lili krakowski on tue 10 feb 04
Taylor wondered why how come whiting and Wollastonite in same recipe. =
He might have asked as well why Talc and Dolomite, Clay and Pyrophylite =
and about other duets of ingredients.
Whiting is Calcium Carbonate and shrinks a lot.
Wollastonite is calcium and silica and shrinks far less.
Dolomite is calcium and magnesium ans shrinks a lot.
Talc is magnesium and silica and shrinks far less.
Pyrophylite shrinks less than clay. =20
So. C'est tr=E8s possible that:
The original recipe with Wollastonite needed more flux- whiting added.
It is possible that the original recipe called for ALL whiting and =
crazed and Wollastonite was used to replace whiting and cure crazing.
It is possible that YOUR recipe is the result of a straight line or =
triaxial blend and the originator did not feel like recalculating.
And sometimes for reasons I do not know replacing an ingredient with the =
"same" from another source gives a nicer effect. Or why molecular =
formulae are not the perfect answer....
Lili Krakowski
Be of good courage
Ababi Sharon on thu 12 feb 04
Yes Lily is correct
however I look at it a bit different.
In a given recipe I have a given amount of CaO and a given amount of MgO
I know I better use Wollastonite than the whiting because I read Tony
Hansen's articles and read RR letters to clayart that tell me: Why
bother with the LOI of the whiting? Buy one and have two: (Wollastonite!
CaO+SiO2)
When it comes to the MgO unless you look for a crawling glaze you look
around: Where can I hide the MgO - Oh dear I have found talc great I
have enough silica what next? Dolomite Oh I have enough CaO what now?
Magnesium carbonate!
This might explain you why there are recipes with many variations of
each oxide.
(This story is copyrighted you may copy it and feel guilty!)
=20
Ababi Sharon
Glaze addict
Kibbutz Shoval Israel
ababisha@shoval.org.il
http://ababi.active.co.il
http://www.matrix2000.co.nz/Matrix%20Demo/Ababi.htm
To Ceramics forum in Hebrew:
http://www.botzpottery.co.il/kishurim.html=20
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of lili
krakowski
Sent: Wednesday, February 11, 2004 3:57 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Whiting and Wollastonite/ Dolomite and Talc
Taylor wondered why how come whiting and Wollastonite in same recipe.
He might have asked as well why Talc and Dolomite, Clay and Pyrophylite
and about other duets of ingredients.
Whiting is Calcium Carbonate and shrinks a lot.
Wollastonite is calcium and silica and shrinks far less.
Dolomite is calcium and magnesium ans shrinks a lot.
Talc is magnesium and silica and shrinks far less.
Pyrophylite shrinks less than clay. =20
So. C'est tr=E8s possible that:
The original recipe with Wollastonite needed more flux- whiting added.
It is possible that the original recipe called for ALL whiting and
crazed and Wollastonite was used to replace whiting and cure crazing.
It is possible that YOUR recipe is the result of a straight line or
triaxial blend and the originator did not feel like recalculating.
And sometimes for reasons I do not know replacing an ingredient with the
"same" from another source gives a nicer effect. Or why molecular
formulae are not the perfect answer....
Lili Krakowski
Be of good courage
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