Does anyone know what
CoE means?
·
First the proper abbreviation is CoLE.
·
This means Coefficient of Linear Expansion.
·
A coefficient is an average. This number may be exact at a given temperature, or an average over a
range.
·
Linear is the length.
·
Expansion is measured in fractions of a metre e.g.,
0.0000096 metre.
·
The coefficient is given as the average amount
of expansion per each degree Celsius.
The temperature range used is 20C to 300C. Expansion characteristics vary greatly at higher temperatures.
The temperature range used is 20C to 300C. Expansion characteristics vary greatly at higher temperatures.
So CoE is the average amount (in metres) that glass expands for
each degree (Celsius) increase in temperature from 20C to 300C.
Whether you call it CoE or CoLE is immaterial, as it still does not equal compatibility.
It does not measure viscosity. Viscosity is a (possibly the major) element in making a range of compatible fusing glasses.
It does measure expansion rates, but up to 300C only. It does not tell you how glass expands above that temperature. Note: it does not behave in a linear pattern as crystalline materials do.
The CoE must be adjusted to match the viscosity to achieve
compatible glass. Spectrum has stated
that their glass has a range of CoE of at least ten points to make compatible
fusing glass. Bullseye have stated
their range to be 5 points. They also have indicated their base glass is nearer to 91 than 90.
The only constant required in fusing glass is compatibility.
CoE varies within each manufacturer’s range of fusing
compatible glass to match the viscosity. And remember the CoE of glass at the critical annealing point is higher than the low temperature expansion rate. See this post for details.
Viscosity varies according to the materials used in the
colouration of the glass and their proportions, requiring the glass manufacturer to make adjustments in CoE to get compatible fusing
glass. More information here.
CoE does not mean compatibility. It does not measure volume expansion at the glass transition point. It does not measure the most important element
– viscosity. It is not even the correct
term for the measure – CoLE is.
Since CoE does not mean a fusing compatible glass, its
continued use can lead people (especially novices) to believe the simple number
means any glass labelled with that number will be compatible with
others so labelled. This leads to
unexpected incompatibilities for newcomers to the field.
My plea is: STOP USING COE TO MEAN COMPATIBILITY.
What can you use instead? It is easy – use the manufacturer’s
name. Where the manufacturer is making
more than one range of fusing compatible glass use the manufacturer’s
nomenclature.
Please: STOP USING COE TO MEAN COMPATIBILITY.
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