Exposure to light of the photosensitive gelatin

Châssis à insoler U.V.
Châssis à insoler U.V.
  • GENERAL INFORMATION ON EXPOSURE TO LIGHT : While the gelatin/dichromate/water has not been dried, ultraviolet light has no effect on the gelatin. The action takes place only when it is completely dry and only with Ultraviolet light. It is thus the U.V. of the natural light that make sensitive the gelatin when we choose to insoler the plate in the light of dayt. At present, use is made of tubes or lamps high pressure mercury vapor, which is the spectral emission in the UV range
    Note that a light overexposure is preferable in an underexposure. At the end of the sunstroke, the positive image must be drawn on the plate, of a light yellowish brown darker than the yellow of the parts not affected by the light – any slightest details must be readable. However, the sunstroke must not be pushed until obtain the equivalent of a positive movie. The whites of the image do not have to undergo of significant modification of tint. With the use of lamps with ultraviolet spectre (tubes U.V. or lamps pressure of vapor of mercury) the time is generally returned to a duration varying from 4 till 15 minutes, according to the luminous intensity, the distance between the light source and the bichromatée gelatin, the concentration bichromate, the transparency of the movie, etc…. It is thus necessary to understandt hat tries are necessary to adjust according to the set up device.
  • EXPOSURE HAS THE NATURAL LIGHT : for the record – Consult the old works. Formerly, when it was made use of negatives on glass, the set was placed and pressed in a wooden frame before being exposed to the light natural. It is about the sunstroke in U.V. contained in the natural day light – process which was however appropriate during for a very long time before exist the ultraviolet lamps. Nevertheless, this method can be again used to make tries of sunstroke if we do not possess a lamp U.V.. It works correctly, but time of exposure are more difficult to estimate exactly because the natural luminosity is never identical.
Châssis à insoler U.V.
Châssis à insoler U.V.
  • EXPOSURE HAS THE ARTIFICIAL LIGHT ( U.V). :
    After drying in the steam room, from its cooling, the bichromatée gelatin can be exposed under pictures (to use quickly plates, in the days which follow). The composition containing the photographic film must be placed in contact completed with the sensitive coat of the plate, photographic emulsion if possible in touch with the bichromatée gelatin. The space must be made in the frame to perfect contact, what avoids obtaining diffuse images.