Fay & Ralph Loewenthal on thu 16 aug 01
Dear Tom I posted this answer a short time ago.=20
The reply was for slumping glass, but is also true
for fusing. The additional information that you need
for fusing is that you have to be very sure that you
use glass that is of the same COE (coefficient of
expansion). This is usually from one manufacturer,
and one type of glass. You will have to check with
the manufacturer. I also thought I could fuse glass,
and not use the lead as in stained glass=20
applications. For the most part it did not work, You
have be extremely accurate with temperatures, and
by the time the glass has fused it could have=20
moved, and you do not have the result that you=20
would like.
Here is the reply I postedJuly 15th:
Dear Clayarters who are interested in glass, a lot of the
knowledge you need will be gained from experience, either
your own or somebody else's. I raided the city library and
read and photocopied whatever I could on glass. I have=20
about six lever arch files full of photocopies and they still
do not give the full picture.
First off keep in mind that you are working with glass or in
our terminology glaze. Every different type of glass has
different rates of expansion and contraction. If you mix two
incompatible glasses, they do not just craze, they crack into
many pieces. Always do tests first on small samples to=20
make sure of compatibility and the temperatures.=20
There are two options with slumping, you can slump over
stainless steel or into clay. Glass contracts more than clay,
and less than stainless steel. Whatever mould you are using=20
you need to coat it with kiln wash. I use a kiln wash that I
got from Don Jung, also a Clayarter. I just dip my clay=20
moulds into the kiln wash. The stainless steel moulds I heat
up in the kiln or oven to about 200 C, then dip it in a=20
diluted kiln wash. I picked up a lot of cheap stainless steel
moulds in second hand stores. I slab roll my grogged clay=20
and then cut out doughnut like rings of different diameters.
I just bisque fire them a lttle higher than the normal bisque
temperatures, so that I have reasonable strong mould. I=20
slump through these rings to make some rather attractive
vases.=20
Always make sure your edges are clean and smooth before
you do any kiln work. They will look worse after firing.
I fire according to the size of the pieces. The larger the
piece the slower the firing up. If you have a kiln that is not=20
electric or has elements in the lid or roof, then you can fire=20
faster. I fire any piece over 35 centimetres, 14 inches, in=20
diameter, at 50 C for half an hour and up it by 50 C every
half an hour till I reach the required slumping temperature.
I normally use window pane glass, slumping starts at about
750 C and it is usually finished at about 850 C. I flash the
kiln once I feel the piece is ready. I leave the door open till
the the tempeature had dropped to 500 C. I soak for two
hours at 500 C. I leave the kiln closed till the temperature
has dropped to just above room temperature. This is to=20
anneal the glass. If you do not anneal properly the glass
will eventually crack and break. This can happen even=20
months after the firing, so be warned. My temperatures are
all for our local window pane glass and in centigrade. You
have to check with your local glass manufacturer what=20
temperatures to use. Bottle glass uses higher temperatures,
and art glass usually uses lower temperatures.
Here is the kiln wash recipe:
Combo Kiln Wash:
Alumina hydrate 40
EPK 30
Kyanite (35 mesh) 8
Silica 22
Hope this helps if you need any more info just email me,
and I will help if I can.
Kind regards from Ralph Loewenthal in Cape Town
reiki54 on wed 19 jun 02
Hi, yes, i am have done glass fusing and slumping in a gas kiln, it was
many years ago and had some great results. I think it was done with
fairly low cones, can't remember exactly what the numbers were, but
with research you can find out how high to go.
Have fun with it, Tish Cook
Mercy Langford on wed 19 jun 02
Hi- i know nothing of glass-but I saw a craft show recently on tv and a
rather popular artist who did glass stated that she put the glass over the
mold and fired to 1400 degrees. Mercy
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