between two glass plates. The emulsion side of the foil
should face the original.
(b) Expose them to a strong source of light so that the light
passes first through the original copy. The light source
may be sunlight, a rigging of sunlamps, or an ultraviolet
p r i n t e r , Determine the correct exposure time by exposing
several strips of foil for varying lengths of time and then
developing them ( (2) below). If exposure is too short,
the foil will develop with a dark background. If exposure
is too long, the foil will be clear, but the image will be re-
duced to faint lines. Correct exposure should be just long
enough to clear the background without reducing the
strength of the image. If the exposure is well timed, de-
velopment time will be unimportant, because only the sen-
sitive salts, which have been protected from the light by
the original image, will react to the ammonia.
(2) Development.
(a) Obtain a receptacle, such as a wide-mouthed gallon jar, to
serve as an ammonia chamber. Cover the bottom of the
jar with a piece of blotter or other absorbent material.
(b) Pour a few drops of strong ammonia solution into the jar,
and cover the jar with the lid. Ammonia fumes will fill
the jar.
(c) Curl the exposed foil around its shortest dimension. T h e n
quickly take the lid off the jar, insert the foil, and replace
the lid. Now observe the image as it develops within the
j a r . Remove it when it has developed to full intensity.
29. Reflex Printing
a. General An illustration on opaque paper or one that has writing
on the back can be transferred to Ozalid foil under room-light condi-
tions. The steps involved in the transfer are as follows:
(1) Preparation of a master copy by reproducing the illustration
on a translucent sheet.
(2) Transfer of the translucent image to Ozalid foil by contact
exposure and dry ammonia development.
b. Exposure.
(1) Place the illustration face up on a printing frame or sheet
of plate glass, and place the reflex medium (such as auto-
positive translucent paper or film) over the illustration, emul-
sion side down. The emulsion side may be distinguished by
its slight coloration and glossy surface. Film is used in pref-
erence to paper when delicate tones are required. Glossy
photographs, for example, are better reflected on film than on
p a p e r . Autopositive paper is less expensive than film and
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