Randall Moody on mon 14 jun 99
I have looked through the archives and found that Barium in terracotta is to
reduce scumming. My question is how much Ba does the job? In one of the
posts L. Arbuckle says that she has found that a maximum of .5% will do the
trick, will less work? Also, I pulled a recipe off the list but do not know
what cone is the max. Here is the recipe:
Red Art 65%
Gold Art 15
Fire Clay 10
Talc 10
Barium a little
John K Dellow on tue 15 jun 99
Before putting BARIUM in your clay body IMHO ,make up a test batch using
distilled water.
From earlier posts on this subject it may be the water used to make up
the body which is causing the addition of soluble salts , which cause
the scumming. Try a test batch with distilled water to rule that out. If
the body still scummes ,then it's one of the clay ingredients causing
scumming .
I would be inclined to try different clays before adding barium into a
body. The old timers who trained me would not use a body with barium
added to it. These potters would be throwing a ton a day and even
exposure to 1/2% would be too much .
Randall Moody wrote:
>
> ----------------------------Original message----------------------------
> I have looked through the archives and found that Barium in terracotta is to
> reduce scumming. My question is how much Ba does the job? In one of the
> posts L. Arbuckle says that she has found that a maximum of .5% will do the
> trick, will less work? Also, I pulled a recipe off the list but do not know
> what cone is the max. Here is the recipe:
>
> Red Art 65%
> Gold Art 15
> Fire Clay 10
> Talc 10
> Barium a little
--
John Dellow "the flower pot man"
ICQ : #2193986 {jacka}
E-mail : dellowjk@kewl.com.au
25 Hugh Guinea Ct, Worongary Q 4213
Ph:+61-7-55302875 Fax:+61-7-55253585
Home Page http://www.welcome.to/jkdellow
Ron Roy on wed 16 jun 99
It is true that the Barium is there to prevent soluble salts from coming to
the surface of clay as it dries. Very noticable on dark clays - still can
be there on lighter clays but is much harder to see. These salts will flux
the clay where they are deposited through evaporation - rims are one place
if the ware is dried upright. This can interfer with glazing in those
areas.
The answer to how much depends on how much soluble salt there is in the
clay to start with - maybe none - in that case the answer is no Barium.
Salts in clays will vary from batch to batch so having some makes good
sense - but idealy just enough to stop the scumming problem - I would start
with less than 0.5 - say 0.2.
The Barium combines with the salts to lock them into the clay - if you have
too much and it does not all combine - some Barium Carb is "left over" - I
don't know if this is a toxicity concern - but leaving slaked clay in an
open bucket - with water on top and cats in the studio might give some
unwanted results.
Perhaps drying terra cotta upside down would be an appropriate technique in
some cases.
RR
>----------------------------Original message----------------------------
>I have looked through the archives and found that Barium in terracotta is to
>reduce scumming. My question is how much Ba does the job? In one of the
>posts L. Arbuckle says that she has found that a maximum of .5% will do the
>trick, will less work? Also, I pulled a recipe off the list but do not know
>what cone is the max. Here is the recipe:
>
>Red Art 65%
>Gold Art 15
>Fire Clay 10
>Talc 10
>Barium a little
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
Pancioli on thu 17 jun 99
Dear Ron:
Soluble salts in a clay body can be a problem if you don't want them.
But once I formulated a series of experiments that encouraged their
development and made a cone 10 body with added solubles that glazed some
embossed tiles very nicely. The solubles evaporated to the high places
on the embossed design, and didn't glaze the low places. (Someone told
me the effect reminded them of a sugar type pastry that does the same
thing.) Adding solubles to the body is the same idea as Egyptian Paste,
but at Cone 10 R the result was much more subtle.
Making lemonade....
Diana
Randall Moody on fri 18 jun 99
Thanks to all who responded about the Ba in terra cotta. Now here is
another question I can't seem to find the answer to in my books. Can you
substitute strontium for barium in a clay body the same as you can in a
glaze? Does it so the same thing for the glaze as it would for the body i.e.
prevent the formation of soluble salts or is it in the glaze for some other
reason?
Thanks!
Randall
Ron Roy on sun 20 jun 99
Hi Randall,
The answer is no - it does not tie up salts like Barium Carb does.
>----------------------------Original message----------------------------
Can you
>substitute strontium for barium in a clay body the same as you can in a
>glaze? Does it so the same thing for the glaze as it would for the body i.e.
>prevent the formation of soluble salts or is it in the glaze for some other
>reason?
>
>Thanks!
>Randall
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
Tom Buck on sun 20 jun 99
Randall Moody:
FYI, the family of alkaline earth elements reads as follows:
Berylium AW (atomic weight) 9; Magnesium 24; Calcium 40; Strontium 87.6;
Barium 137.3; and Radium 226.
The first and the last are toxic and dangerous (radium is also
radioacive). The middle three Mg, Ca, Sr are non-toxic in their common
forms. Barium is toxic in a soluble form (the sulfate is almost
insoluble).
The alkaline earths have atomic structures that make them behave
quite similarly in their chemical activities. So, yes, Strontium
(non-radioactive when it comes from a mine, ie, is "natural") is able to
displace Barium in most uses except those involving physical size of the
atom, eg, in glazes that produce specific colours from other components
("Barium Blue from copper") -- the shape of the BaO vs that of SrO causes
a change in the wavelength of reflected light and therefore the colour our
eyes perceive. So SrO, if used (75 grams SrCO3 = 100 grams BaCO3), will
alter the colour reponse of the same glaze with BaCO3 in it.
But otherwise the non-toxic Strontium Carbonate, in appropriate
particle size range, will be an acceptable alternative to toxic Barium
Carbonate. Tests will be needed to assure yourself that the change is
something you like.
Tom Buck ) tel: 905-389-2339
(westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada
Greg Skwira on wed 23 jun 99
======== Original Message ========
----------------------------Original message----------------------------
Randall Moody:
FYI, the family of alkaline earth elements reads as follows:
Berylium AW (atomic weight) 9; Magnesium 24; Calcium 40; Strontium 87.6;
Barium 137.3; and Radium 226.
The first and the last are toxic and dangerous (radium is also
radioacive). The middle three Mg, Ca, Sr are non-toxic in their common
forms. Barium is toxic in a soluble form (the sulfate is almost
insoluble).
The alkaline earths have atomic structures that make them behave
quite similarly in their chemical activities. So, yes, Strontium
(non-radioactive when it comes from a mine, ie, is "natural") is able to
displace Barium in most uses except those involving physical size of the
atom, eg, in glazes that produce specific colours from other components
("Barium Blue from copper") -- the shape of the BaO vs that of SrO causes
a change in the wavelength of reflected light and therefore the colour our
eyes perceive. So SrO, if used (75 grams SrCO3 = 100 grams BaCO3), will
alter the colour reponse of the same glaze with BaCO3 in it.
But otherwise the non-toxic Strontium Carbonate, in appropriate
particle size range, will be an acceptable alternative to toxic Barium
Carbonate. Tests will be needed to assure yourself that the change is
something you like.
Tom Buck ) tel: 905-389-2339
(westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada
======== Fwd by: Greg Skwira ========
<particle size range, will be an acceptable alternative to toxic Barium
Carbonate.>>
Is that a 1-to-1 replacement, or does an adjustment have to be made?
Thanx.
nina ratrie on thu 24 jun 99
No Randall, you can not substitute strontium carbonate for barium carbonate
in clay bodies to prevent scumming in low fire red clay bodies. As far as I
know barium carbonate is the only thing that you can use in a low fire red
body to prevent scumming.
Nina Ratrie
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