Lyn Packer on mon 4 oct 99
Hi, Would anyone be able to give me advice on slumping small whole glasses
on to glazed, fired dishes/plates? The glasses I have tried using {glass and
crystal}, slumped quite nicely, but crazed badly {too thick I suppose}. Also
they become after a while, opaque or milkiesh. I can't remember the temp I
used, but think I have tried between 800oC and 1000oC. I know that I should
write all experiments down. I make sure that I cool very slowly. I have seen
a photo of some done in a book, and they don't appear to be crazed, but
probably are a little. Also they seem to be clear, glass looking. I realise
that they would not be functional, but well, it's good to do some fun pots
too. TIA
Lyn
lyn.packer@clear.net.nz
Khaimraj Seepersad on tue 5 oct 99
Hello Lyn ,
to stop the crazing you would have to use a clay body that is higher or
equal
to the expansion of your glass .
As to the whitening , I am sure the others know the term , but simply , you
have to remelt the glass to get it back to clear .
For my Coca Cola bottles that is usually after 1100 deg.c or after cone 04 .
Your response , noted at 800 to 1000 deg.c , is dead on to what I have
observed . You should however get a better response with true Lead
Crystal m.p is supposed to be around 950 deg.c .[ will still release Pbo
like a glaze , I read this , I don't work with lead ] .
You would see this as normal glass cullet , applied as glaze -
100 % [ -200 mesh ] cullet + 5 % white bentonite [ not white firing ]
700 to 750deg.c - gloss . - easily scratched by a sharp knife .
800 to 850 deg.c - losing gloss , going white - knife effect same .
850 to 900 deg,c - opaque to translucent white - knife same .
900 to 950 deg.c - more translucent - knife some resistance .
950 to 1000 deg,c - more translucent , gloss returning - knife resistance.
1000 to 1050 deg .c - almost clear - gloss - knife skidding off .
1050 to 1100 or so - clear - gloss - knife skidding .
Will run after 1150 to 1200 deg .c .
Please note there maybe a 30 to 50 deg.c + or - , at all end temperatures
for extra radiant heat . eg . 700 deg.c maybe = to 730 to 750 deg,c .
My test kiln is very small and the pyrometer is old .
Tests done on a Red High Fire earthenware [ to 1150 deg.c ] by cone
in a normal electric kiln.
All glazes cracked . Clay was vitreous .
Addition of 10 % kaolin , allowed the glaze to go past 1150 deg.c .
* all Coca Cola bottles will scratch with a knife , if worked on the same
spot .
Probably not quite what you expected , but hopefully , this will help you
to understand glass a bit more .
Khaimraj Seepersad
-----Original Message-----
From: Lyn Packer
To: CLAYART@LSV.UKY.EDU
Date: 04 October 1999 15:43
Subject: slumping glasses
>----------------------------Original message----------------------------
>Hi, Would anyone be able to give me advice on slumping small whole glasses
>on to glazed, fired dishes/plates? The glasses I have tried using {glass
and
>crystal}, slumped quite nicely, but crazed badly {too thick I suppose}.
Also
>they become after a while, opaque or milkiesh. I can't remember the temp I
>used, but think I have tried between 800oC and 1000oC. I know that I
should
>write all experiments down. I make sure that I cool very slowly. I have
seen
>a photo of some done in a book, and they don't appear to be crazed, but
>probably are a little. Also they seem to be clear, glass looking. I realise
>that they would not be functional, but well, it's good to do some fun pots
>too. TIA
>
>Lyn
>lyn.packer@clear.net.nz
>
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