| Our Gold Ruby #221 and Gold Amethyst #276 casting crystal is specially designed to be "struck" under casting conditions. Gold ruby #221 comes in a very pale pink state. (It is doped with a small amount of Erbium to distinguish the glass from Clear #210). The Gold amethyst #276 shows the amount of cobalt blue in the glass that will turn the ruby into an amethyst. If we struck the glass before on selling it, then it would become "overstruck" under the extra heating regime of casting. Gaffer™ Glass Co. offers photosensitive glasses suitable for use as a casing glass for the studio glass blower. These are reworked formulas from the original recipes developed by Stookey at Corning during the Second World War, designed to be compatible with typical soda lime glasses. Particular attention has been paid to aligning the properties of expansion, viscosity and durability. As with any new technology it is important to follow the instructions explicitly. Please note that some base glasses (batch, cullet) contain chemicals that impede UV light transference. This will cause inferior results in the development process. Properties and Application Gaffer™ photosensitive glasses can be used in the same way as any other casing glass, either as an inner casing, outer casing, or interlayer casing. The glass is soft and easy to work. In order to exploit its properties, however, photosensitive glass must be exposed to an ultraviolet light in the finished piece and then exposed to heat for 3-4 hours at top annealing temperatures. Before the artist is ready to mask and expose a piece, it should be kept in the dark. It must also be kept in the dark until it is ready for blowing. After the piece has been blown, it must also be kept in the dark until it is ready to be exposed and developed. Although the glass is not nearly as sensitive to light as film, the ambient levels of UV light in a room will be sufficient to "spoil" the glass after a day or two. A "spoiled" glass simply becomes ordinary gold ruby, on being reheated, so it is not completely wasted. Exposure The exposure of photosensitive glass is in many respects similar to that of ordinary photographic material. It differs mainly in the fact that the exposure requires UV peak radiation, and usually requires considerably more exposure time. The wavelength of light required ( 300-350nm) can be supplied by sunlight (although sunlight may be too variable to be relied on). More consistent results are obtained by the use of commonly available florescent suntan tubes. Phillips TL40W/09 N low pressure mercury vapor florescent tubes are ideal. They are available in 600 mm lengths or longer. Other brands offer comparable specifications. Exposure distance of 100-150 mm (4-6 in) in about 20-40 minutes is sufficient for most effects. An even exposure of a vessel can be achieved with an old record turntable. The colors produced, the density of the hue, depend on exposure time and intensity, but also on development temperature and time. With gold ruby glasses, short exposures will give blue through purples; longer exposure will give true ruby coloration's. After UV exposure only a "latent image" results which is not visible. Development by heat is required. UV Resists Anything which resists UV light can act as a resist or negative. For photographic resolution the most efficient material is adhesive polyester as a reverse negative, available from office products & print suppliers. However anything which can stop UV is suitable. Felt tip pens, Letratone, bromides, masking tape, etc.are all effective to varying degrees. Development Unlike ordinary film, which requires chemicals to develop the image, photosensitive glasses simply require heat. The term "latent image," refers to the fact that simply exposing the glass to UV will make visible the color.. For the ruby glasses a temperature of 520 - 575 C / 975 - 1070F is required, over 3-4 hours. The higher the temperature, the quicker the development. (Areas that are closer to the heat source may develop faster than those at a distance .) The color centers are latent until developed by heat. If the glass slumps, simply lower the temperature and increase the developing time. Only by heating to the correct temperature for a long enough period of time will the latent image reveal itself. As with exposure, short heating times and exposure periods will produce blues to purples, with the gold ruby. Higher temperatures for longer periods will produce ruby colors. As with any new technology, it is important to experiment to develop the proper exposure and development cycles for the result that you want to achieve. Tip: To document the length of time needed for exposure, the use of stickers removed at different times will help you discover exposure time needed to produce desired hues and densities. As with any new technology, it is important to experiment to develop the proper exposure and development cycles for the result that you want to achieve. Tip: To document the length of time needed for exposure, the use of stickers removed at different times will help you discover exposure time needed to produce desired hues and densities. Copyright Gaffer™ Coloured Glass Ltd. 1998 | 
