iandol on sun 24 aug 03
Dear Edouard,
Thank you for relaying this message from Smart C.
I have no quarrel with Smart's experience and accept what he says
about the behaviour of maturing glazes though I have always accepted
that once clay had De-hyroxylated during a bisque re -hydration did
not occur. Has Smart validated this with chemical analysis? It is like
saying that if I heat a crystal of clay to 900 deg C the powder which
forms will recrystallise as Kaolinite if I add water. Is this true?
Perhaps water which is issuing and causing porosity in low fired
glazes is moisture from drying after applying the glaze? There will be
far more of this when the application is by dipping than that applied
by spraying. (Just applying the "Kiss" principle here !!!)
His description of experiments which compare and contrast sprayed and
dipped specimens seems sound. A good way to find out the optimum rate
of firing in an industrial situation where efficiency and profit must
be achieved
I also understand why there is a need to take care when glaze firing
Earthenware because of the low Glass Transition Temperature of many
frits. I also accept that there is need for time at the best
temperature to allow the healing of bubble scars.
You will recall that my concerns were about the assumptions relating
to the application of glaze slop to bisque ware.
Smart claims that there are differences in surfaces which are Sprayed,
Dipped and I would imagine, Brushed.
He attributes these differences to the changes in surface tension as
the particle size is reduced.
I wish to know what data he used in his thermodynamic calculations and
how this was obtained.
He also claims that Surface Tension causes segregation, that Surface
Tension causes the fine particle to flow to the surface and allows the
coarse material to remain in the body of the slop. How was this
determined?
I would also like to know how he found out that as spray particles get
smaller the layer of fines at the surface reduces to zero, I quote
<impoverish more and more the mass of its finest minerals, since the
volume of the drops decrease more quickly than their surface.>> Where
does this material go to?
By the way, the relationship between area and volume remains constant
regardless of dimensions, be it a sphere, cube or prism or a blob of
glaze. But when a Specific Volume is repeatedly subdivided the
Absolute Surface Area increases. Eg...A cube of 1 cm edge has a volume
of one cubic centimetre. This cube has a surface area of 6 square
centimetres. Divide it into a cubes of half a centimetre along their
edges. Each smaller cube is one eighth of a cubic centimetre with a
surface area of one and a half square centimetres giving an absolute
area of 12 square centimetres for the whole cubic volume of one cubic
centimetre. By the time you reduce your one cubic cm. to micron sizes
the area is magnified a million fold or so.
I think Smart needs to return to his research and reconsider what
assumptions he has made as well as read literature relating to Surface
Tension and The Second Law of Thermodynamics and its application.
There is a philosophic admonition which is defined by the term
"Ockham's Razor" which we should all apply when doing out research.
But he has brought up an interesting phenomenon which deserves to be
investigated. I think It is worthy of more work.
Best regards,
Ivor Lewis. Redhill, South Australia
Edouard Bastarache on mon 25 aug 03
Hello Ivor,
I have just forwarded your message to Smart.
Later,
"Ils sont fous ces Quebecois"
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://sorel-tracy.qc.ca/~edouardb/
http://perso.wanadoo.fr/smart2000/index.htm
@pclink.com.
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