Patent GB-654740-A (GB)
Title: Improved manufacture of photosensitive glasses and articles made thereof
IPC: C03C4/02
Filed: 1948-10-01
Abstract: 654,740. Photosensitive glasses. CORNING GLASS WORKS. Oct. 1, 1948, No. 25636. Convention date, Jan. 9. [Class 56] [Also in Group XX] A photosensitive silicate glass containing Au, Ag, or Cu, as a primary sensitizing constituent and CeO 2  contains also up to 0.1 per cent. by weight of Sb 2 O 3 . The glasses when exposed to short wave radiations and then heated become coloured in the irradiated areas while the non-radiated areas are unchanged. The Sb 2 O 3  improves the photosensitivity and eliminates bubbles, but more than 0.1 per cent. Sb 2 O 3  decreases the photosensitivity and 1 per cent. of more destroys it. The invention is effective in silicate glasses and particularly in those containing one or more of the oxides of Be, Mg, Ca, Zn, Sr, Cd, and Ba. When gold is used the Au content is 0.01- 0.1 per cent., preferably 0.02-0.03 per cent or more destroys it. The invention is sensitivity. The Ag content is about 0.05- 0.3 per cent. calculated as Ag Cl, and is preferably introduced as the chloride. When Au or Ag are used the batch preferably contains an oxidizing agent, e.g., alkali metal nitrate. The Cu content is about 0.05-1.0 per cent. calculated as Cu 2 O, generally about 0.5 per cent. Cu 2 O is used, but up to 1 per cent. or more may be used to make photosensitive glass fabrics, and with Cu a reducing agent, e.g., NH 4 Cl or sugar is included in the batch. Up to 0.05 per cent. CeO 2  increases the exposure speed ten fold, but more than 0.05 per cent. inhibits photosensitivity. SnO 2  may be used but is about half as effective as CeO 2 , more than about 0.02 per cent. SnO 2  in Au and Ag glasses destroys photosensitivity by causing coloration, but the Cu glasses may contain 0.5 per cent. or more SnO 2 . The oxides of As, Fe, Mn, V, Se, Tl, and U should not be included, and PbO in amounts greater than 1-2 per cent. is prohibitive. Au and Ag may be included together but neither should be used with Cu. Up to about 1 per cent. of sulphate, e.g., CaSO 4  or salt cake, improves the firing rate. The glass may be thermally and controllably opacified to produce a white background by including Fluorine in the composition, these batches are melted for about 4 hours at 1350 C. to produce colourless and transparent glass which when reheated at 500-600C becomes opaque or light diffusing. Chloride assists the opacification and NaCl is added if the batch does not contain NH 4 C1. The glasses are exposed to short wave radiations, e.g., carbon ore, quartz mercury ore, X rays, or radioactive radiations, the exposure varying according to the intensity of the radiations. The subsequent heat also varies, 500-600C being the most suitable temperature range, and 30 mins. at 550C an average treatment. Cu glasses develop red shades, Au varies from blue-lavender-purple-maroonred, and Ag bright yellow or amber. Photographic negatives can be used in the normal manner using on UV light source or direct sunlight to produce heat developed images on the glass. The compositions of several batches are given. Specification 636,152, is referred to.