coe and sag point and annealing point

Hi,

Could someone please provide some good sources to learn more about the
relationship(s) between the coe of various glasses and their sagging and
annealing temperatures...especially concerning practical means to determine the
coe of unknown glass...a particular book, maybe.

Thanks
Burl

There is no direct relationship between COE and sagging and annealing
temps, although roughly, the higher the COE, the lower the temps, as shown
most clearly with Pyrex with a low COE and higher temps.
Absolute COE is a laboratory process involving precise temperature control
and measurement and a certain amount of fudging in the case of fusing
because the measurement is done well below fusing temps (max 300C). COE can
also be calculated from the chemical formula, giving a different, but
predictably different, answer.
Relative COE is much easier and is the common test described in books -
fuse or melt together two pieces of glass and look at the result through a
polarizer and if there are no strain lines they have the same COE.

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

"Hankinson" wrote in message
...
Hi,

Could someone please provide some good sources to learn more about the
relationship(s) between the coe of various glasses and their sagging and
annealing temperatures...especially concerning practical means to
determine the
coe of unknown glass...a particular book, maybe.

Thanks
Burl