Lili Krakowski on fri 12 may 06
May writes:
" The goal is to have
mature tin glaze for terra-cotta , without lead and
fires at 1140 C. She has lead fritted tin glaze, which
is not a problem, but she does not want to use it
anymore for her functional pieces. With the non-leaded
tin glaze, the vases are leaking with water and
customers are returning the goods."
Something here does not ring a bell.
A glaze does add some water resistance to a pot. Some. But it is NOT a
waterproofing.
I assume that a thick layer of a dense glaze will indeed delay the
absorption of moisture by the body. But not forever.
Where footrims for instance are not glazed water will seep in--esp on ware
that is used and washed.
My guess here--and I hope some of our experts will chime in--is that the
body is not well matured. As I wrote the other day I have seen listings of
some commercial bodies with VERY low absorption.
Has your friend, May, made tests of the absorption of her fired clay?
Because I think that is part of the problem....And I think it possible that
the lead glazes seeped more into the body, maturing it a bit more, and that
the leadless glaze does not interact as actively....Tom,Ron, John, Ivor,
Mmmmmmmmmmm?
Lili Krakowski
Ivor and Olive Lewis on sat 13 may 06
Dear Lili Krakowski,=20
As I point out in my previous post, Earthenware products are glazed all =
over, including the footring and the underside of the base. They are =
supported in the kiln on Star Spurs and Stilts made from vitreous but =
unglazed porcelain. If the glaze is thin these break away and leave an =
impervious scar. Because the glaze sometimes breaks with a razor edge =
these scars are honed with a carborundum brick.
Did this over a two year period with Bob Mason at New Silksworth in the =
mid sixties. When I crossed over to Sunderland Art School I had to learn =
the whole new caper of waxing bottoms because were firing stoneware.
On the bases of some commercial flatware you will find three scars. This =
even applies to bone china and porcelain where the high bisque fire low =
glost firing process is used. It is something other potters might =
meditate on as a way of getting a high quality finish.
Enjoy the moment.
Best regards,
Ivor
Malcolm Schosha on sun 14 may 06
--- In clayart@yahoogroups.com, Ivor and Olive Lewis
wrote:
>
> Dear Lili Krakowski,
>
> As I point out in my previous post, Earthenware products are glazed
all over, including the footring and the underside of the base. They
are supported in the kiln on Star Spurs and Stilts made from vitreous
but unglazed porcelain. If the glaze is thin these break away and
leave an impervious scar. Because the glaze sometimes breaks with a
razor edge these scars are honed with a carborundum brick.
>
> Did this over a two year period with Bob Mason at New Silksworth in
the mid sixties. When I crossed over to Sunderland Art School I had
to learn the whole new caper of waxing bottoms because were firing
stoneware.
>
> On the bases of some commercial flatware you will find three scars.
This even applies to bone china and porcelain where the high bisque
fire low glost firing process is used. It is something other potters
might meditate on as a way of getting a high quality finish.
>
.............................
Ivor,
In Italy, every place I ever worked made earthenware and cleaned the
glaze from the foot before firing.
This can be easily done by soaking a piece of foam rubber 1/2" - 1"
thick, by at least 12" wide, by as long as you want (but at least
24",) and putting it on a flat surface. Wiping the foot of the pot
lightly over this wet foam rubber easily and quickly cleans the foot.
No latex is needed.
Malcolm
Ivor and Olive Lewis on mon 15 may 06
Dear Malcolm Schosha,=20
I did not say that it could not be done or that it should not be done. I =
just pointed out what I had leaned from my experience.=20
We have a suite of bone china table ware. The flat wares have all been =
fired on stilts. The containers are dry footed.
What was the adsorption rate of the wares you were firing at those =
Italian factories? Was your work declared safe for use in a microwave =
oven?
Best regards,
Ivor
Malcolm Schosha on mon 15 may 06
Hi Ivor,
I did not mean to give the impression that I think what you described
was wrong(if there is such a thing as 'wrong' when methods, and
individual intent, and circumstances vary so much). I was just
describing what I saw done in Italy.
Be well.
Malcolm
...................................
--- In clayart@yahoogroups.com, Ivor and Olive Lewis
wrote:
>
> Dear Malcolm Schosha,
>
> I did not say that it could not be done or that it should not be
done. I just pointed out what I had leaned from my experience.
>
> We have a suite of bone china table ware. The flat wares have all
been fired on stilts. The containers are dry footed.
>
> What was the adsorption rate of the wares you were firing at those
Italian factories? Was your work declared safe for use in a microwave
oven?
>
> Best regards,
>
> Ivor
>
>
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