Fara Shimbo on mon 27 may 02
Hi, Folks,
Over many decades of pouring molds I've noticed now and then
that sometimes a white fuzz will form around the pour hole,
and sometimes it will migrate outward from there. Doesn't
happen all the time, but does anybody know what this stuff is,
and what (if anything) it may be doing to my molds? I've
never known it to hurt anything but still...
Hang in there,
Fa
--
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Fara Shimbo, Certified Public Nuisance, Master Crystallier
Shimbo Pottery, Hygiene, Colorado, USA
crystalline-ceramics.info ++ shimbopottery.com
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
"It's great to be known. It's even better to be known
as 'strange.'" -- Kaga Takeshi
Tommy Humphries on mon 27 may 02
Those are calcite crystals.
When the water in your slip is a bit on the acid side (some clays and/or
deflocculants are acid in themselves) some of the calcium from the plaster
will be dissolved. When this water migrates to the lip as the mold dries
the calcium comes out of solution and begins to form crystals. This usually
starts happening on older molds ( or any plaster for that matter). It is
usually a sign that the mold has almost reached the end of its usefullness,
as the calcium migrates to the surface, the plaster will steadily become
weaker.
I have seen old molds that when left out in the weather, will, after drying
in the sun for a couple of days become virtual cotton balls, then with the
next rain the crystals wash off along with a layer of powdery plaster.
Eventually the plaster takes on a very rough texture...almost spiny as
harder areas of the plaster are exposed. Makes for some interesting yard
sculptures.
Tommy
----- Original Message -----
From: "Fara Shimbo"
To:
Sent: Monday, May 27, 2002 11:54 AM
Subject: White Fuzz On Molds?
> Hi, Folks,
>
> Over many decades of pouring molds I've noticed now and then
> that sometimes a white fuzz will form around the pour hole,
> and sometimes it will migrate outward from there. Doesn't
> happen all the time, but does anybody know what this stuff is,
> and what (if anything) it may be doing to my molds? I've
> never known it to hurt anything but still...
>
> Hang in there,
>
> Fa
> --
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> Fara Shimbo, Certified Public Nuisance, Master Crystallier
> Shimbo Pottery, Hygiene, Colorado, USA
> crystalline-ceramics.info ++ shimbopottery.com
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> "It's great to be known. It's even better to be known
> as 'strange.'" -- Kaga Takeshi
>
>
____________________________________________________________________________
__
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>
Michael Banks on tue 28 may 02
If you are using sodium silicate, with or without soda ash, the fuzz is
usually sodium sulphate.
This soluble salt is produced by sodium silicate reacting with the calcium
sulphate mould. Capillary action wicks the resulting solution to the
surface, where evaporation causes the precipitate to form.
Sodium silicate slowly attacks gypsum (plaster) moulds via this process, but
organo-sodium products (dispex, darvan) are much less corrosive.
Michael Banks,
Nelson,
NZ
----- Original Message -----
Fara Shimbo wrote:
> Over many decades of pouring molds I've noticed now and then
> that sometimes a white fuzz will form around the pour hole,
> and sometimes it will migrate outward from there. Doesn't
> happen all the time, but does anybody know what this stuff is,
> and what (if anything) it may be doing to my molds? I've
> never known it to hurt anything but still...
Ceramic Design Group on tue 28 may 02
on 5/28/02 12:10 AM, Michael Banks at mjbanks@CLEAR.NET.NZ wrote:
> If you are using sodium silicate, with or without soda ash, the fuzz is
> usually sodium sulphate.
>
One can eliminate the fuzz altogether by eliminating the use of sodium
silicate/soda ash and substituting Darvan 811. A good place to start is 30ml
Darvan 811 for every 10 pounds of dry materials. 10 pounds dry materials
yields 1 gallon of slip.
Caveat-note that the amount of Darvan 811 may vary for your particular
application and should be tested first before using on a production basis.
Darvan 811 is available from RT Vanderbilt.
Jonathan
Jonathan Kaplan, president
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
voice and fax 970 879-9139
info@ceramicdesigngroup.net
Plant Location:
1280 13th Street Unit 13
Steamboat Springs CO 80487
(please use this address for all deliveries via UPS, comman carrier, Fed Ex,
etc.)
"Custom design and manufacturing for the ceramic arts, giftware and pottery
industries. Molds, models, and tooling for slip casting, jiggering and
hydraulic pressing. Consultation on clay and glaze formulation, production
systems,firing, and kilns.
Tommy Humphries on tue 28 may 02
nope...not necessarily.
I use plaster wedging tables that are kept wet at all times so that super
soft clay will not stick, and often around the perimeter there will grow
this mat of fuzzy crystals, which I probably mistakenly called calcite
instead of gypsum...These wedging tables have never seen any sodium silicate
or any other material except clay and water, so I am sticking to my
story...seems I am not alone it this stand- Hello Dave!
Tommy
----- Original Message -----
From: "Michael Banks"
To:
Sent: Tuesday, May 28, 2002 1:10 AM
Subject: Re: White Fuzz On Molds?
> If you are using sodium silicate, with or without soda ash, the fuzz is
> usually sodium sulphate.
>
> This soluble salt is produced by sodium silicate reacting with the calcium
> sulphate mould. Capillary action wicks the resulting solution to the
> surface, where evaporation causes the precipitate to form.
>
> Sodium silicate slowly attacks gypsum (plaster) moulds via this process,
but
> organo-sodium products (dispex, darvan) are much less corrosive.
>
> Michael Banks,
> Nelson,
> NZ
>
Michael Banks on wed 29 may 02
Hi Dave,
1. If the fuzz is noticeable soluble, (and lieu of a source of sodium) it
can be calcium bicarbonate from "hard water".
2. If the fuzz is only sparing soluble in neutral water, it will most
likely be gypsum derived from the plaster by acidic pore water in the clay.
Natural clays can have quite low pH (from traces of sulphuric and/or humic
acids).
Try testing your clay slurry acidity with pH paper. If too acidic, you could
neutralise it with small additions of lime to protect the plaster slabs.
Michael
in NZ
----- Original Message -----
From: Dave Finkelnburg wrote:
> I accept your explanation, but have a question from it. I observe a
> similar occurrence. The fuzz is really fine crystals of something, a
salt,
> I assume. I get the fuzz growing from the plaster slabs on which I dry
the
> clay slurry made from my clay trimmings and scraps. I do only
wheel-thrown
> or hand built work with commercial clay, and have no sodium silicate,
> Darvan, etc. in my studio. What could the source of the salt be that I am
> observing?
Bobbruch1@AOL.COM on wed 29 may 02
While the white fuzz may be caused by using sodium silicate, it may be that
the way you are casting effects the creation of the white fuzz. I have not
been casting for awhile, but if my memory still functions, I used to get the
white fuzz when I left the slip in the mold for a long time - either to make
an extra thick piece for the purpose of carving or to create a solid piece
to
use as a casting for another mold. This also might occur if I made too many
casts of one mold so that the mold never had a chance to dry out between
casts.
Bob Bruch
<<<<From: Michael Banks
Subject: Re: White Fuzz On Molds?
<<<usually sodium sulphate.
<<<calcium
sulphate mould. Capillary action wicks the resulting solution to the
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