Edouard Bastarache on tue 26 sep 00
To Vivek
from sci.materials.ceramics,
Later,
Edouard Bastarache
Dans / In "La Belle Province"
edouardb@sorel-tracy.qc.ca
http://www.sorel-tracy.qc.ca/~edouardb/
-----Message d'origine-----
De : HRP >
Groupes de discussion : sci.materials.ceramics
Date : 25 septembre, 2000 19:50
Objet : Re: Scumming?
>Hamer (The Potters Dictionary of Materials and Techniques) suggests adding
>1-2% barium carbonate to the clay mix at the slurry stage and then blunging
>it. Mixing with the finished clay is not sufficient. The salts causing the
>problem are of sodium, potassium, calcium, magnesium and iron. The addition
>of barium carbonate renders them insoluble.
>Edouard Bastarache wrote in message
>news:7Snz5.683$m03.6252@wagner.videotron.net...
>> hi,
>> recently i had a problem with the saltglazed stoneware
>> sewage pipes that i manufacture. i think there is
>> something wrong with the fireclay that i used . this
>> is the problem.
>> when the pipes were extruded and dried in the sun
>> scores of handling marks were visible after drying and
>> when i looked at the surface with the magnifying glass
>> i could see small white specks very very tiny about
>> the size of pin holes on large parts of the surface.
>> Now when the kiln was fired and the sample was ripe
>> for salt to be added into the kiln, salt was added but
>> even after repeated salting attempts the sample could
>> not catch salt and ultimately we had to leave the
>> firing after wasting so much of coal.
>> the fired result was also horrifying. the pipes
>> instead of being a bright brown shiny colour were
>> white and at the most a light creamy or fawn colour
>> and all the handling marks and all sorts of marks were
>> visible.
>>
>> could anyone please advise me as to what may have gone
>> wrong. the temperature for salting also had been
>> reached and the kiln was fired exactly according to
>> our previous experience of about 20 years.
>> recently i read in a book by singer and singer that if
>> the clay contains more calcium and manganese salts a
>> sort of white scum of salt develops or comes to the
>> surface of the body thereby reducing the ability or
>> receptiveness of the body to salt. Must that be the
>> problem? i dont know i am confused.
>> the book also recommended quick drying of the ware so
>> that these salts do not have enough time to come to
>> the surface.
>> please help
>> any help will be appreciated
>> thanks
>> vivek patel
>>
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