactive people. Avg. time elasped studies with acids=
and
other methods can be used to learn the extraction rates for specific
needs/materials. (No need to get into chromotography) The water standards=
are
the highest I can think of that will easily let you know what is readily
available via contact over a period of time with acids with or without
regulated materials. The results are the quickest determining method for =
the
worst possible scenario. (A safe approach to understanding health and haz=
ards
in glaze formulating) A vinegar soak has been used to eye-ball a bad glaz=
e but
it is not fool proof. According to some experts it is said to be the firs=
t
method for determining a truly bad glaze. Others use lemon slices and ora=
nge
slices! =
However I am off on a tangent that isn't about crazing exactly. Talk to T=
ony
Hanson or see his web site and go from there or till you get your fix you=
might try my glaze base below. It may not craze on your clay body or it m=
ay? I
would need to know which clay it is and if I have the analysis for it. Th=
e
Edward's 1234 Glossy is a forgiving glossy base however, since it works w=
ell
over several ranges of heat and ^6 being the one it was best written for.=
I
would stick with a clay that cures between ^3 and ^8 for this glaze as an=
average determiner for how to kick start the learning curve. I personally=
use
it on my ^10 B-MIX but thats me. (I have also talked to the technicians a=
t
Laguna about all this) And I haven't had any delayed crazing issues but I=
state clearly that is not why I spoke with them. Maybe someone else would=
challenge that by testing it more and letting me know? This only proves t=
hat
since we have a zillion choices to pull from we will only know the answer=
by
physical testing and presenting the facts as they come out.
Edward's 1.2.3.4.. GLOSSY GLAZE BASE =A9 Ox. 2194deg.F. Cone 6
-------------------------------------------------------------------------=
-
Formula Analysis Recipe
-------------------------------------------------------------------------=
-
KNO 0.2237 4.09% Ferro 3134 40.00
CaO 0.7713 12.75% EPK Kaolin 30.00
Al2O3 0.3745 11.25% Silica 20.00
B2O3 0.4477 9.18% Wollastonite 10.00
SiO2 3.2038 57.41% =
TiO2 0.0047 0.17% =
Na2O 0.2237 4.09% =
Al:Si 8.5549 =
Expan. 9.1799 =
ST 3.5223 =
William Edwards
Alchemy 101 =
Folks
What would I do to the following glaze to correct crazing? I fire cone 6 =
ox.
20.0 frit 3134
20.0 wollastonite
20.0 epk
20.0 flint
20.0 custer feldspar
Thanks.
Wallace
____________________________________________________________________
Get free email and a permanent address at http://www.netaddress.com/?N=3D=
1
Lewis Crittenden on mon 2 apr 01
Will Edwards... In your reply to this post, you suggested the
Edward's 1,2,3,4 glaze and then listed it. The original post used
the Hanson 5X20. According to my calculations, the Hanson glaze has an
expansion of 7.14 and this glaze crazed. Your glaze suggestion shows an
expansion of 9.17. I have a problem understanding how a substantial increase in
expansion will decrease crazing. Could you please explain. My copy of Magic of
Fire II states that one reduces expansion to reduce crazing. This is found on
page 66.
--- Lewis Crittenden
--- theoblue44@earthlink.net
--- EarthLink: It's your Internet.
Dan Hill on tue 3 apr 01
Wallace
Using Insight calc. software I have lowered the expansion of your glaze from
450 to 400. That should help the crazing problem. Basically what I did was
raise the boron,(flux), which allowed me to add a bit more silica and
alumina. All of these materials have a low expansion which helps to lower
the overall expansion of the glaze.
The ratio of silica to alumina was keep the same which should result in the
fired glaze being the same as the original.
Dan Hill
Wilno Ontario Canada
-----Original Message-----
From: wallace myers
To: CLAYART@LSV.CERAMICS.ORG
Date: 1 kwietnia 2001 15:05
Subject: need a fix for crazing
Folks:
What would I do to the following glaze to correct crazing? I fire cone 6
ox.
20.0 frit 3134
20.0 wollastonite
20.0 epk
20.0 flint
20.0 custer feldspar
Thanks.
Wallace
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