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First Photoconductive CopyThe first photoconductive copy was made October 22 1938 by Chester Carlson in the state of New York. The technique began with the preparation of a photoconductive, sulfur coated, zinc plate. The item to be copied was a glass microscope slide on which a notation was written in opaque ink. The zinc plate was given a surface charge of static electricity by rubbing with a cloth and was then coated with lycopodium (very fine fungal spores) powder attracted by the charge on the surface. The glass slide was then placed on the zinc plate, and was irradiated briefly by a bright electric light. The zinc plate became (photo) conductive in those areas illuminated by the light, and remained an insulator under the area obscured by the notation on the slide. The surface charge of static electricity was discharged on the area of the plate exposed to the light and the lycopodium powder there was blown away. The remaining lycopodium powder firmly attached to the unilluminated area was the desired copy of the notation on the plate. To make a permanent copy the residual lycopodium powder was transferred to a sheet of wax paper, which paper was then heated to fuse the wax and the powder. These events and the resulting small copy provided a proof of principle which led to the development of the modern dry photocopying industry.
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