Cat81257@AOL.COM on thu 1 jun 00
Hi Ivor..... you got a good point going there .... I have a friend that
runs her fingers back and forth back and forth and ribs the bottom of wide
stuff... myself after I open up abit and before I get to the thickness I
want bottom to be I use the blunt end of the screw driver I use to get bats
off to pound down the middle in hopes that this is compressing the darn
thing .... also use ribs thru the process.... yup kinda fussy about it
all thru but havent had a s crack in eons .... maybe overdone but dang
cant even remember last time I had a S crack....cant recall having problems
with s cracks prior to doing this either LOL guess my brain is full
teacher ... could be I got lucky or maybe its been so dang long ( over 20
yrs) that I just dont recall .. but I do believe that even if I was lucky
prior to this I'd eventually have problems with platters , plates and
anything wide..... on handbuilt stuff where I add walls or some such to
slab bottoms I find that if I wait till everything is equal moisture
before attaching NO problemo with cracks either .... sometimes just leaving
them to sit covered together overnite does this ... guess this would come
under the heading of tension vs compression on thrown items .....
Dont think I've added much to the discussion as far as factual scientific
stuff but just my 2 cents worth as a production potter thats been at it
for 20 yrs plus.... on the job observation so to speak... respectfully
submitted :o) Cat
Dennis, Rhonda, Rachel Oldland on thu 1 jun 00
Hey Ivor,
The book was the potter's primer by Morgen Hall.
I occasionally look through my library of gift books, and collected books
whenever I have a problem . This is found on page 99, under the soup bowl,
step number 9.
Best Regards, Rhonda
At 14:12 6/1/00 +0930, you wrote:
>Subject: s-shaped cracks update
>
>I suppose every one who throws clay for a prolonged period will at some
time or other run into the problem of S-cracks. Perhaps Rhonda Oldland
would give more information about the clay primer from which she quotes to
describe a way of tensioning the base of a pot. The term Tension is a
change from Compress. I know about the technique she describes but have
always found that when I apply the sort of pressure which I discern is
needed I finish up with my finger or thumb going through the clay to the
wheelhead if I move from the centre to the inner base of the wall.
>
>There is another thing which continues to concern me. It is descriptions
of the way clay particles align themselves as parallel sheets in response
to pressure. Although there are idealised diagrams in several books which
show this, not one author has come forward with photomicrographs of unfired
pots which clearly illustrate that this happens as a fact. Therefore I tend
to consider their information to be assumption, conjecture or imaginative.
>
>Like Rhonda, I have an open mind on the matter, until better evidence is
presented. But having said that, I find it difficult to accept that
platelets of clay in any clay body (which may have more than forty percent
non plastics whose particle size is two or three orders of magnitude
greater, that is a hundred to one thousand times the size of clay
particles) are going to respond to pressure from a thumb which has an area
a million times larger that that of the majority of clay crystals.
>
>Should anyone wish to take this discussion further I would be pleased hear
what they have to say.
>
>Ivor Lewis. Often doing things in a contrary way to gain understanding.
>
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