We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
PHOTOGRAPHIC IMPORTANCE OF CHROMIUM COMPOUNDS 93
finding the right time for exposure, the proper consistency of the printer's ink, and other obstacles. After a hundred impressions, the film of gelatine was generally so injured that it was useless. Tessie de Mothay, at Metz, obtained moderately good results with the process, but Albert, of Munich, was the first who succeeded in making it of any practical importance.
Albert Process : " Lichtdrucke." — All experimenters before Albert had transferred the gelatine film to metal, to which it only adhered imperfectly. Albert poured the gelatine solution of bichromate of potash in the dark, on glass, and, after drying, exposed it, glass upwards, for a short time to the light. In this way the light produced a superficial effect ; the part of the gelatine adhering to the glass became insoluble, and thus firmly fixed. A negative was then placed on the film and exposed to the light. A faint greenish picture was thus produced. The exposed film was then washed in water until all the bichromate was removed, and then was suffered to dry.
To print from such a film, it was first rubbed with a sponge wetted with a dilute solution of glycerine. Those parts only of the film which were unaffected by light absorbed the water. A leathern roller was inked by rolling it on a slab of marble on which printer's ink had been spread, and then lightly passed several times over the gelatine film. All places which had been affected by the light retained ink from the roller, but not so the others, and finally a well-defined picture appeared on the originally almost colourless surface. As soon as it had been sufficiently inked, a piece of paper was laid upon it, and passed through rollers coated with india-rubber, the plate being laid on a sheet of the same material. In this manner the ink of the picture passed over to the paper, and produced thus an impression with all half-tones. The inking and printing could be repeated at option, and thus thousands of copies prepared if the plate was very firm.