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Casting on glass


#1

Hi

I have been given a broken glass ring - broken whilst clapping hands
which means the shank has almost gone. I’ve been toying with the idea
I might use the delft clay mould but leaving the ring in situ whilst
pouring the molten silver to attach to remainder thus forming a new
shank. Would that work? Any advise greatly received!

Gill Bridgestock
www.gillbridgestock.net


#2

I’m afraid it will invariably fail for several reasons. Firstly, the
liquidus point of the glass is well below the melting point of silver
so the glass will at best deform and at worst end up as a blob,
secondly, the difference in thermal expansion will cause it to break
on cooling and thirdly, the silver and glass will react leaving a
horrible brittle oxide layer. If you try pouring the metal on to
(relatively) cold glass the thermal shock will cause it to explode
and giving a very real possibility of serious injury.

Better give it back to the customer and point them in the direction
of a bead maker or glass artist. Even then, without knowing the
coefficient of expansion of the glass the repair may prove impossible
unless you have the broken pieces to do heat tests on. I would be
tempted to try making a bound shank out of wirework and cut a groove
in the remaining glass to anchor it to. Without seeing the ring
remains it is difficult to suggest anything else,

Nick Royall


#3
I have been given a broken glass ring - broken whilst clapping
hands which means the shank has almost gone. I've been toying with
the idea I might use the delft clay mould but leaving the ring in
situ whilst pouring the molten silver to attach to remainder thus
forming a new shank. Would that work? Any advise greatly received! 

That’s a very interesting experiment, let me know how you go.

Not sure how the mystery glass would hold up if molten silver (fine
or sterling) poured onto it.

I’m very interested in the results though. Good luck.

Regards Charles A.


#4

Consider Precious Metal Clay.

You can sinter PMC as low as 1,100deg F so shaping a shank around the
remaining piece of glass will not be a problem.

Debbie
http://www.pmcafrica.blogspot.com


#5

I have worked with both glass & metals for a long time. I know from
experience that the glass would most probably shatter from thermal
shock. It really can’t take the heat fluxuation that molten silver
would give it. If you considered “cast in place” in a mold I would
then be concerned the glass would have a problem with the investment
and perhaps need to be completely re-polished, if it survives the
burn out process at all.

I am thinking perhaps make a shank of silver with open cupped ends,
and use an archival adhesive, maybe hyxtal, or another long lasting
epoxy would do the trick. Fabricate the shank with fitted "cup-like"
ends to hold in the glass portion and you could even drill the glass
with a diamond tip burr (of course in a dish of water, so as not to
make it shatter from the heat of drilling) and then run a rivet
through it for a more permanent hold.

Just a few of ideas for you.
Teresa


#6

Thanks Teresa for your comprehensive advice, I was beginning to
wonder if that would be the case. Your suggestion to make a silver
shank and then rivet for a more permanent hold sounds good.

Best regards
Gill

Gill Bridgestock
www.gillbridgestock.net


#7

Give it up. It broke the first time, didin’t it? The need and time it
takes to be annealed for the glass would probably firescale the heck
out of the silver even if the glass survived… sheesh. Would you
want to be liable if it broke the second time and took some finger
with it? Some things just aren’t meant to be. And no, i’m not a
negative person. I just worked in a glass factory for 35 years and
have seen all sorts of things…


#8

Hi Debbie, you must’ve been reading my mind as I have been wondering
about using PMC, I have a micro-kiln could I use that for the whole
ring or should I fire with a torch thus aiming the heat directly
onto the PMC shank?

Many thanks
Gill

Gill Bridgestock
www.gillbridgestock.net


#9

If you really want to persevere with this project, do run trials
first with glass and pmc.

Go to a mall and buy some similar rings, there only a dollar or 2,
experiment with them FIRST before you waste too much time on what to
many of us professionals here consider to be a waste of time. As a
professional you must make it clear to the customer you either do the
job on a fixed price basis, and your sure you have done your sums
correctly, or you charge by so much per hour like a profesional
person ie, lawyer accountant, doctor etc and the Professional crafts
person, ie carpenter, plumber etc.

Otherwise your really running a charity with no income. Have fun.

Apologies for the double post, computer glitch, and a bit of anno
domini.

Ted


#10

Gill,

It wont work, the PMC sintering temp is too high for the glass to
withstand and the metal will react. You cannot make a shank form
metal using heat with this glass. Cold forming your metal shank is
the only way and that will not be worth the effort. Get a
glassworker to look at it or keep the head of the ring and glue it on
to a shank.

Nick Royall


#11

It will be a big problem as the difference in thermal expansion will
mean that it will not stick. Also, silica goes through a phase
change at 500 deg c and this again causes problems with
expansion/contraction. The glass will start to flow at just under
1100 deg f so any prolonged heating even to this temp will cause the
glass to deform significantly.

Dont do it, it will end in failure.


#12

Thanks guys, I am sufficiently convinced to “walk away from the
glass ring”. However it has certainly brought up some very
interesting facts and figures…you learn something every day! Gill

Gill Bridgestock