Press′ure-frame.
（Photography.) Often called printing-frame and sometimes press. A strong shallow open frame of wood surrounding a square of thick plate-glass which rests upon a rabbet. When a positive “print” on sensitive paper is to be made from a photographic negative, the latter is laid with the collodion side upward upon the plate-glass front above described. A sheet of sensitized chloride of silver paper is then pressed into close contact with the negative, by a number of strong springs attached to hinged pieces which lock across the back of the frame, acting upon a movable wooden back separated from the sheet by suitable soft packing. When such a frame is turned up with its plate-glass side toward the sun, the light passing through the negative darkens the paper behind, so as to produce the positive picture or “print.” The wooden back upon which the springs act is divided into two parts, which are hinged together. By means of this expedient, it is possible to examine from time to time the progress made in printing, [1786] one half the back being raised while the other holds the paper firmly in place upon the negative, and to stop that operation when the shadows are sufficiently dark.
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| Pressure-gages. |
