iece of blueprint paper under your waist or
coat, to keep it dark when you go into the light. Now lay it,
greenish side downward, on a negative. Hold the two together,
or place them in a printing frame, and turn them over so that
the light will shine through the negative upon the greenish
side of the blueprint paper. Be sure that the paper is held
firmly against the negative and not moved around. Let the sun
shine through the negative upon the paper for 1 or 2 minutes
according to the brightness of the sun, or let the gray light
of the sky, if it is cloudy, shine on it for 5 or 10 minutes.
Now quickly put the blueprint paper (not the negative) into a
basin of water, face down. Wash for a couple of minutes. Turn
it over and examine it. If it has been exposed to the light
too long, it will be dark; if it has been exposed too short
a time, it will be too light; in either case, if the print
is not clear, repeat with a fresh piece of blueprint paper,
altering the time of exposure to the sunlight to improve the
print.

You can make pretty outline pictures of leaves and pressed
flowers, or of lace, by laying these on the blueprint paper in
place of the negative and in other respects doing as directed
above.

[Illustration: FIGS. 174 and 175. Where the negative is dark, the print
is light.]

In making blueprints you are changing an iron salt instead of a silver
salt, by the action of light. Regular photographic prints are usually
made on paper treated with a silver salt rather than with iron salt,
and sometimes a gold or platinum salt is used. But these other salts
have to be washed off with chemicals since they do not come off in
water, as the unchanged part of the iron salt comes off when you fix
the blueprint paper in the water bath.

Since the light cannot get through the black part of a negative, the
coating on the paper behind that part is not affected and it stays
light colored; and since the light can get through the clear parts
of the negative, the coating on the paper back of those parts _is_
affected and becomes dark. Therefore, the print is "right side
out,"--there is a light place on the print for every white place on
the object photographed, and there is a dark place on the print for
every black place on the object.

Moving-picture films are printed from one film to another, just as you
printed from a negative to a piece of