Gibson/Green on wed 24 feb 99
I am casting vases with a commercial c/4-6 casting slip. I'm having a =
problem
with water-tightness. I place the fired pieces on a piece of newsprint and =
fill
them about halfway with water and wait. After about 3 hours a couple of the
vases show condensation (slight buckling of the paper underneath). Left
overnight about a third of the pots show either the same condensation or an
actual slight spot of wetness. The rest show no moisture at all.
I'm using a high-gloss glaze inside (which doesn't appear to be crazing) and
either a gloss or matt outside. Is it possible that a small flaw or pinhole=
on
the inside can allow moisture to enter the body and sweat through the base?
I've been told that even without a glaze this casting body should be
water-tight=21
....and then, is a vase with a slight amount of condensation at the base
acceptable to put on the market?
Your comments would really be appreciated --
Leslie Green
gibgrn=40peak.org
Marcia Kindlmann on thu 25 feb 99
Subject: Sweaty Vases at c/6
Hi Leslie,
Is it possilbe that you're talking about vases _seeping_ rather than
getting condensation? Condensation is what happens when you take a
pitcher of orange juice or a bottle of wine out of the refrig. on a hot
day and water droplets begin to appear all over the outside -- this is
water from the ambient air. People usually expect this to happen,
taking something from refrig. to room temp., so they put the container
on a coaster or mat or whatever if they have a nice wooden table.
When you put a vase on some newspaper and the next day (or sooner)
there's moisture on the paper, in the absence of condensation, that's
seeping. People do not usually expect vases to seep.
It's hard to understand why a vase glazed on the inside should seep.
But some do. I'm trusting that we'll hear from more technical minds on
this.
My thoughts about putting seepers on the market --- it's the kind of
thing that makes people suspicious about buying pottery - anybody's
pottery. Sure, to be honest you can tell the customer that this vase
will seep, but maybe after awhile they forget and give it to somebody,
etc...... just better not to risk losing people's good will.
Marcia in Guilford CT
Brian Crocker on sat 27 feb 99
G'day Leslie,
I would'nt sell a pot that leaks ,, eventualy the problem will come home to you.
I was managing a Pottery some time ago and we had the same problem,, they were
Wine Bottles, we filled the samples from the batch with water coloured with a
Green vegetable die, they showed a colour on white paper after 3 days and we
said the Port wine must be thicker than water so it's OK.
Off went two truck loads 500 miles away. A call came 10 days later " I think
you should see your bottles they are on the shelf in the show room growing Port
Stalactites ,, it looks nice but I cant sell them.
It cost us heaps to empty the Port Wine and refire them to 2 cones higher they
Vitrified and all was OK.
So all I can say is put them back in the kiln and go a few cones higher, or
test
several and find just how high you have to go without having a molten glob
on the kiln shelf, then find a glaze that matches and seals. Never but never
send out leakers.
All the best and Kind regards Brian C.,
At 08:29 PM2:10: 24/02/99 EST, you wrote:
>----------------------------Original message----------------------------
>
>I am casting vases with a commercial c/4-6 casting slip. I'm having a problem
>with water-tightness. I place the fired pieces on a piece of newsprint and
fill
>them about halfway with water and wait. After about 3 hours a couple of the
>vases show condensation (slight buckling of the paper underneath). Left
>overnight about a third of the pots show either the same condensation or an
>actual slight spot of wetness. The rest show no moisture at all.
>
>I'm using a high-gloss glaze inside (which doesn't appear to be crazing) and
>either a gloss or matt outside. Is it possible that a small flaw or pinhole on
>the inside can allow moisture to enter the body and sweat through the base?
>I've been told that even without a glaze this casting body should be
>water-tight!
>
>...and then, is a vase with a slight amount of condensation at the base
>acceptable to put on the market?
>
>Your comments would really be appreciated --
>
>Leslie Green
>gibgrn@peak.org
>
>
Brian Crocker
4 Erica Street,
Tea Tree Gully 5091,
South Australia,
Australia. {e.mail} crocker@dove.com.au
" When a Potter Gives or Sells Pots. Part of a Life is Given Also " CR
OC.
Ron Roy on sat 27 feb 99
Hi Leslie,
You do not say what cone you are firing to - if you are not using cones in
the kiln with the pots you don't know what temp you are reaching. How long
is your firing - particulaly during the last half of it?
Sounds like the clay is not properly vitrified - if you want to test for
that I will tell you how.
Even if the glaze is crazed - if the clay is fired high enough the water
should not get through.
No! don't sell vases that let water through - at least waterproof them - I
have heard that white glue and water will do the trick but don't know what
concentration works - perhaps others can recommend what and how to do it.
RR
>----------------------------Original message----------------------------
>
>I am casting vases with a commercial c/4-6 casting slip. I'm having a problem
>with water-tightness. I place the fired pieces on a piece of newsprint
>and fill
>them about halfway with water and wait. After about 3 hours a couple of the
>vases show condensation (slight buckling of the paper underneath). Left
>overnight about a third of the pots show either the same condensation or an
>actual slight spot of wetness. The rest show no moisture at all.
>
>I'm using a high-gloss glaze inside (which doesn't appear to be crazing) and
>either a gloss or matt outside. Is it possible that a small flaw or pinhole on
>the inside can allow moisture to enter the body and sweat through the base?
>I've been told that even without a glaze this casting body should be
>water-tight!
>
>...and then, is a vase with a slight amount of condensation at the base
>acceptable to put on the market?
>
>Your comments would really be appreciated --
>
>Leslie Green
>gibgrn@peak.org
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
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