veenaraghavan on fri 17 aug 12
Hi folks.=3D20
Can anyone help a friend of mine who acquired lots of cone 06 clay to make =
i=3D
t withstand raku firing. Would playground sand work he needs to keep down =
e=3D
xpenses down! Can you suggest percentages. He will be adding whatever it i=
s=3D
to moist clay.Thanks in advance. Happy rest of summer all.=3D20
Veena
Sent from my iPhone=3D
Gerholdclay on sat 18 aug 12
Recommend adding kyanite 30-35 mesh at 10 percent and 100 mesh grog to a ma=
x=3D
of 10 percent. This assumes clay is not already frogged in which case jus=
t=3D
use the Kyanite. Of course the normal caveats about testing apply.
Paul
Sent from my iPad
On Aug 17, 2012, at 3:57 PM, veenaraghavan wrote:
> Hi folks.=3D20
>=3D20
> Can anyone help a friend of mine who acquired lots of cone 06 clay to mak=
e=3D
it withstand raku firing. Would playground sand work he needs to keep dow=
n=3D
expenses down! Can you suggest percentages. He will be adding whatever it=
i=3D
s to moist clay.Thanks in advance. Happy rest of summer all.=3D20
> Veena
>=3D20
> Sent from my iPhone
ronroy@CA.INTER.NET on sat 18 aug 12
Hi Veena,
I concur with Paul - I would not recommend sand - first because it may
not all be sand and also because - as those chunks of quartz go
through the quartz inversion at 573C they get smaller - fast. That
means if a rim cools faster than a foot - and tries to get smaller
because of the quartz there is going to be cracking.
Kyanite is not that expensive by the way - 40 mesh would work well if
they are not throwing it - use 100 mesh if for working on the wheel.
RR
Quoting Gerholdclay :
> Recommend adding kyanite 30-35 mesh at 10 percent and 100 mesh grog
> to a max of 10 percent. This assumes clay is not already frogged in
> which case just use the Kyanite. Of course the normal caveats about
> testing apply.
>
> Paul
>
> Sent from my iPad
>
> On Aug 17, 2012, at 3:57 PM, veenaraghavan wrote:
>
>> Hi folks.
>>
>> Can anyone help a friend of mine who acquired lots of cone 06 clay
>> to make it withstand raku firing. Would playground sand work he
>> needs to keep down expenses down! Can you suggest percentages. He
>> will be adding whatever it is to moist clay.Thanks in advance.
>> Happy rest of summer all.
>> Veena
>>
>> Sent from my iPhone
>
Ben Morrison on sat 18 aug 12
From the research I've done Mullite is a good material to use=3D
Ron Roy,=3D0A=3D0AFrom the research I've done Mullite is a good material to=
use=3D
as well, though not as good as Kyanite. Would you concur Ron, or is there =
=3D
a reason to not use mullite grog?=3D0A=3D0A-Ben Morrison=3D0A=3D0A=3D0A____=
__________=3D
__________________=3D0A From: "ronroy@CA.INTER.NET" =
=3D0AT=3D
o: Clayart@LSV.CERAMICS.ORG =3D0ASent: Saturday, August 18, 2012 10:38 AM=
=3D0AS=3D
ubject: Re: What to add to cone 06 clay for firing in raku=3D0A =3D0AHi Vee=
na,=3D
=3D0A=3D0AI concur with Paul - I would not recommend sand - first because i=
t ma=3D
y=3D0Anot all be sand and also because - as those chunks of quartz go=3D0At=
hrou=3D
gh the quartz inversion at 573C they get smaller - fast. That=3D0Ameans if =
a =3D
rim cools faster than a foot - and tries to get smaller=3D0Abecause of the =
qu=3D
artz there is going to be cracking.=3D0A=3D0AKyanite is not that expensive =
by t=3D
he way - 40 mesh would work well if=3D0Athey are not throwing it - use 100 =
me=3D
sh if for working on the wheel.=3D0A=3D0ARR=3D0A=3D0A=3D0AQuoting Gerholdcl=
ay dclay@DISHMAIL.NET>:=3D0A=3D0A> Recommend adding kyanite 30-35 mesh at 10 p=
erce=3D
nt and 100 mesh grog=3D0A> to a max of 10 percent.=3DA0 This assumes clay i=
s no=3D
t already frogged in=3D0A> which case just use the Kyanite.=3DA0 Of course =
the =3D
normal caveats about=3D0A> testing apply.=3D0A>=3D0A> Paul=3D0A>=3D0A> Sent=
from my i=3D
Pad=3D0A>=3D0A> On Aug 17, 2012, at 3:57 PM, veenaraghavan S.CO=3D
M> wrote:=3D0A>=3D0A>> Hi folks.=3D0A>>=3D0A>> Can anyone help a friend of =
mine who=3D
acquired lots of cone 06 clay=3D0A>> to make it withstand raku firing. Wou=
ld=3D
playground sand work=3DA0 he=3D0A>> needs to keep down expenses down! Can =
you =3D
suggest percentages.=3DA0 He=3D0A>> will be adding whatever it is to moist =
clay=3D
.Thanks in advance.=3D0A>> Happy rest of summer all.=3D0A>> Veena=3D0A>>=3D=
0A>> Sen=3D
t from my iPhone=3D0A>
ronroy@CA.INTER.NET on sun 19 aug 12
Hi Ben,
Mullite might be a good addition but I have no experience with it - =3D20
sounds like the subject could be the basis of an informative set of =3D20
experiments - anyone who would like to do that can count on me to do =3D20
any dilatometry needed.
RR
Quoting Ben Morrison :
> From the research I've done Mullite is a good material to use
> Ron Roy,
>
> From the research I've done Mullite is a good material to use as =3D20
> well, though not as good as Kyanite. Would you concur Ron, or is =3D20
> there a reason to not use mullite grog?
>
> -Ben Morrison
>
>
> ________________________________
> From: "ronroy@CA.INTER.NET"
> To: Clayart@LSV.CERAMICS.ORG
> Sent: Saturday, August 18, 2012 10:38 AM
> Subject: Re: What to add to cone 06 clay for firing in raku
>
> Hi Veena,
>
> I concur with Paul - I would not recommend sand - first because it may
> not all be sand and also because - as those chunks of quartz go
> through the quartz inversion at 573C they get smaller - fast. That
> means if a rim cools faster than a foot - and tries to get smaller
> because of the quartz there is going to be cracking.
>
> Kyanite is not that expensive by the way - 40 mesh would work well if
> they are not throwing it - use 100 mesh if for working on the wheel.
>
> RR
>
>
> Quoting Gerholdclay :
>
>> Recommend adding kyanite 30-35 mesh at 10 percent and 100 mesh grog
>> to a max of 10 percent.=3DA0 This assumes clay is not already frogged in
>> which case just use the Kyanite.=3DA0 Of course the normal caveats about
>> testing apply.
>>
>> Paul
>>
>> Sent from my iPad
>>
>> On Aug 17, 2012, at 3:57 PM, veenaraghavan wrot=
=3D
e:
>>
>>> Hi folks.
>>>
>>> Can anyone help a friend of mine who acquired lots of cone 06 clay
>>> to make it withstand raku firing. Would playground sand work=3DA0 he
>>> needs to keep down expenses down! Can you suggest percentages.=3DA0 He
>>> will be adding whatever it is to moist clay.Thanks in advance.
>>> Happy rest of summer all.
>>> Veena
>>>
>>> Sent from my iPhone
>>
>
Ben Morrison on mon 20 aug 12
Well I just happen to have a several hundred pound pile of mullite in my st=
=3D
orage area, so if I ever get a chance I'll mix someone and pop it off.=3D0A=
=3D
=3D0A=3D0A-Ben=3D0A=3D0A=3D0A________________________________=3D0A From: "r=
onroy@CA.INT=3D
ER.NET" =3D0ATo: Clayart@LSV.CERAMICS.ORG =3D0ASent: S=
unda=3D
y, August 19, 2012 9:39 AM=3D0ASubject: Re: What to add to cone 06 clay for=
f=3D
iring in raku=3D0A =3D0AHi Ben,=3D0A=3D0AMullite might be a good addition b=
ut I hav=3D
e no experience with it -=3DA0 =3D0Asounds like the subject could be the ba=
sis =3D
of an informative set of=3DA0 =3D0Aexperiments - anyone who would like to d=
o th=3D
at can count on me to do=3DA0 =3D0Aany dilatometry needed.=3D0A=3D0ARR=3D0A=
=3D0A=3D0AQuot=3D
ing Ben Morrison :=3D0A=3D0A> From the research I've d=
one =3D
Mullite is a good material to use=3D0A> Ron Roy,=3D0A>=3D0A> From the resea=
rch I'=3D
ve done Mullite is a good material to use as=3DA0 =3D0A> well, though not a=
s go=3D
od as Kyanite. Would you concur Ron, or is=3DA0 =3D0A> there a reason to no=
t us=3D
e mullite grog?=3D0A>=3D0A> -Ben Morrison=3D0A>=3D0A>=3D0A> _______________=
__________=3D
_______=3D0A>=3DA0 From: "ronroy@CA.INTER.NET" =3D0A> =
To: Cl=3D
ayart@LSV.CERAMICS.ORG=3D0A> Sent: Saturday, August 18, 2012 10:38 AM=3D0A>=
Sub=3D
ject: Re: What to add to cone 06 clay for firing in raku=3D0A>=3D0A> Hi Vee=
na,=3D
=3D0A>=3D0A> I concur with Paul - I would not recommend sand - first becaus=
e it=3D
may=3D0A> not all be sand and also because - as those chunks of quartz go=
=3D0A=3D
> through the quartz inversion at 573C they get smaller - fast. That=3D0A> =
me=3D
ans if a rim cools faster than a foot - and tries to get smaller=3D0A> beca=
us=3D
e of the quartz there is going to be cracking.=3D0A>=3D0A> Kyanite is not t=
hat =3D
expensive by the way - 40 mesh would work well if=3D0A> they are not throwi=
ng=3D
it - use 100 mesh if for working on the wheel.=3D0A>=3D0A> RR=3D0A>=3D0A>=
=3D0A> Quot=3D
ing Gerholdclay :=3D0A>=3D0A>> Recommend adding k=
yani=3D
te 30-35 mesh at 10 percent and 100 mesh grog=3D0A>> to a max of 10 percent=
.=3D
=3DA0 This assumes clay is not already frogged in=3D0A>> which case just us=
e th=3D
e Kyanite.=3DA0 Of course the normal caveats about=3D0A>> testing apply.=3D=
0A>>=3D
=3D0A>> Paul=3D0A>>=3D0A>> Sent from my iPad=3D0A>>=3D0A>> On Aug 17, 2012,=
at 3:57 P=3D
M, veenaraghavan wrote:=3D0A>>=3D0A>>> Hi folks.=3D0=
A>>>=3D
=3D0A>>> Can anyone help a friend of mine who acquired lots of cone 06 clay=
=3D
=3D0A>>> to make it withstand raku firing. Would playground sand work=3DA0 =
he=3D
=3D0A>>> needs to keep down expenses down! Can you suggest percentages.=3DA=
0 He=3D
=3D0A>>> will be adding whatever it is to moist clay.Thanks in advance.=3D0=
A>>>=3D
Happy rest of summer all.=3D0A>>> Veena=3D0A>>>=3D0A>>> Sent from my iPhon=
e=3D0A>>=3D
=3D0A>
Gerholdclay on mon 20 aug 12
I have tried both Kyanite and Mullite and in my experience Kyanite is super=
i=3D
or in reducing cracking in difficult shapes. I have no rational for differ=
e=3D
nce except my experience.
Paul
Sent from my iPad
On Aug 18, 2012, at 5:02 PM, Ben Morrison wrote:
> =3D46rom the research I've done Mullite is a good material to use
> Ron Roy,
>=3D20
> =3D46rom the research I've done Mullite is a good material to use as well=
, t=3D
hough not as good as Kyanite. Would you concur Ron, or is there a reason to=
n=3D
ot use mullite grog?
>=3D20
> -Ben Morrison
>=3D20
>=3D20
> ________________________________
> From: "ronroy@CA.INTER.NET"
> To: Clayart@LSV.CERAMICS.ORG=3D20
> Sent: Saturday, August 18, 2012 10:38 AM
> Subject: Re: What to add to cone 06 clay for firing in raku
>=3D20
> Hi Veena,
>=3D20
> I concur with Paul - I would not recommend sand - first because it may
> not all be sand and also because - as those chunks of quartz go
> through the quartz inversion at 573C they get smaller - fast. That
> means if a rim cools faster than a foot - and tries to get smaller
> because of the quartz there is going to be cracking.
>=3D20
> Kyanite is not that expensive by the way - 40 mesh would work well if
> they are not throwing it - use 100 mesh if for working on the wheel.
>=3D20
> RR
>=3D20
>=3D20
> Quoting Gerholdclay :
>=3D20
>> Recommend adding kyanite 30-35 mesh at 10 percent and 100 mesh grog
>> to a max of 10 percent. This assumes clay is not already frogged in
>> which case just use the Kyanite. Of course the normal caveats about
>> testing apply.
>>=3D20
>> Paul
>>=3D20
>> Sent from my iPad
>>=3D20
>> On Aug 17, 2012, at 3:57 PM, veenaraghavan wrote:
>>=3D20
>>> Hi folks.
>>>=3D20
>>> Can anyone help a friend of mine who acquired lots of cone 06 clay
>>> to make it withstand raku firing. Would playground sand work he
>>> needs to keep down expenses down! Can you suggest percentages. He
>>> will be adding whatever it is to moist clay.Thanks in advance.
>>> Happy rest of summer all.
>>> Veena
>>>=3D20
>>> Sent from my iPhone
>>=3D20
Rimas VisGirda on mon 20 aug 12
I'm not sure you can add anything to a clay that vitrifies at C/06 to make =
it work for raku... The very nature of raku is that a clay body needs to be=
"soft" at raku temperatures (aka bisque temperatures). That is a high-fire=
body is fired to bisque temperatures -raku temperatures are pretty much bi=
sque temperatures. The whole thing is possible because the H-F body is "sof=
t" at bisque and will withstand the thermal shocks associated with coming f=
rom 1900F to 50-100F in a matter of seconds. Any body that becomes "hard" w=
ill not be able to withstand that shock. Hence no matter what you add to a =
cone 06 clay, if the clay gets "hard" it will crack. Quartz inversion also =
doesn't have any effect on cracking in a "raku" (read high-fire) body as H-=
F bodies are "soft" at bisque and can absorb the shock; quartz inversion on=
ly matters if a piece is vitrified ("hard"). The corollary to that is that =
in a typical high fire the (glazed) ware is still bisque (soft) past
quartz inversion on the way up, but is vitrified (hard) on the way down; h=
ence it is never necessary to go slow past quartz inversion on the way up b=
ut can be useful in some cases on the way down. In my opinion adding sand o=
r grog to a cone 06 body will not make it suitable for raku; about the only=
thing that would make it suitable would be to add high fire clay and the a=
mount of H-F clay to make it suitable could be determined by testing... Add=
ing sand or grog would improve its dry strength and drying properties but w=
ould not affect the "hardness" or "softness" of the clay itself at cone 05-=
06...
Way back when, a friend wanted to achieve "raku" effects on high-fired work=
. He would fire the unglazed piece to cone 10 then apply low-fire (raku) gl=
azes and proceed to fire and perform the typical post firing reduction. His=
pieces always cracked; sometimes not completely in half but always some st=
ructural crack...
Another factor that demonstrates the typical raku "crackle" or "crazing" is=
that if you take any high fire body; bisque it; glaze it with a low-fire, =
C/05 glaze, and fire it to cone 05 it will automatically crackle. The crack=
le on a cone 6 body will in general be finer than the crackle on a cone 10 =
body, and I would speculate that the crackle on a heavily grogged C/10 body=
would be even coarser... Which brings to mind the difference between "crac=
kle" and "crazing" -my supposition is that it's crackle if you like it; and=
crazing if you don't like it...
Regarding quartz inversion, my personal experience is that it doesn't matte=
r how fast I fire and how fast I cool in the initial cone 10 firing. I only=
have problems with cracking on plates with repeated C/05 and C/018 firings=
; my plates, especially larger plates 15" or wider, would crack anywhere be=
tween the 2nd to 6th firing. Since I started going slow past quartz inversi=
on I no longer get the cracks. Only plates seem to be affected, my pots and=
sculptures seem to withstand multiple firings without slowing at quartz in=
version...
Have a nice day, -Rimas
Rimas VisGirda on mon 20 aug 12
=3D0A=3D0AWell, I'm not sure how to answer you... in MY experience I have f=
ound=3D
no difference in opening a body with either sand or grog. I'm not sure wha=
=3D
t you refer to as free quartz, is that silica sand or the SiO2 in the Al2O3=
=3D
SiO2-6H2O in the idealized clay molecule. I have always thought that quartz=
=3D
inversion problems came from the microscopic Si in the molecule not in the=
=3D
"rock" that is sand... and that (I have empirically found) adding any aggr=
=3D
egate, whether sand or grog, doesn't do much other than reduce plasticity a=
=3D
nd increase drying properties and provide=3DA0 more dry strength. But then,=
I=3D
don't have a lab and have been pretty much doing things by the seat of my =
=3D
pants for the last 40-50 years. I have no scientific basis or data to confi=
=3D
rm my suspicions and assumptions, although I WAS a rocket scientist in a fo=
=3D
rmer life. My "theories" have always worked for me, and as someone said -if=
=3D
the foo shits, wear it... But maybe that's JUST in MY situations...
Regards, -Rimas=3D0A=3D0AFrom: "ronroy@ca.inter.net" =
=3D0A=3D
=3D0AI'm having some trouble understanding what you mean with the following=
s=3D
tatement=3D0A=3D0A"Quartz inversion also doesn't=3D0A> have any effect on c=
rackin=3D
g in a "raku" (read high-fire) body as H-F bodies are "soft" at bisque and =
=3D
can absorb the shock;"=3D0A=3D0AAre you saying there is no possibility of b=
isqu=3D
e dunting around 573C due to free quartz?=3D0A=3D0AIf so - my experience is=
to =3D
the contrary - glad to discuss this further if you don't agree.=3D0A=3D0ARR
ronroy@CA.INTER.NET on tue 21 aug 12
Hi Rimas,
I do understand that some potters use sand in their clay bodies and =3D20
that they have no trouble. I just don't think it's the best thing to =3D20
do when compared with grog or kyanite.
All the quartz in a clay body goes through an inversion at 573C - it =3D20
dos not matter what size it is. In porcelain (which normally has about =3D2=
0
25% fine silica) bisque dunting can become a particular problem during =3D2=
0
cool down. Foot of pot in contact with a hot shelf - rim cools faster =3D20
- rim tries to contract because of the quartz getting smaller at 573C =3D20
- pot cracks.
These are the the kind of cracks that are hard to see because - when =3D20
the foot goes through the quartz inversion the crack closes up.
This can happen with any clay with enough free quartz in it - usually =3D20
to large platters and bowls. I would think that it might be a problem =3D20
with raku - especially large items - with the sudden cooling. That is =3D20
why I don't recommend silica sand - because it adds to the total =3D20
quartz load in any body.
Perhaps your question about the micro fine silica is related to the =3D20
problem of cristobalite production in high fired stoneware - there is =3D20
a very fine article on that subject on the Studio Potter web site - by =3D2=
0
Peter Sohngen - certainly worth a look.
http://studiopotter.org/pdfs/Sohng%20pps84-89.pdf
You might also find the photograph on Page 82 of Ceramic Masterpieces =3D20
by Kingery and Vandiver (ISBN 0-02-918480-0) showing a grain of quartz =3D2=
0
in a fired clay body. The quartz has gone through it's inversion and =3D20
when it got smaller it has moved away from the surrounding clay so =3D20
that there is a gap between the quartz and the clay.
Now I'm not sure my intuition is correct in this but - it looks to me =3D20
like a body full of those gaps - if there are enough of them - would =3D20
be weaker over all.
Anyway - happy to discuss this subject further - even to the point of =3D20
doing some experiments to augment our understanding.
RR
Quoting Rimas VisGirda :
>
>
> Well, I'm not sure how to answer you... in MY experience I have =3D20
> found no difference in opening a body with either sand or grog. I'm =3D20
> not sure what you refer to as free quartz, is that silica sand or =3D20
> the SiO2 in the Al2O3SiO2-6H2O in the idealized clay molecule. I =3D20
> have always thought that quartz inversion problems came from the =3D20
> microscopic Si in the molecule not in the "rock" that is sand... and =3D2=
0
> that (I have empirically found) adding any aggregate, whether sand =3D20
> or grog, doesn't do much other than reduce plasticity and increase =3D20
> drying properties and provide=3DA0 more dry strength. But then, I don't =
=3D20
> have a lab and have been pretty much doing things by the seat of my =3D20
> pants for the last 40-50 years. I have no scientific basis or data =3D20
> to confirm my suspicions and assumptions, although I WAS a rocket =3D20
> scientist in a former life. My "theories" have always worked for me, =3D2=
0
> and as someone said -if the foo shits, wear it... But maybe that's =3D20
> JUST in MY situations...
> Regards, -Rimas
>
> From: "ronroy@ca.inter.net"
>
> I'm having some trouble understanding what you mean with the =3D20
> following statement
>
> "Quartz inversion also doesn't
>> have any effect on cracking in a "raku" (read high-fire) body as =3D20
>> H-F bodies are "soft" at bisque and can absorb the shock;"
>
> Are you saying there is no possibility of bisque dunting around 573C =3D2=
0
> due to free quartz?
>
> If so - my experience is to the contrary - glad to discuss this =3D20
> further if you don't agree.
>
> RR
>
veenaraghavan@cs.com on wed 22 aug 12
I want to thank everyone for taking the time to respond to my query on beha=
=3D
lf of a friend. I have passed all the information on to him and he is now d=
=3D
eciding what to do.
I have also passed on some of the subsequent information that followed as =
=3D
the subject morphed.=3D20
Thank you one and all for your input.
All the best.
Veena
veenaraghavan@cs.com
Lee on thu 23 aug 12
On Thu, Aug 23, 2012 at 12:14 PM, Rimas VisGirda wrote:
> But this has strayed from the original question... I still think that no =
=3D
matter what you put into a cone 06 clay it will still
> be problematical as the clay gets "hard" at cone 06 and won't have the re=
=3D
siliency to absorb the thermal shock...
Rimas, What kind of "cone 06" are you talking about? How will you
fire the clay?
I am blending fireclay with Helmer's to get a mogusa (clay used with
Shino clay bodies.) My mogusa in Mashiko was not vitrified after
firing to cone 13. The Tea masters like the underfired shino clay
body because it sounded "soft" like raku when a bamboo tea whisk is
used in it.
--=3D20
--
Lee Love in Minneapolis
http://mingeisota.blogspot.com/
"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D97tha=
t is, "T=3D
he
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue
Rimas VisGirda on thu 23 aug 12
Hi RR,
RR: I do understand that some potters use sand in their clay bodies and tha=
t they have no trouble. I just don't think it's the best thing to do when c=
ompared with grog or kyanite.
RTV: OK, I use grog and sand. Don't know what kyanite is... I guess I'm a l=
uddite in that respect, the stuff I learned to use in the 60's still serves=
me well...
RR: All the quartz in a clay body goes through an inversion at 573C - it do=
s not matter what size it is. In porcelain (which normally has about 25% fi=
ne silica) bisque dunting can become a particular problem during cool down.=
Foot of pot in contact with a hot shelf - rim cools faster - rim tries to =
contract because of the quartz getting smaller at 573C - pot cracks.
RTV: yes, I suppose it does, for some reason i never assosiated the sand as=
part of the quartz inversion equation. I understand the theory but I've be=
en using porcelain (with and without sand) for quite a while and have never=
had cracking problems from bisque. And, as I said in my first? post, actua=
lly never any problems except with multiple firings of plates typically lar=
ger than 15" diameter...
RR: These are the the kind of cracks that are hard to see because - when th=
e foot goes through the quartz inversion the crack closes up. This can happ=
en with any clay with enough free quartz in it - usually to large platters =
and bowls. I would think that it might be a problem with raku - especially =
large items - with the sudden cooling. That is why I don't recommend silica=
sand - because it adds to the total quartz load in any body. Perhaps your =
question about the micro fine silica is related to the problem of cristobal=
ite production in high fired stoneware - there is a very fine article on th=
at subject on the Studio Potter web site - by Peter Sohngen - certainly wor=
th a look.
http://studiopotter.org/pdfs/Sohng%20pps84-89.pdf
You might also find the photograph on Page 82 of Ceramic Masterpieces by Ki=
ngery and Vandiver (ISBN 0-02-918480-0) showing a grain of quartz in a fire=
d clay body. The quartz has gone through it's inversion and when it got sma=
ller it has moved away from the surrounding clay so that there is a gap bet=
ween the quartz and the clay.
Now I'm not sure my intuition is correct in this but - it looks to me like =
a body full of those gaps - if there are enough of them - would be weaker o=
ver all.
Anyway - happy to discuss this subject further - even to the point of doing=
some experiments to augment our understanding.
RTV: OK, probably shouldn't have gotten into this thread... I'm not much in=
terested in the science behind clay and glazes, I do what I do because it w=
orks for me, i.e. if it ain't broke, don't fix it... I did some glaze calc =
way back when in beginning ceramics but didn't see much sense in pursuing i=
t, the glazes I made weren't that exceptional and the "class" glazes worked=
just fine; still use the clear... When I started getting the plates cracki=
ng at multiple firings I slowed at quartz inversion as well as lifting them=
off the kiln shelf... You may be right in all you espouse and I may just b=
e lucky.
But this has strayed from the original question... I still think that no ma=
tter what you put into a cone 06 clay it will still be problematical as the=
clay gets "hard" at cone 06 and won't have the resiliency to absorb the th=
ermal shock... Regards, -Rimas
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