iandol on mon 8 may 00
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----------------------------Original message---------------------------- =
Jean
Todd wrote: In Australia long before plastic pipes came along our sewer =
pipes
were made of terracotta clay fired with salt glaze to make them waterproof.
Surely all the ????? that went through sewer pipes would test this salt =
glaze to
its limits? They certainly lasted well. Hope the plastic do as well.
I seem to recall from my discussions with a Mr. Anderson of Eltringham Tile =
and
Pipe Company in 1965 that very little salt actually went inside the pipes =
during
the salting process. Most of the water proofing occurred because of =
bacterial
build up on the inner clay surface. Terra cotta pipes would certainly have =
been
porous and an ideal place for slime to grow. Eltringham used a stoneware =
clay
which was fired to vitrification. Anyway, ninety nine percent of what goes =
down
a sewer is water so any urine or humic acid will be well diluted. Solids may
cause abrasion.
My point was that I had never heard of any analitical work being done nor =
read
comments which related salt glaze composition to current accepted limits for
glaze formulation
Ivor Lewis
Ray Aldridge on tue 9 may 00
At 12:16 AM 5/8/00 EDT, you wrote:
>
>My point was that I had never heard of any analitical work being done nor
read
>comments which related salt glaze composition to current accepted limits for
>glaze formulation
>
It probably hasn't occurred to anyone to do so, because it might be
considered largely pointless, at least insofar as the usual commercial
saltglaze forms are concerned. These are mostly ginger beer bottles,
steins, mustard pots and so forth, and all these forms must be glazed on
the inside with a more conventional glaze, since the salt does a very poor
job of penetrating the interiors of such closed forms. The traditional
slip glazes, such as the Albany slip used inside most old American
saltglazed jugs, are pretty durable. As I recall, that's one reason Albany
slip was favored for those big ceramic insulators formerly used on power
lines.
On the other hand, some artist potters use salt on plates and shallow bowls
and in this case, it would be very interesting to see how stable and
durable the glaze is. I'd tend to think it was pretty durable, since
salt-glazed bellarmines are sometimes exhumed from archaeological sites
after centuries of contact with the soil, and they seem fairly pristine.
By the way, I got the impression that the original poster was asking about
some sort of non-salt orange-peel glaze, though I'm not sure why I thought
that.
Ray
Aldridge Porcelain and Stoneware
http://www.goodpots.com
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