Annabelle on sat 28 apr 01
My friend is having a problem with her new de-airing pug mill. 50 % of =3D
her pots over 10 lbs
have a groove in the base, about one inch from the edge. This is not the =
=3D
result of folding the clay down to the wheel head, creating another wall =
=3D
and trapping air between two walls. Any one know the cause of this?
Pugs are placed side down. Stoneware body, same she's made forever. =3D
This is her 3rd
pugmill, 1st de-airing. She throws to a finished weight, so trimming is =
=3D
not an option here. Same claybody in her other pug mill no problems. =3D
Thanks for any help, checked the archives first but didn''t find =3D
anything like this.....
Annabelle in Naples Fl.
Bert Stevens on sat 28 apr 01
you still need to wedge larger pieces, even de-aired clay..helps line th=
e
clay particles up for the torque from the wheel
----- Original Message -----
From: "Annabelle"
To:
Sent: Saturday, April 28, 2001 9:07 AM
Subject: Problem throwing de-aired clay
My friend is having a problem with her new de-airing pug mill. 50 % of h=
er
pots over 10 lbs
have a groove in the base, about one inch from the edge. This is not the
result of folding the clay down to the wheel head, creating another wall =
and
trapping air between two walls. Any one know the cause of this?
Pugs are placed side down. Stoneware body, same she's made forever. Th=
is
is her 3rd
pugmill, 1st de-airing. She throws to a finished weight, so trimming is =
not
an option here. Same claybody in her other pug mill no problems. Thanks f=
or
any help, checked the archives first but didn''t find anything like
this.....
Annabelle in Naples Fl.
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iandol on sun 29 apr 01
Dear Annabelle,
This is not an unusual fault and I have met potters who were plagued by =3D
it from time to time. When I suffered it I sorted out an answer. These =3D
are my own thoughts.
I believe this fault arises during centring when insufficient downward =3D
force is exerted to counter the force exerted inwards at the wheelhead =3D
or bat. It can happen during the intial push to centre the clay or when =3D
collaring at the base to overcome spread due to slumping after the pug =3D
has been opened and wall raised. A strong inward force causes clay =3D
across the periphery of the base to fold upward as clay in the outer =3D
layer at the bottom of the wall is crushed inwards. In doing so clay =3D
tears or detaches from the wheel head. The effect is to create a void. =3D
It can be an annular cavity around the edge or a cone at the centre.
I would not like to criticise your friends throwing technique. But if =3D
she centres by using the style shown in "Pottery on the Wheel" by =3D
Elsbeth Woody where the first motion is to force clay inwards at the =3D
base, this fault is prone to occur when throwing large masses. The other =
=3D
books always show small lumps of clay. If it is happening when she is =3D
collaring the base inward then a firm hand is needed inside the pot =3D
giving a strong downward push and create a squeeze.
Unfortunately, the mechanics of throwing are little understood and the =3D
ways which are demonstrated and taught are possibly inefficient.
I suggest you have a look in Pottery Making Illustrated, Fall 2000. at =3D
an article "The Dynamic Art of Trowing Clay" which illustrates how this =3D
and other similar faults can happen.
If you need further information, get in touch.
Best regards,
Ivor Lewis. Redhill, South Australia.
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