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Blowing - Instructions for using Gaffer® Copper Ruby #075

Gaffer Glass has formulated a new copper ruby especially suited to the typical soda lime batches used in the studio. Because it has similar viscosity characteristics to a normal soda lime, there is less likelihood of the color overstriking during annealing heat treatment, and the red becoming too dark, dull, and possibly livery or ‘hæmatinone’. These faults are often due to the typical lead based copper ruby recipes having a much lower annealing temperature than the soda lime bases.

While Gaffer has made every endeavour to achieve the correct conditions when the glass was melted and worked out, we still depend on your efforts to achieve the best color. Unlike other striking colors based on gold, silver, or for that matter cadmium selenium glasses, which do not substantially change after they are struck under controlled conditions at our plant, copper ruby requires your input as well for the optimum results.

Copper ruby is naturally a strong color, and looks at its best when the flashing is blown evenly and thin (ideally no more than 0.5 mm for a closed form, and perhaps 1 mm for an open plate). Shorter working times tend to be favourable. The color will disappear on heating strongly, returning when allowed to cool and strike slowly. This is normal.

After the piece is blown, it is very important to experiment with the temperature and time in the annealer to achieve the right color hue and density. Too short a time at a low temperature i.e. below 480°C (896°F) and the color may not strike, or only with difficulty. Held for too long at 520°C+ (970°F+), and the color will possibly become too dark and dull, with a risk of slight opacity, particularly if the flashing is too thick. Be aware that too high a temperature in heat treatment, i.e.>600°C (1110°F) may prevent the color striking.

Most annealing ovens tend to be rather uneven in temperature, and several copper ruby pieces, put in different parts of the oven, will strike at different speeds and varying degrees of color intensity. Copper ruby is a very sensitive indicator of temperature gradations in annealing ovens. Experiment at first with a few test pieces. A ‘garage’ or ‘toaster’ can be a convenient tool for quickly observing the color dynamics. Usually, the color will go straight from clear to a growing intensity of blood red, with increasing time and temperature. Overstriking leads to opacity.

In our experience, under our conditions, the color will develop to a pleasing hue at approximately 500oC (932oF) over about 20-30 minutes, depending on the flashing thickness. If pieces are made towards the end of the day and annealing needs to get under way, then a short burst of heat up to 520°-550°C (970°-1020°F) will develop the color rapidly, after which the soak temperature can be rapidly lowered to the bottom end of the annealing range to arrest the color development and prevent overstriking (ie. 460°C).

Copyright Gaffer® Coloured Glass Ltd. 1998.

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