The paper, without having undergone any preceding preparation,
except that of having been excluded from the light for several days,
is floated on a bath of the nitrate of uranium as follows:
Nitrate of uranium 2 drachms.
Distilled water 10 drachms.
The paper is left on the bath for four or five minutes, it is then
removed, hung up and dried in the dark room. So prepared, it can be
kept for a considerable time.
The exposure beneath a negative varies from one minute to several
minutes in the rays of the sun, and from a quarter of an hour to an
hour in diffused light. The image which is thus produced is not very
distinct, but comes out in strong contrast when developed as
follows: