Lynn Goodman Porcelain Pottery on sat 25 mar 06
That white fuzz is soluble salts absorbed from your clay. The plaster
may have only recently absorbed enough from your clay to start growing
the crystals. They are harmless. I have them on my plaster bats--I just
wipe them off before using.
Lynn
On Mar 25, 2006, at 8:04 PM, Dot Burnworth wrote:
> Hey y'all,
> Can someone tell me from whence comes the new white fuzz on my plaster
> wedging tables??? I've had these tables for 2 1/2 years, and just
> about 6 months ago, they started growing white crystal-like
> stuff...mold, I suppose, but very white, clean mold...could it be from
> silica? It grows VERY quickly...seems like overnight there's a bunch
> of it--mostly at the edges near the wood, but sometimes a thin coating
> over the whole surface. What is it doing there, and is it killing me
> slowly??? (or quickly, for that matter?)
> --
> Dot Burnworth
> Woodstock, CT
>
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Lynn Goodman
Fine Porcelain Pottery
548 Court St.
Brooklyn, NY 11231
718-858-6920
Cell 347-526-9805
www.lynngoodmanporcelain.com
Dot Burnworth on sat 25 mar 06
Hey y'all,
Can someone tell me from whence comes the new white fuzz on my plaster
wedging tables??? I've had these tables for 2 1/2 years, and just
about 6 months ago, they started growing white crystal-like
stuff...mold, I suppose, but very white, clean mold...could it be from
silica? It grows VERY quickly...seems like overnight there's a bunch
of it--mostly at the edges near the wood, but sometimes a thin coating
over the whole surface. What is it doing there, and is it killing me
slowly??? (or quickly, for that matter?)
--
Dot Burnworth
Woodstock, CT
Kathy Rhoades on sat 25 mar 06
I get this also. I have a large unglazed terra cotta pot that I will sometimes put my slop in to let it dry. WHen I take it out, I have awhite crystal-like stuff all around the edges of the pot. I thought it might be salts from the water, but I stopped doing it that way until I find out what it is.
Kathy Rhoades from PA
Dot Burnworth wrote:
Hey y'all,
Can someone tell me from whence comes the new white fuzz on my plaster
wedging tables??? I've had these tables for 2 1/2 years, and just
about 6 months ago, they started growing white crystal-like
stuff...mold, I suppose, but very white, clean mold...could it be from
silica? It grows VERY quickly...seems like overnight there's a bunch
of it--mostly at the edges near the wood, but sometimes a thin coating
over the whole surface. What is it doing there, and is it killing me
slowly??? (or quickly, for that matter?)
--
Dot Burnworth
Woodstock, CT
______________________________________________________________________________
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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Snail Scott on sun 26 mar 06
At 08:04 PM 3/25/2006 -0500, you wrote:
>Hey y'all,
>Can someone tell me from whence comes the new white fuzz on my plaster
>wedging tables??? I've had these tables for 2 1/2 years, and just
>about 6 months ago, they started growing white crystal-like
>stuff...
Those are salt crystals - kinda cool to look at,
now that you know they won't kill you, huh?
They are common on slip-casting molds because of
salty deflocculants, though rarer on 'regular'
clay surfaces. Since a wedging table absorbs less
water than a mold, it will take longer for the
salt saturation to reach a point where the salts
are fourced up and out to form crystals whe the
plaster dries each time.
Either the local water you use for claymaking has
a high mineral content, or a component of your clay
body has a fair amount of soluble salts. (Some
clays have more than others.) These salts in clay
(whether from clay itself or the water) are the
same ones that cause the 'scumming' effect on
earthenware.
Just brush off the crystals and wedge away!
Or start a science project...
-Snail
j e motzkin on sun 26 mar 06
Dot, the white crystal fuzz is the efflorescence of soluble salts.
You can scrape it off and proceed to use the plaster.
Judy
From: Dot Burnworth
Subject: white fuzz on my plaster!
Hey y'all,
Can someone tell me from whence comes the new white fuzz
on my plaster
wedging tables??? I've had these tables for 2 1/2 years,
and just
about 6 months ago, they started growing white
crystal-like
stuff.
/motzkin/studio/7 TUFTS Street/Cambridge, MA 02139/
617-547-5513/jmotzkin@yahoo.com/
http://www.motzkin.com/
http://spiritkeeper-urns.com
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Ivor and Olive Lewis on mon 27 mar 06
Dear Dot Burnworth,=20
First of all you need to find out if this growth is organic or =
inorganic. Collect some and put it on the end of a metal spatula. Heat =
it to red heat. If it burns away it is organic. If you still have a =
white residue you have inorganic and it will cause you no harm from =
infectious disease.
But since you say it is crystalline then it may just be Calcium Sulphate =
migrating to the surface of you plaster. Plaster is Calcium Sulphate. =
There are three forms Fully hydrated , Semi-hydrated and Anhydrous. =
Potters plaster is Anhydrous, or nearly so. When water is added to it =
some dissolves in the water, undergoes a chemical reaction and the new =
chemical is insoluble. This is what binds plater into a solid mass.
When you work clay on a plaster block, or de-water clay slurry the =
adsorbed water dissolves some of the plaster. This solution migrates to =
the surface where it dries and leaves the residue you are seeing.
There may be a beneficial incidental effect of the Gypsum/Water =
interaction. If clay is being kneaded or wedged on a plaster surface it =
will begin to react with the Calcium sulphate solution, or perhaps water =
in the clay may begin to dissolve the surface of the plaster. Since =
Kaolin and Ball Clay act as Ion Exchange Media, small strongly charged =
Calcium ions can displace large weakly charged ions from clay surfaces. =
This seems to give Clay a better hold on water. I believe the effect is =
to increase the plastic strength of a clay, making it firmer and helping =
it to be thrown to greater elevations, extended to greater diameters or =
drawn to thinner sections.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Tom Buck on tue 28 mar 06
DotB:
Chances are high that the white fuzz is calcium carbonate
(limestone/whiting). dry (new) plaster is calcium sulfate
hemi-(mono)hyrdate (H2O) which forms calcium sulfate duohydrate (2H2O) aka
"gypsum" when mixed with water and allowed to "set".
when you put clay slip in a plaster form, the pores of the plaster
suck out the water from the clay, allowing it to set-up. then when you
remove the clay form, and allow the "mold" to dry out, water from inside
the plaster comes to the surface, taking with the water Calcium ions
(Ca++) and this liquid reacts with Carbon Dioxide from the air to form
insoluble Calcium Carbonate ("fuzz").
this reaction occurs repeatedly and it the main reason plaster
forms become useless after a set number of castings (the surface
eventually gets coated with a layer of limestone and this blocks water
take-up from clayslip). sometimes, sanding the surface to remove the
limestone will rejuvenate a plaster form.
good pots. peace Tom B.
Tom Buck ) -- primary address.
"alias" or secondary address.
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street, Hamilton ON L8T 3E1 Canada
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