Gas lamp glass

I have been asked if I can make some replacement glass for an old gas
lamp. The lamp forms a truncated cone about 380mm (15") high, 230 mm
(9") at the base and 430mm (17") at the top. 3 pieces of glass form the
cone and are fixed to 3 vertical ribs joining the top and bottom of the
lamp. I have done some straight 'U' shaped glass before but that was to
be sand blasted and so the internal surface finish was not an issue, I
just slumped it over a sheet steel former coated in kiln shelf wash and
it worked perfectly. These items want to be quite smooth and I am not
sure how the original would have been done. The only remaining damaged
one shows the side of the cone to be quite straight. I wonder about
making a form to represent the edges and slumping over this but fear the
glass will sag in the centre and so the side of the cone would not be
straight. Any ideas how these would have been produced, maybe over a
form with a very fine surface so as not to impart any texture on the
glass.

When originally made, they were probably slumped into an iron mold coated
with release. They may have been heated to nearly soft and moved like a
pizza onto the mold. In modern terms the release has to be coated several
times and brushed smooth and slightly dusty. A curved piece of stainless
steel is probably your best mold for a smooth curve. You may want to
partly slump the piece over rods to pre shape it although a 1/3 mold should
not be bad.

--
Mike Firth
Hot Glass Bits Furnace Working Website
http://users.ticnet.com/mikefirth/hotbit46.htm Latest notes

"David Billington" wrote in message
...
I have been asked if I can make some replacement glass for an old gas lamp.
The lamp forms a truncated cone about 380mm (15") high, 230 mm (9") at the
base and 430mm (17") at the top. 3 pieces of glass form the cone and are
fixed to 3 vertical ribs joining the top and bottom of the lamp. I have
done some straight 'U' shaped glass before but that was to be sand blasted
and so the internal surface finish was not an issue, I just slumped it over
a sheet steel former coated in kiln shelf wash and it worked perfectly.
These items want to be quite smooth and I am not sure how the original
would have been done. The only remaining damaged one shows the side of the
cone to be quite straight. I wonder about making a form to represent the
edges and slumping over this but fear the glass will sag in the centre and
so the side of the cone would not be straight. Any ideas how these would
have been produced, maybe over a form with a very fine surface so as not to
impart any texture on the glass.

David,
I have made these from time to time over the years, and they are pain to get
just right.
So don't try to get perfect in the bending process, make them oversize and
trim later.
As for the moulds, well, the sheet metal guys have fun making these for me !
: )
BTW, for bending temps, you shouldn't need to kiln wash at all.
There are little things to stop pitting etc on the glass too, though
sandblasting after is a great effect anyway.
Moulds can be s/s (best but pricey) or z/a, even mild steel can be used, if
z/a (burn z/a off first) or mild steel, give then a rub before slumping.
Regards,
Les

"David Billington" wrote in message
...
I have been asked if I can make some replacement glass for an old gas
lamp. The lamp forms a truncated cone about 380mm (15") high, 230 mm
(9") at the base and 430mm (17") at the top. 3 pieces of glass form the
cone and are fixed to 3 vertical ribs joining the top and bottom of the
lamp. I have done some straight 'U' shaped glass before but that was to
be sand blasted and so the internal surface finish was not an issue, I
just slumped it over a sheet steel former coated in kiln shelf wash and
it worked perfectly. These items want to be quite smooth and I am not
sure how the original would have been done. The only remaining damaged
one shows the side of the cone to be quite straight. I wonder about
making a form to represent the edges and slumping over this but fear the
glass will sag in the centre and so the side of the cone would not be
straight. Any ideas how these would have been produced, maybe over a
form with a very fine surface so as not to impart any texture on the
glass.