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Over
the last few years Gaffer® Glass has evaluated dozens of different
soda lime and lead based studio furnace glasses from the viewpoint of
expansion and viscosity characteristics. Our job as color bar manufacturers
is to somehow fit with quite a large bandwidth of expansion coefficients
out there. Unlike people who work with Pyrex, Bullseye, Spectrum 96,
or Moretti for example, there is no acknowledged “master glass” that
color bar makers can tune their glasses to. We therefore decided to formulate
our own “master glass”. Our research, both theoretical and physical, showed that the bell curve of linear expansion coefficients, melted in studios in the USA, Australia, New Zealand, Japan and England, peaked at around 96x10-7 (0-300oC) with the outer limits ranging from 94-99.5. Viscosity data, based on Lakatos’et. al factors,¹ also showed very wide variations at melt and working temperatures, ranging from 1290oC (2354oF) at log 2 (a measurement of viscosity in poises at upper fining temperatures), up to as high as 1430oC (2606oF). Not that we are suggesting that people are necessarily melting at those temperatures, but for the purposes of comparing apples with apples, the Lakatos calculations are instructive. The bell curve for the temperature at log 2 viscosity peaked at 1370oC (2498oF), with some commercially available batches in excess of that. Gaffer decided to set out designing a clear batch from scratch that would meet certain guidelines we felt were important and have the batch made available commercially by being manufactured by Philips (Code #3300) and Spruce Pine Batch in pelletized form. The criteria we considered important for a studio glass (not necessarily in order of priority) were the following: • Energy Costs |