Bob Stryker on wed 26 aug 98
Dear Group,
I have a customer who is using a Minnesota Clay glaze over another
manufacturer's clay body. The bisqued clay (tiles) are showing areas
that appear similar to scumming that I have seen on cast ware. The
glaze is pitting and sometimes crawling over the areas where the
scumming patches are.
Does anyone have a recommendation for a strategy that this customer can
use to try to salvage a large number of already bisqued tiles that have
scumming on them? Most of the references I have only mention how to
avoid scumming by the addition of barium carbonate to the clay recipe,
none mention how it may be dealt with in the fired state.
Thanks in advance.
Bob Stryker
Minnesota Clay USA
http://www.mm.com/mnclayus/
Tony Hansen on mon 31 aug 98
>Does anyone have a recommendation for a strategy that this customer can
>use to try to salvage a large number of already bisqued tiles that have
>scumming on them? Most of the references I have only mention how to
>avoid scumming by the addition of barium carbonate to the clay recipe,
>none mention how it may be dealt with in the fired state.
You should be able to get some sort of acid from a brick supply store.
Brick layers use it to remove effluorescence from brick walls.
--
T o n y H a n s e n thansen@digitalfire.com
Don't fight the dragon alone http://digitalfire.com
Calculation/Database Software for Ceramic Industry
John K. Dellow on tue 1 sep 98
Tony ,
Here in australia brick layers use a white oil ,usually canola, to clean
off the scum on bricks. Have passed this on to Bob. Acid doesn't work as
well. Have heard of bricky`s using sump oil also, a bit messy :).
John Dellow the flower pot man
Hudson Mackenzie on mon 14 may 01
from Bill Miller (billmill3@worldnet.att.net) via hudson@potters.org
I've been getting white powdery looking deposit in areas on sculpture usi=
ng, "red clay #104 with grog" by Standard Ceramic Supply of Pittsburgh. =
Firing was to cone 04 in an electric kiln. Any recommendations?
Rod, Marian, and Holly Morris on tue 15 may 01
I queried this a while back, since I also work in terra cotta. Someone
suggested oiling the surface with light oil, like salad oil,as a cosmetic
solution. (I was afraid of the barium). It worked out OK on light scumming.
New question: what about barium sulfate instead of carbonate. Barium sulfate
is inert, as I understand it, but maybe it's sulfate because it has already
chemically bonded with sulfates, and hence won't bond with the nasty
sulfates in the clay. Just wondering.
Marian in Michigan
----- Original Message -----
From: "mudlark"
To:
Sent: Tuesday, May 15, 2001 11:47 AM
Subject: Re: scumming
> Barium Carb. is most common as the solution. Renders the salts insoluble.
Laguna uses .5% I use .2% I can depend on the clays. It is usually mixed in
to begin with in the batch. Wear Rubber gloves if you wedge it
> in. Or strontiun carb works and is'nt toxic. I would put it on my cereal
though.
>
> Hudson Mackenzie wrote:
>
> > from Bill Miller (billmill3@worldnet.att.net) via hudson@potters.org
> >
> > I've been getting white powdery looking deposit in areas on sculpture
using, "red clay #104 with grog" by Standard Ceramic Supply of Pittsburgh.
Firing was to cone 04 in an electric kiln. Any recommendations?
> >
> >
mudlark on tue 15 may 01
Barium Carb. is most common as the solution. Renders the salts insoluble.=
Laguna uses .5% I use .2% I can depend on the clays. It is usually mixed=
in to begin with in the batch. Wear Rubber gloves if you wedge it
in. Or strontiun carb works and is'nt toxic. I would put it on my cereal =
though.
Hudson Mackenzie wrote:
> from Bill Miller (billmill3@worldnet.att.net) via hudson@potters.org
>
> I've been getting white powdery looking deposit in areas on sculpture u=
sing, "red clay #104 with grog" by Standard Ceramic Supply of Pittsburgh.=
Firing was to cone 04 in an electric kiln. Any recommendations?
>
> _______________________________________________________________________=
_______
> 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@pcl=
ink.com.
--
Clyde Tullis
Mudlark Pottery
320 G Street
Salida, CO 81201
719-539-1299
mudlark@chaffee.net
http://www.mudlarkpottery.com
Snail Scott on tue 15 may 01
At 08:01 PM 5/14/01 -0400, you wrote:
> from Bill Miller (billmill3@worldnet.att.net) via hudson@potters.org
>
>I've been getting white powdery looking deposit in areas on sculpture
using, "red clay #104 with grog" by Standard Ceramic Supply of Pittsburgh=
=2E
Firing was to cone 04 in an electric kiln. Any recommendations?
Earthenware clays are often subject to
surface scumming - it's the soluble salts
rising to the surface. Many manufacturers
add barium to inhibit this. (Tiny amounts;
don't freak out!) Also, the longer the
piece takes to dry, the more time the salts
have to migrate. (I once made a piece from
clay that normally doesn't scum much; I
kept it wrapped and damp for six months,
while the commission details were in limbo.
When I finally resumed work, it looked
furry with salts!) Clean them off when
possible; they often affect the final fired
surface especially if the clay is left bare.
(It can even affect stoneware visibly.)
1. Use a barium-containing clay.
2. Dry it as quickly as possible.
-Snail
Steve Mills on wed 16 may 01
This is a problem which sometimes affects (in particular) red clays over
here in the UK. It is not a continuous problem as it seems to be
dependant on local condition in the clay seams. The only cure that we
are aware of (which many will baulk at) is the addition of a very small
amount of Barium Carbonate to the body, about 2 percent. The scumming is
brought about by handling the plastic clay (but doesn't seem to prevail
when throwing) and is apparently a reaction to something on the makers
hands causing salts to migrate to the surface. My cure, on the occasions
when it happened, was to wear disposable plastic gloves!
Steve
Bath
UK
In message , Hudson Mackenzie writes
> from Bill Miller (billmill3@worldnet.att.net) via hudson@potters.org
>
>I've been getting white powdery looking deposit in areas on sculpture usi=
>ng, "red clay #104 with grog" by Standard Ceramic Supply of Pittsburgh. =
>Firing was to cone 04 in an electric kiln. Any recommendations?
--
Steve Mills
Bath
UK
Matt MacIntire on wed 16 may 01
Mudlark wrote:
>> Barium Carb. is most common as the solution. Renders the salts insoluble.
Laguna uses .5% I use .2% I can depend on the clays.
Say it ain't so... Laguna adds BARIUM CARBONATE into their clay bodies?!!
Sure it might work. But why would anyone add something so toxic to
something so harmless...?
Some folks may worry about fumes from a salt kiln or should they wear a dust
mask in the studio. These are nothing compared to the danger that Barium
Carbonate poses. As I recall, a lethal dose of Barium Carb is astoundingly
low. I would NEVER add it to my clay. I think it is irresponsible to
advise someone to add it to their clay unless they are fully aware of the
danger it poses, as I expect your are.
But... your mileage may vary.
It is also my understanding that Strontium Carbonate is also toxic, just not
quite as toxic as Barium Carbonate. I expect others here will correct me if
I am in error...
Matt
-----Original Message-----
From: mudlark [mailto:mudlark@CHAFFEE.NET]
Sent: Tuesday, May 15, 2001 11:48 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: scumming
It is usually mixed in to begin with in the batch. Wear Rubber gloves if you
wedge it
in. Or strontiun carb works and is'nt toxic. I would put it on my cereal
though.
Hudson Mackenzie wrote:
> from Bill Miller (billmill3@worldnet.att.net) via hudson@potters.org
>
> I've been getting white powdery looking deposit in areas on sculpture
using, "red clay #104 with grog" by Standard Ceramic Supply of Pittsburgh.
Firing was to cone 04 in an electric kiln. Any recommendations?
>
>
____________________________________________________________________________
__
> 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.
--
Clyde Tullis
Mudlark Pottery
320 G Street
Salida, CO 81201
719-539-1299
mudlark@chaffee.net
http://www.mudlarkpottery.com
____________________________________________________________________________
__
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.
Matt MacIntire on wed 16 may 01
OK, I may have overreacted a bit. My memory served me poorly. A bit of
research (that I should have done first) and I see that several sources
indicate that Strontium has "low toxicity." I stand corrected about
Strontium Carb. I apologize for posting an inaccurate statement. There is
already enough unnecessary alarm about our materials.
What I may have been remembering is that there is sometimes (normal)
contamination of Strontium Carbonate with Barium Carbonate. I saw a MSDS
(link below) that indicates Strontium Carbonate may contain Barium Carbonate
in amounts of 0.4 - 1.5% It is this Barium content that makes me suspicious
of Strontium Carbonate.
Here is a MSDS for Strontium Carbonate
http://www.hummelcroton.com/m_srco3.html
I also did see that Barium Carb can be used to neutralize sulfates in clay
bodies. Mudlark was quite correct on that recommendation.
However, I still think that this is a cure that is worse than the disease.
I'd prefer not to have Barium Carbonate in my clay - or in my studio. I
respect that others' needs are surely different.
When I worked in a ceramic supply warehouse, I handled all these glaze
materials daily. The only compound that I came to fear was Barium
Carbonate. I hated bagging up orders of Barium. I may at times forget the
details, but I remember the avoidance... It may cloud my judgment.
Now here is a special section for web heads... When looking for toxicity
info, I saw a bizarre article about Barium Poisoning. Mentions several
aspects of Barium toxicity. How they can use Barium Sulfate for X-rays.
How Barium Sulfate (less soluble that carbonate) was used to make a rind on
Gorgonzola cheese. Has a bizarre story about someone who used flour
containing 23% Barium Carb. to make some noodles... Fairly interesting
reading...
http://members.tripod.com/~Prof_Anil_Aggrawal/POISO016.HTML
Can we trust what we read on the web...?
Returning now to our regular programming...
Matt
-----Original Message-----
From: mudlark [mailto:mudlark@CHAFFEE.NET]
Sent: Tuesday, May 15, 2001 11:48 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: scumming
Barium Carb. is most common as the solution. Renders the salts insoluble.
Laguna uses .5% I use .2% I can depend on the clays. It is usually mixed in
to begin with in the batch. Wear Rubber gloves if you wedge it in. Or
strontiun carb works and is'nt toxic. I would put it on my cereal though.
Hudson Mackenzie wrote:
> from Bill Miller (billmill3@worldnet.att.net) via hudson@potters.org
>
> I've been getting white powdery looking deposit in areas on sculpture
> using, "red clay #104 with grog" by Standard Ceramic Supply of
> Pittsburgh. Firing was to cone 04 in an electric kiln. Any
> recommendations?
>
> ______________________________________________________________________
> ________
> 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.
--
Clyde Tullis
Mudlark Pottery
320 G Street
Salida, CO 81201
719-539-1299
mudlark@chaffee.net
http://www.mudlarkpottery.com
____________________________________________________________________________
__
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.
Marek & Pauline Drzazga-Donaldson on wed 16 may 01
Additions of 0.1% Barium Carbonate are often used, but the best way I =
have found is to fire the clay higher, this has always got rid of =
scumming.
happy potting Marek http://www.moley.uk.com
Tom Buck on wed 16 may 01
The Morrises & Mudlark:
There is some chemistry involved in curing scumming, and somehow
you are ovelooking it.
If you or your supplier obtain dug-clay and use it "untreated"
then you may well encounter scumming. It arises from materials attached to
the alumino-silicate clay particles by adsorption, that is, weak forces
attracting molecules of soluble salts to the surface of the clay
particles. As the clay (now a pot) dries, the adsorbed salts (as ions)
leave the surface of the clay particles and become dissolved in the water
(of lubrication). The solution migrates to the surface of the pot and the
salts become deposited on the pot's surface once the water evaporates.
When the pot is bisque-fired, the surface salts, largely sulfates of
calcium and magnesium, become oxides and show up as white scum firmly
attached to the claybody's surface.
Makers of claybodies add Barium Carbonate, up to 1%, to overcome
this effect of natural clays. BaCO3, in part, dissolves in the water of
lubrication, and the Ba++ ions seek out SO4-- ions adsorbed on the clay
particles, and two combine to form highly insoluble BaSO4 molecules; these
stay where formed, so the water goes to the surface with little or no
solubles. Hence no scum on firing.
BTW, Mudlark, Strontium Carbonate will NOT bind SO4-- ions because
the SrSO4 is too soluble; the Sr++ ions and SO4-- ions still get to the
surface and form scum on firing.
good pots. bfn. peace. tom b.
Tom Buck ) tel: 905-389-2339
(westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada
Snail Scott on wed 16 may 01
At 10:18 AM 5/16/01 +0100, you wrote:
The scumming is
>brought about by handling the plastic clay (but doesn't seem to prevail
>when throwing) and is apparently a reaction to something on the makers
>hands causing salts to migrate to the surface.
>Steve
I don't believe it's handbuilding that causes
scumming. As I said in my previous post, the
more time the clay spends wet, the more time
the salts have to rise to the surface. (Sort
of like the Egyptian paste effect, scaled down.)
People who throw tend to finish their pieces
quickly, and begin drying them immediately.
They're often ready for firing within the week.
Handbuilders may spend a whole week (or more)
on a single piece, before drying it more slowly
to reduce the stress on an irregular form.
This gives much more time for the salts to
migrate.
Working/drying time, NOT technique per se, is
the contributing factor.
-Snail
Susan Fox Hirschmann on wed 16 may 01
I am also having the same problem with figurative sculpture using Campbell's
^04-^06 earthenware. If campbell is out there listening, what gives here?
Any other solutions out there besides the oil (<<the sculpture?)
susan
annandale, va
Jonathan Kaplan on wed 16 may 01
All high iron bearing clays such as REd Art, Newman Red, Imco Red, etc...
contain materials that are soluble salts and will migrate to the surface and
cause discoloration in the bisque ware which could impact your glazes. Low
grade shale clays are also susceptible to scumming
A small amount, read, SMALL, like one half of one percent is usually enough
to neutralize this annoying defect.
If you are using clay in the box, ask your clay supplier if they put a small
amount of barium carbonate in their mixture. You can't add barium carb to an
already existing pugged/mixed plastic batch.
If you are mixing your own clay, dissolve the amount of barium in water
FIRST, sieve it, and then add the dry clays to this mixture.
Jonathan
--
Jonathan Kaplan
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
infor@ceramicdesigngroup.net www.ceramicdesigngroup.net
(use PO BOX for all USPS correspondence)
Plant Location
1280 13th Street
Steamboat Springs CO 80487
(use PLANT LOCATION for all UPS, Common Carrier, and Courier deliveries)
Veena Raghavan on wed 16 may 01
> the best way I have found is to fire the clay higher, this has always got
rid of scumming<
Marek's advice to fire higher is a new one I have not previously seen on
Clayart or anywhere else. Sounds interesting. Tom Buck suggested a slow
bisque to minimise salts surfacing.
What I have tried is John Dellow's advice of removing the scum by rubbing
on canola oil. I found this worked very well, and the scum did not come
back. I did not put on an excess of canola, so the pots were not oily.
Thanks again, John, for your tip that has worked well for me!
Veena
Veena Raghavan
75124.2520@compuserve.com
mudlark on wed 16 may 01
I stand corrected onthe use of Strontium Carb. for scumming. The Science makes
sense. I remember testing it many years ago and thought it worked. Oh well.
I emailed Laguna about Barium and they felt, as I do, that there isn't enough to
worry about. I no longer lick instead of slip though.
I've experienced this problem with all clays except may be porcelain. It's
terrible on raku and if you leave unglazed areas on terracotta it's pretty ugly.
Matt MacIntire wrote:
> OK, I may have overreacted a bit. My memory served me poorly. A bit of
> research (that I should have done first) and I see that several sources
> indicate that Strontium has "low toxicity." I stand corrected about
> Strontium Carb. I apologize for posting an inaccurate statement. There is
> already enough unnecessary alarm about our materials.
>
> What I may have been remembering is that there is sometimes (normal)
> contamination of Strontium Carbonate with Barium Carbonate. I saw a MSDS
> (link below) that indicates Strontium Carbonate may contain Barium Carbonate
> in amounts of 0.4 - 1.5% It is this Barium content that makes me suspicious
> of Strontium Carbonate.
>
> Here is a MSDS for Strontium Carbonate
> http://www.hummelcroton.com/m_srco3.html
>
> I also did see that Barium Carb can be used to neutralize sulfates in clay
> bodies. Mudlark was quite correct on that recommendation.
>
> However, I still think that this is a cure that is worse than the disease.
> I'd prefer not to have Barium Carbonate in my clay - or in my studio. I
> respect that others' needs are surely different.
>
> When I worked in a ceramic supply warehouse, I handled all these glaze
> materials daily. The only compound that I came to fear was Barium
> Carbonate. I hated bagging up orders of Barium. I may at times forget the
> details, but I remember the avoidance... It may cloud my judgment.
>
> Now here is a special section for web heads... When looking for toxicity
> info, I saw a bizarre article about Barium Poisoning. Mentions several
> aspects of Barium toxicity. How they can use Barium Sulfate for X-rays.
> How Barium Sulfate (less soluble that carbonate) was used to make a rind on
> Gorgonzola cheese. Has a bizarre story about someone who used flour
> containing 23% Barium Carb. to make some noodles... Fairly interesting
> reading...
> http://members.tripod.com/~Prof_Anil_Aggrawal/POISO016.HTML
>
> Can we trust what we read on the web...?
>
> Returning now to our regular programming...
>
> Matt
>
> -----Original Message-----
> From: mudlark [mailto:mudlark@CHAFFEE.NET]
> Sent: Tuesday, May 15, 2001 11:48 AM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: scumming
>
> Barium Carb. is most common as the solution. Renders the salts insoluble.
> Laguna uses .5% I use .2% I can depend on the clays. It is usually mixed in
> to begin with in the batch. Wear Rubber gloves if you wedge it in. Or
> strontiun carb works and is'nt toxic. I would put it on my cereal though.
>
> Hudson Mackenzie wrote:
>
> > from Bill Miller (billmill3@worldnet.att.net) via hudson@potters.org
> >
> > I've been getting white powdery looking deposit in areas on sculpture
> > using, "red clay #104 with grog" by Standard Ceramic Supply of
> > Pittsburgh. Firing was to cone 04 in an electric kiln. Any
> > recommendations?
> >
> > ______________________________________________________________________
> > ________
> > 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.
>
> --
> Clyde Tullis
> Mudlark Pottery
> 320 G Street
> Salida, CO 81201
> 719-539-1299
> mudlark@chaffee.net
> http://www.mudlarkpottery.com
>
> ____________________________________________________________________________
> __
> 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.
>
> ______________________________________________________________________________
> 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.
--
Clyde Tullis
Mudlark Pottery
320 G Street
Salida, CO 81201
719-539-1299
mudlark@chaffee.net
http://www.mudlarkpottery.com
Snail Scott on wed 16 may 01
At 07:55 PM 5/16/01 -0400, you wrote:
>> the best way I have found is to fire the clay higher, this has always got
>rid of scumming<
>
>Marek's advice to fire higher is a new one I have not previously seen on
>Clayart or anywhere else. Sounds interesting. Tom Buck suggested a slow
>bisque to minimise salts surfacing.
Doesn't work for me. I have ^6 stoneware pieces that
had scumming only on parts (due to uneven wrapping
of plastic when drying. I thought it would fire out,
but the scummed areas turned darker in the reduction
firing. (acting as a flux, maybe?)
-Snail
Earl Brunner on thu 17 may 01
This can be a problem even with high fire clays. A while back we were
experimenting with ways to dry large (20 or more inches) platters slowly
and evenly. One potter came up with this great idea to punch pencil
size holes in plastic about an inch apart so that there was a more or
less even distribution of holes for moisture to get out.
The soluble salts in the clay migrated and deposited them selves in neat
little circles all over the platters and fluxed when fired. Made for an
"interesting" look...
Snail Scott wrote:
> At 07:55 PM 5/16/01 -0400, you wrote:
>
>>> the best way I have found is to fire the clay higher, this has always got
>>
>> rid of scumming<
>>
>> Marek's advice to fire higher is a new one I have not previously seen on
>> Clayart or anywhere else. Sounds interesting. Tom Buck suggested a slow
>> bisque to minimise salts surfacing.
>
>
>
> Doesn't work for me. I have ^6 stoneware pieces that
> had scumming only on parts (due to uneven wrapping
> of plastic when drying. I thought it would fire out,
> but the scummed areas turned darker in the reduction
> firing. (acting as a flux, maybe?)
>
> -Snail
>
> ______________________________________________________________________________
> 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.
--
Earl Brunner
http://coyote.accessnv.com/bruec
mailto:bruec@anv.net
Marek & Pauline Drzazga-Donaldson on fri 18 may 01
Dear Earl,
not so much about scumming but more with evenness of drying large =
platters (I throw 30" - 40" platters from time to time) and the like. I =
wrap everything in newspaper (don't get scumming), sometimes dampened if =
the article has some drier parts, and then in bin liner plastic - the =
newspaper evens out the transfer of water (don't ask me how) and gives =
me very good results. Sometimes the print stays on the piece after =
bisque firing - but has never so far caused any scumming or marking with =
the clays I use.
Happy potting Marek http://www.moley.uk.com=20
Stephani Stephenson on fri 18 may 01
Years back , one of our school clay bodies was prone to scumming. I
often made unglazed combination vessel/figurative work and the head and
face of the figure was usually at the top of the piece
Evaporating water left there last and so that is where the salts
were deposited , causing scumming right on the facial/ focal area.
Firing higher just cause that area to flux. (i.e. faces with green
noses and the like !) Rarely did it 'add to the piece!'
At that time I adapted by simply drying pieces bottom or side up, so
that scumming or fluxing would occur on part of the piece where it was
inconsequential or assimilated into other surface treatment .
Stephani
Russel Fouts on fri 1 jun 01
Earl,
>> This can be a problem even with high fire clays. A while back we were
experimenting with ways to dry large (20 or more inches) platters slowly
and evenly. One potter came up with this great idea to punch pencil size
holes in plastic about an inch apart so that there was a more or less even
distribution of holes for moisture to get out. The soluble salts in the clay
migrated and deposited them selves in neat little circles all over the
platters and fluxed when fired. Made for an "interesting" look... <<
I have a white bisque slip made from the waste from my white terra-sig.
Takes a LOT of epsom salts to suspend it. When I decorate my plates with a
spiral pattern, the salts bleed through to the other side an make a nice
echo of the interior spiral on the back.
Russel
Russel Fouts
Mes Potes & Mes Pots
Brussels, Belgium
Tel: +32 2 223 02 75
Mobile: +32 476 55 38 75
Http://www.mypots.com
http://www.Japan-Net.ne.jp/~iwcat
Ron Roy on mon 4 jun 01
Make that - all clays are capable of arriving with salts in them. You see
the salts on the surface of the darker clay even in oxidation - if you test
raw clays in reduction you will see them on most clays at one time or
another.
Even the Kaolins come with salts sometimes - all the ball clays and even
the fire clays.
The reason for the sentence below - salts are more easily seen on dark clays.
RR
>All high iron bearing clays such as REd Art, Newman Red, Imco Red, etc...
>contain materials that are soluble salts and will migrate to the surface and
>cause discoloration in the bisque ware which could impact your glazes. Low
>grade shale clays are also susceptible to scumming
>
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
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