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[How2?] Polish a Glass Cab


#1

Hi Rene: Can you tell me how to polish a glass cab, is is
possible with a buffing machine and what special wheels etc. are
needed. I collect one of the first synthetic opal jewelry, I call
it butterfly glass and was mainly set in sterling, A very pretty
glass.

Thanks
Chris
http://www.tace.com/glitters


#2

Chris (and others who are interested in lapidary work with
glass): You can cut, facet, grind, polish, etc. glass just as if
it were stone. (Depending on the kind of glass, it is usually
somewhere between 5.5 and 7.0 on the Mohs scale.) The technical
glassworking term for this is “coldworking”. However, you must
use diamond equipment for sawing or grinding, and/or silicon
carbide as a grit on lap wheels for polishing. And you absolutely
must work with water as a lubricant. Unlike stone, glass will
fracture from the heat buildup of cutting, polishing, etc., so
the water is not just a lubricant, but a coolant. Oil will hold
the heat too much. Usually people who do this kind of work use
special equipment designed for working with glass. You can’t do
it on a regular buffing wheel, and compounds which will polish
metal or some stones generally won’t work on glass.

If you just want to work at the scale of glass cabachons, then
your easiest, cheapest option would be to invest in a set of hand
held diamond sponge pads available from Wale Apparatus (Phone #
is 1-800-334-WALE). These are called “diamond handpads”) and come
in grits from 60 to 1000. These pads are made in finer grits than
1000, and Wale may now carry finer ones; but if not, try some of
the lapidary companies which advertise through Lapidary Journal.
(In one of the issues this past summer, some of these handpads
were shown on the back cover in an ad for a company which carries
this kind of stuff.) Companies which carry stoneworking equipment
for headstones and stone sculpture also carry these pads. Expect
to pay $15 - $20 per pad, depending on the grit size. You can
also buy diamond “files”, which are little miniature pads on
plastic sticks, and these offer you a lot more hand control, but
for the money, your sponge handpad will last a lot longer. The
diamond wears out pretty quickly. (The files also don’t come in a
lot of grit sizes.) Don’t forget to work completely under water.
It isn’t enough to just have the piece a little moist. You won’t
break the glass if you’re grinding dry by hand, but you will
trash the diamond pad. As far as attaching your cab to something
so you can handle it, you can try dopping wax, but I don’t know
the temperature this needs to melt, and any abrupt temperature
change could thermal shock the glass. I think there are things
like chunks of shellac which can be stuck on and then dissolved
later in denatured alcohol. This would be your safest bet. I have
simply hand-held the things I’ve ground with pads.

If you’d like to try a mechanical method of grinding and
polishing and don’t want to spend a lot of money, Arrow Springs
(Phone # 530-677-9482) carries an inexpensive beveling machine
which comes with several wheels. I think it sells for between
$150 and $200. However, it may be difficult to get a cab with an
evenly domed surface by machine; the machine would be much more
suitable for faceting.

If you have a kiln and can get your cab to a decent surface
without scratches (e.g. 600 grit) by mechanical means, then you
can also bring it up to a high shine by fire polishing (don’t try
this with a torch; you’ll break the glass). If you’d like more
info about this, email me and I’ll go into more detail.

I think I saw Bob Aurelius’ name floating around Orchid - he
does a lot of glass faceting and working with large glass beads
like Maybe we can coax him out of hiding to tell us
more. I do a limited amount of coldworking, so am not completely
familiar with all the equipment options on the market.

Hope this helps (and isn’t gobs more than you really wanted to
know . . .)

Rene


#3

You can fire polish a glass cab with a torch without breaking
the cab. The trick is to bring the cab up to temperature very
slowly. Really, v e r y s l o w l y! Glass, even the small
amount in the cab will thermal shock very easily. Wear eye
protection. Start out by setting the cab on a warm hot plate.
Let it warm for a short time, then turn the hot plate up to
medium heat, and bring it up to high heat within a few minutes.
Then, brush your flame over the cab until it warms further. You
will need to be very patient. Once hot you can circle the flame
over the cab to heat it evenly and obtain your fire polish. No
need to overheat or you will end up with a misshapen cab. (If
you are going to try this, e-mail me off list and I will attempt
to describe how the glass looks when you reach a polish.) Also,
when you are finished with the fire polishing, you must anneal
the cab, or it will crack or break. It may not do it right
away, but the internal stress will remain in the glass and it
will find its own opportunity to break. This is easier than it
sounds. As soon as you remove the flame from the cab, bury the
hot cab in a bed of vermiculite and let it cool slowly. (Make
sure the cab is not too hot when you pick it up or your tweezers
will distort it.) This should be sufficient to anneal such a
small amount of glass. Warning: one would usually use a
surface mix torch for glass and some colors of glass may discolor
due to the type of flame you use. Stay away from a real reducing
flame, but do not use a real hot, hissing flame either. Good
luck!

Also, I use cerium oxide on a chamois covered wheel (lapidary
set-up) to polish glass. You must have a “sprinkler” on it to
keep it wet so that it doesn’t overheat and fracture.

Laura Hiserote
http://www.micromosaics.com


#4

Chris (and others who are interested in lapidary work with
glass): You can cut, facet, grind, polish, etc. glass just as
if it were stone. (Depending on the kind of glass, it is usually
somewhere between 5.5 and 7.0 on the Mohs scale.) The technical
glassworking term for this is “coldworking”. However, you must
use diamond equipment for sawing or grinding, and/or silicon
carbide as a grit on lap wheels for polishing. And you
absolutely must work with water as a lubricant. Unlike stone,
glass will fracture from the heat buildup of cutting, polishing,
etc., so the water is not just a lubricant, but a coolant. Oil
will hold the heat too much. Usually people who do this kind of
work use special equipment designed for working with glass. You
can’t do it on a regular buffing wheel, and compounds which will
polish metal or some stones generally won’t work on glass.

If you just want to work at the scale of glass cabachons, then
your easiest, cheapest option would be to invest in a set of
hand held diamond sponge pads available from Wale Apparatus
(Phone # is 1-800-334-WALE). These are called “diamond handpads”)
and come in grits from 60 to 1000. These pads are made in finer
grits than 1000, and Wale may now carry finer ones; but if not,
try some of the lapidary companies which advertise through
Lapidary Journal. (In one of the issues this past summer, some of
these handpads were shown on the back cover in an ad for a
company which carries this kind of stuff.) Companies which carry
stoneworking equipment for headstones and stone sculpture also
carry these pads. Expect to pay $15 - $20 per pad, depending on
the grit size. You can also buy diamond “files”, which are little
miniature pads on plastic sticks, and these offer you a lot more
hand control, but for the money, your sponge handpad will last a
lot longer. The diamond wears out pretty quickly. (The files also
don’t come in a lot of grit sizes.) Don’t forget to work
completely under water. It isn’t enough to just have the piece a
little moist. You won’t break the glass if you’re grinding dry by
hand, but you will trash the diamond pad. As far as attaching
your cab to something so you can handle it, you can try dopping
wax, but I don’t know the temperature this needs to melt, and any
abrupt temperature change could thermal shock the glass. I think
there are things like chunks of shellac which can be stuck on and
then dissolved later in denatured alcohol. This would be your
safest bet. I have simply hand-held the things I’ve ground with
pads.

If you’d like to try a mechanical method of grinding and
polishing and don’t want to spend a lot of money, Arrow Springs
(Phone # 530-677-9482) carries an inexpensive beveling machine
which comes with several wheels. I think it sells for between
$150 and $200. However, it may be difficult to get a cab with an
evenly domed surface by machine; the machine would be much more
suitable for faceting.

If you have a kiln and can get your cab to a decent surface
without scratches (e.g. 600 grit) by mechanical means, then you
can also bring it up to a high shine by fire polishing (don’t
try this with a torch; you’ll break the glass). If you’d like
more info about this, email me and I’ll go into more detail.

I think I saw Bob Aurelius’ name floating around Orchid - he does
a lot of glass faceting and working with large glass beads like
Maybe we can coax him out of hiding to tell us more. I
do a limited amount of coldworking, so am not completely familiar
with all the equipment options on the market.

Hope this helps (and isn’t gobs more than you really wanted to
know . . .)

Rene


#5

Chris - I’ve just read Laura’s message about fire-polishing
glass with a torch. While she’s right about being able to do all
this with a torch, I’d just like to second a few things she said.
The success of this method depends on a lot of different
variables: thickness of the glass, annealing method (annealing
glass is not the same as annealing metal - the same word has two
completely different meanings), type of glass, color of glass,
type of flame. If your cabs are old (you said you “collect”, as I
recall), the glass may contain lead, which will likely turn to
grungy gray in a torchfire. I suggest you do a lot of practicing
with the torch before attempting to torch-polish a piece of
glass you care about.

If you have access to a small kiln, none of these variables are an
issue.

Rene