Gaffer® Glass Quality Control and Compatibility 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 color shade is very accurately replicated. All melts are fully homogenized. During working out, bubbles are blown regularly to inspect for cord, seed and stones. Further scrutiny of opaque and densely colored rods follows, utilizing ultrasound inclusion technology.

Gaffer Glass carries out the same thermal mismatch test as Corning Inc, employing a polarimeter and a trident seal. This test bypasses dilatometersand viscosity meters, which are notoriously inaccurate. By contrast, the trident seal produces an easily read and very accurate control. Any studio can fashion it cheaply and accurately. The seal can be passed on to a third party, where the results can be compared under the same conditions. It takes care of different viscosities and variable properties such as Young’s modulus and surface tensions.

Each colored 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 color competitors.

Only after performing this daily test and seeing the result we require, does the melt get released onto the global market. The color bars are for glass blowers and are clearly labeled "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 colored 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).

* The Trident Seal Test performed by Gaffer® Glass

Copyright: Gaffer Coloured Glass Ltd.