Caution: Make registration cross marks at the four cor-
ners of the original before attaching it for tracing. Trace the
cross marks on the transparency when the drawing is trans-
ferred. The registration marks are particularly important
if partial tracings are to be made for the preparation of
used only in an authorized photographic laboratory.
28. Dry Ammonia Printing
a. General. Images drawn on tracing paper or photocopied on
translucent paper or film can be transferred to diazo-coated cellulose
acetate foil. Diazo-coated foils can be handled under ordinary room
lighting conditions. The following two procedures are required in
making transparent prints by the dry ammonia method :
(1) Contact exposure to a strong source of light, preferably
ultraviolet.
(2) Development of the exposed foil in contact with ammonia
vapor.
b. Printing Procedure Using Machine. Dry ammonia (Ozalid)
printing machines are motorized to convey diazo-coated materials
through exposure and development sections at controlled speeds.
Ozalid machines are designed to duplicate translucent originals rap-
idly on diazo-coated paper and may also be used for printing trans-
lucent tracings or other translucent masters on sensitive foil. P r o -
ceed as follows when using an ozalid machine-
(1) Place the original translucent tracing or photocopy on a sheet
of ozalid foil of the selected color so that the emulsion side of
the foil is in contact with the original.
(2) Hold the original material and the foil in contact, and insert
them into the light section of the machine so that the light
will pass first through the translucent original.
(3) Remove the pair from the light section of the machine, lay
the original aside, and place the exposed foil in a fold of ab-
sorbent paper (newspaper, for example). Then pass the
folded paper containing the foil through the ammonia cham-
ber of the machine, with the emulsion side facing the am-
monia vapor in the chamber. Pass the folded paper, with the
foil, through the ammcnia chamber again and again, if nec-
essary, until the image on the foil is developed to full density.
c. Printing by Hand. If transparencies must be produced without
an automatic printing machine, proceed as follows:
(1) Exposure.
(a) Place the original translucent copy in contact with a sheet
of Ozalid foil of the desired color, and hold them together
29
TAGO 4738B
