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Recycling broken glass to make beads


I have a safety question. I’ve found all manner of glass that is
thrown out on a daily basis: coke bottles, depression glass, vases,

I realize that NONE of it is COE-90, and so I cannot count on any
reliable measure for time, temperature, etc.

But just how unsafe is it really to use anything other than
calibrated glass stock for melting in a kiln to make beads and such?

If not unsafe but just different, can anyone provide me guildelines
on how best to melt and fuse together bits of random recycled glass?

Thanks in advance,
Andrew Jonathan Fine

There are thousand of different types of glass, many made for
specific purposes and not very good for anything else. Bottle glass
is an example of this, it has a relatively high liquidus point but
then flows readily and need little or no anealing. When you remelt it
you tend to get a little devitrification on the surface which leaves
an oxide layer making it difficult to rework in small amounts. If you
try mixing it with other glasses for beadmaking or slump casting or
the like the glass will often violently shatter as the internal
straining becomes too much, just like toughened glass or Prince
Ruperts Teardrops. This is why mixing glasses with different COE’s is
unwise. Now, there are lots of waste glass you can use with effort-
borosilicate glass does make good beads but you need to use an
oxypropane torch of reasonable size to get the glass melted. The
higher RI of the glass makes for bright beads and annealing is not
that important on small pieces. Decorative cast glass can be
reworked and older pieces tend to be made of the same types of glass
so are miscible with each other. Occasionally you will come across
some oddball pieces- I made some lovely items from Venetian glass
cullet that was left over from a scientific appraisal of an
archaeological site. A glassblower whom I know well made some
replicas of Venetian goblets and reckoned it was the best glass he
had ever worked with once he got used to it. I made some beads and a
couple of cast ornaments. High melting point compared to art glass
but no problems like you get with bottle glass.

Nick Royall

Andrew, if you use glass by manufacturer - i.e. only coke bottles
with other coke bottles - you may be ok. melting isn’t the biggest
issue, annealing it is. you should do test pieces and then check for
stress with a polarizer after different time periods. as for vases,
depression glass, etc, using it with only itself should work, trying
to put glass from different pieces together is going to be riskier.
if you are working with 90 coe already, test using your current
firing schedules and record the results and adjust as necessarily.
you may be able to find out more info here from others who are/have
working/worked with recycled glass:

Dee Janssen
Dee Janssen GlassWorks

Hi there: I don’t make beads, but I do make cabochons out of glass
from wine bottles. I only use glass from the same bottle, as you
already know that it’s the same coe. If you start mixing & matching
different glasses from different bottles you may have issues
immediately, in a month, 6 mos. etc. w/ devitrification and/or
breakage. Enjoy!