iandol on fri 13 apr 01
As I mentioned in a previous post, this week my research topic is the =
notorious "S" crack.
I require samples of clay bodies which have shown themselves to be prone =
to throw this defect on a habitual basis, like almost with every pot. A =
clay will qualify even if it only shows one of those slight linear =
cracks in the centre after firing, but it must be prone to this disease. =
It is also important that the clay is in the unfired state. I require =
about 5 - 10 gms for microscopic examination and as much information you =
can give me about the content of the clay. I realise this may be =
difficult to obtain if it is a proprietary material and I do not wish to =
get into arguments with any clay manufacturer, so please keep your =
sample anonymous.
If any of you are in a position to assist by sending samples, please =
contact me off list. Your assistance will be appreciated.
Best regards,
Ivor Lewis, Redhill, South Australia.
iandol on sat 14 apr 01
Dear Des,
I appreciate your description of your working methods and I know they =
are great ways of getting superb clay. John Richter uses some of those =
ideas for his native clays. But if you rarely get any form of cracking =
then your samples would not reveal the nature of the beast which causes =
cracks. From the sounds of things with method 1, excessive spiral =
wedging could lead to segregation, an effect which I suspect may have =
some bearing on the problem.
I need clays which are know to crack. For example, and I wish I had kept =
some of the stuff, I had half a ton from from Bennet about twenty years =
ago. Almost every pot cracked in the base. Clay from the other end of =
the cut was perfect.
Nevertheless, Thanks for your input. It is appreciated
Des Howard on sat 14 apr 01
Ivor
Sorry, no worthy samples, just history.
We have made clay bodies by:
1. Hand blunging slip then onto air dried cloth lined troughs, ramshorn
wedged before storage then extensive spiral wedging before use.
2. Thick slurry in a doughmixer, cow pattied onto plaster slabs
on a slow woodfired drying oven, rolled into jam roll, horseshoed,
then air dried before storage, then extensive spiral wedging before use.
3. Dry mixed to throwing consistency in a doughmixer,
non de-airing pugged before storage, reasonable spiral wedging before use.
4. Currently, lengthy mechanical blunging, filter pressed, non de-airing
pugged, stored, occasional token spiral wedging before use.
I spiral wedge clockwise, Trev, spiral wedges counter clockwise.
We get the occasional linear crack in thrown items,
none in extruded or jiggered items.
No "S" cracks, the only times I have had "S" cracks
were in hump thrown items.
About 80% cracked, dropped to about 5% when a broom handle
stub was used to compress the inside of foot rings after turning.
These cracks occurred while using the 1. method of making clay.
Des
iandol wrote:
> As I mentioned in a previous post, this week my research topic is the notorious "S" crack.
> I require samples of clay bodies which have shown themselves to be prone to throw this defect on a habitual basis, like almost with every pot. A clay will qualify even if it only shows one of those slight linear cracks in the centre after firing, but it must be prone to this disease. It is also important that the clay is in the unfired state. I require about 5 - 10 gms for microscopic examination and as much information you can give me about the content of the clay. I realise this may be difficult to obtain if it is a proprietary material and I do not wish to get into arguments with any clay manufacturer, so please keep your sample anonymous.
> If any of you are in a position to assist by sending samples, please contact me off list. Your assistance will be appreciated.
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.lisp.com.au
Chris Clarke on tue 17 apr 01
Ivor,
Where do we send you a sample, I deleted by accident. And how much
again. chris
chris@ccpots.com
www.ccpots.com
----- Original Message -----
From: iandol
To:
Sent: Friday, April 13, 2001 11:25 PM
Subject: "S" Crack research
Dear Des,
I appreciate your description of your working methods and I know they are
great ways of getting superb clay. John Richter uses some of those ideas =
for
his native clays. But if you rarely get any form of cracking then your
samples would not reveal the nature of the beast which causes cracks. Fro=
m
the sounds of things with method 1, excessive spiral wedging could lead t=
o
segregation, an effect which I suspect may have some bearing on the probl=
em.
I need clays which are know to crack. For example, and I wish I had kept
some of the stuff, I had half a ton from from Bennet about twenty years a=
go.
Almost every pot cracked in the base. Clay from the other end of the cut =
was
perfect.
Nevertheless, Thanks for your input. It is appreciated
_________________________________________________________________________=
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