Gaffer® Glass Quality Control and Compatibilty Testing Glass starts with a careful selection of the purest raw materials, which are weighed into a mixer located on load/weighing cells to guard against weighing error. After thorough mixing, the batch is melted in the highest-grade refractories, according to carefully reproduced melt parameters.

Time/temperature and exactly measured redox conditions, ensures that each colour shade is very accurately replicated. All melts are fully homogenised. During working out, bubbles are blown regularly to inspect for cord, seed and stones. Further scrutiny of opaque and densely coloured rods follows, utilising ultrasound inclusion technology.

Concurrent tests are run for compatibility. Each coloured melt is evaluated using a polarimeter, referenced against a transparent Gaffer master glass (see Gaffer Batch). The measurement of mismatch is read as a measured polarmetric number, i.e. degrees of retardation in nanometers/centimeter. We aim to have a mismatch reading no more than 30 nm/cm, which for most glasses is roughly a linear expansion coefficient (LEC) difference of ± 0.5 x10-7 up to the strain, or set point, of our colored glass range. That is well inside a mismatch of ± 2.0 x 10-7, which is claimed to be the outer limit of acceptable thermal mismatch difference, (although we disagree; ±1.5 is safer) and clearly superior to the 7-8 point spread that we have measured taking random samples from our raw colour competitors.

Only after performing this daily test and seeing the result we require, does the melt get released onto the global market. The colour bars are for glass blowers and are clearly labelled "Tested: Compatible/Ultrasound", meaning they have passed both the trident seal test and have been checked by an ultrasound scanner for excessive seed.

Be assured: all frits of blowing glasses are also compatibility tested.

All casting glasses, both frit and billets, meet an even higher standard: that is less than a 10nm/cm mismatch, which is less than 100psi strain in a casting format, nearly ten times below what is considered to be safe and acceptable (1000psi).

The coloured flashing or blowing glasses we produce should preferably be used in conjunction with a generic soda/lime etc. base clear, showing a measured expansion of around 96 x 10-7 (0-300ºC) and an annealing point around 485-500ºC (905-932ºF).

Copyright: Gaffer Coloured Glass Ltd.