Wood Jeanne on mon 20 oct 03
Greetings,
Some friends who do large banquets several times a
year wrote & asked me a question & I'd like to pass it
on.
They bought several boxes of small bowls from China
from an import store. The bowls were glazed shiny
brown with an unglazed foot rim.
After their last banquet these bowls were washed,
wrapped in bubble wrap and stored in the boxes they
came in, which, in my friends words, were shoddy
boxes. Other pottery was also stored the same way in
the same place.
When they unwrapped the Chinese bowls several months
later they found them covered in mildew the other
pottery (including some of mine) was fine, no mold.
They didn't use the Chinese bowls for this banquet,
instead washed them and wrapped them in new bubble
wrap. But when unwrapped a day later they found a gray
haze covering these bowls.
My friends asked if I knew why, without seeing them I
thought the glaze might be crazed and air bourne mold
spores were able to settle between the tiny crazes.
Possibly also the clay body was underfired and
absorbed water, helping the mold process along.
Any other ideas?
Thanks,
Jeanne W.
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Kristin on tue 21 oct 03
It sounds like you're talking about mold all over the
pot, not just on the bottom. My experience is with
mold just on the unglazed foot, but maybe it relates?
I used to use one of those dreaded "^6 - ^10"
porcelains, firing to ^6. All of these pieces mold on
the bottom when left to air-dry in the dish drainer.
Just slightly, and it's more of a greyish stain that
doesn't really want to wash off than a fuzzy mold.
But mold nonetheless.
I had always assumed that this was a result of the
clay not being done cookin' really, and soaking up
just enough water to sit there and be all organic and
moldy and whatnot.
Maybe?
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Malcolm Schosha on tue 21 oct 03
The pots were probabily not underfired, but certainly were porous. In
the USA many people expect everything to vitrified, particularly now
with microwave ovens (the bowls might have exploded in a microwave).
The bowls just needed time to dry before being wraped in plastic.
Unless the bowls were marked "microwave safe" there was probabily
nothing wrong with the product. They were porous stoneware, or low
fire ceramic. It makes sense to give pottery some time to dry after
washing if they are to be wraped in plastic.
If you are a potter you should know this.
Malcolm Schosha
Brooklyn, NY
--- In clayart@yahoogroups.com, Wood Jeanne wrote:
> Greetings,
> Some friends who do large banquets several times a
> year wrote & asked me a question & I'd like to pass it
> on.
>
> They bought several boxes of small bowls from China
> from an import store. The bowls were glazed shiny
> brown with an unglazed foot rim.
>
> After their last banquet these bowls were washed,
> wrapped in bubble wrap and stored in the boxes they
> came in, which, in my friends words, were shoddy
> boxes. Other pottery was also stored the same way in
> the same place.
>
> When they unwrapped the Chinese bowls several months
> later they found them covered in mildew the other
> pottery (including some of mine) was fine, no mold.
>
> They didn't use the Chinese bowls for this banquet,
> instead washed them and wrapped them in new bubble
> wrap. But when unwrapped a day later they found a gray
> haze covering these bowls.
>
> My friends asked if I knew why, without seeing them I
> thought the glaze might be crazed and air bourne mold
> spores were able to settle between the tiny crazes.
> Possibly also the clay body was underfired and
> absorbed water, helping the mold process along.
>
> Any other ideas?
> Thanks,
> Jeanne W.
>
>
>
> __________________________________
> Do you Yahoo!?
> The New Yahoo! Shopping - with improved product search
> http://shopping.yahoo.com
>
>
______________________________________________________________________
________
> Send postings to clayart@l...
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Ron Roy on thu 23 oct 03
As others have noted - the clay in those pots is not vitrified properly so
they hold water and promote mold growth - especially if wrapped so they
can't dry out.
This will happen with any clay that is not properly vitrified - and take in
all kinds of stuff including oil and sugar - not the best situation for
table ware.
That mold can be killed by leaving the ware in the oven for a while - at
say 200 degrees - store em dry and they will be OK at least till next time.
RR
>Some friends who do large banquets several times a
>year wrote & asked me a question & I'd like to pass it
>on.
>
>They bought several boxes of small bowls from China
>from an import store. The bowls were glazed shiny
>brown with an unglazed foot rim.
>
>After their last banquet these bowls were washed,
>wrapped in bubble wrap and stored in the boxes they
>came in, which, in my friends words, were shoddy
>boxes. Other pottery was also stored the same way in
>the same place.
>
>When they unwrapped the Chinese bowls several months
>later they found them covered in mildew the other
>pottery (including some of mine) was fine, no mold.
>
>They didn't use the Chinese bowls for this banquet,
>instead washed them and wrapped them in new bubble
>wrap. But when unwrapped a day later they found a gray
>haze covering these bowls.
>
>My friends asked if I knew why, without seeing them I
>thought the glaze might be crazed and air bourne mold
>spores were able to settle between the tiny crazes.
>Possibly also the clay body was underfired and
>absorbed water, helping the mold process along.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Malcolm Schosha on thu 23 oct 03
--- In clayart@yahoogroups.com, Ron Roy wrote:
> As others have noted - the clay in those pots is not vitrified
properly so
> they hold water and promote mold growth - especially if wrapped so
they
> can't dry out.
>
> This will happen with any clay that is not properly vitrified - and
take in
> all kinds of stuff including oil and sugar - not the best situation
for
> table ware.
>
> That mold can be killed by leaving the ware in the oven for a
while - at
> say 200 degrees - store em dry and they will be OK at least till
next time.
>
> RR
......................................
Ron,
As you know, even most stoneware will absorb some water. Earthenware,
although "properly" fired, will absorb somewhat more. There is
nothing wrong with that, they just need time to dry.
Since most people now seem to expect vitrified ware for food vessals,
it is best to meet that expectation. However, low-fire vessals have
been used for food many thousands of years, giving good service.
Malcolm Schosha
Brooklyn, NY
Tony Ferguson on thu 23 oct 03
Malcolm,
I would add that unglazed low fire earthenware teapots are noted for their
tannin extraction capabilities with tea. Very prized in Spain.
Thank you.
Tony Ferguson
On Lake Superior, where the sky meets the Lake
Custom & Manufactured Kiln Design
Stoneware, Porcelain, Raku and more
by Coleman, Ferguson, Winchester...
http://www.aquariusartgallery.com
218-727-6339
315 N. Lake Ave
Apt 312
Duluth, MN 55806
----- Original Message -----
From: "Malcolm Schosha"
To:
Sent: Thursday, October 23, 2003 5:24 PM
Subject: Re: Moldy pots
> --- In clayart@yahoogroups.com, Ron Roy wrote:
> > As others have noted - the clay in those pots is not vitrified
> properly so
> > they hold water and promote mold growth - especially if wrapped so
> they
> > can't dry out.
> >
> > This will happen with any clay that is not properly vitrified - and
> take in
> > all kinds of stuff including oil and sugar - not the best situation
> for
> > table ware.
> >
> > That mold can be killed by leaving the ware in the oven for a
> while - at
> > say 200 degrees - store em dry and they will be OK at least till
> next time.
> >
> > RR
> ......................................
>
> Ron,
>
> As you know, even most stoneware will absorb some water. Earthenware,
> although "properly" fired, will absorb somewhat more. There is
> nothing wrong with that, they just need time to dry.
>
> Since most people now seem to expect vitrified ware for food vessals,
> it is best to meet that expectation. However, low-fire vessals have
> been used for food many thousands of years, giving good service.
>
> Malcolm Schosha
> Brooklyn, NY
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>
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