โ Scribed by John Carbutt
No coin nor oath required. For personal study only.
The Secretary having desired me to describe to the members of the Franklhl Institute how 1)hotographs in printing ink are made; before doing so pernfit me to read from an article prepared by me a short thue since fbr one of our journals--" Tile Photographic :Rays of Light. '~ in 1796 Alols Senefelder, of ~Iunich, a musician and composer, was in the habit of using pieces of slate of limeston% on which to arrange his compositions before putting them on paper.
While so engaged he wrote with pencil, on a piece of this stone, a memorandum for h~s mother. Accidentally it fell into a vessel containlng greasy water ; to his astonishment he saw that every letter had become coated with grease contained in the water, and without affecting the other parts of the stone. This simple accident led him to the discovery of lithography, and little did he dream at that time of the marvelous results now obtained throughthe means of his invention, or that a chemically prepared surface would be discovered on which, by the action of llght, natural object.s, portraits and works of design and construction would be drawn, which, when placed in the printing press, would yield, by a process of printing strictly analogous to his own~i copies of ~uch objects in permanent pigments.
In 1839 M:ungo Ponton, of England, discovered that when paper coated with a solution of biehromate of potassiUm~ and after drying w'ts exposed to light under a drawing, that it received an image, of a brown color, to preserve which it was only necessary to wash the paper in water to remove the bichromate not acted upon bythe light. This, as f'tr as known, is the first instance of a picture having been produced by the action of light on a body impregnated with a bichr0mate salt,
In 1854 Paul Pretsch made knmvn his discovery that a film of gelathm and bichromate of potassium, after exposure under a drawing or other design to light, and after damping with water, would receive ink fl'om a roller passed over its surface where the light had acted upon it, and refuse it where the light had not acted, owing to those parts hav-
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author covers subjects such as latent image theory, the mechanism of development, reciprocity failure and color masking. The serious photographer will welcome this complete treatise on the subject.