printing frame the results are sometimes unsatisfactory, and now that
the process has come to be so commonly used I have thought that an
account of an inexpensive but efficient printing frame would be of
interest. The essential parts of the apparatus are its frame, its glass,
its pad or cushion, its clamps, and the mechanism by which the surface
of the glass can easily be made to take a position that is square with
the direction of the sun's rays.

_The Blue Process Printing Frame in Common Use.--Its Defects._--The pad
of the apparatus in common use consists of several thicknesses of
blanketing stretched upon a back board. The sensitized paper and the
negative are placed between the pad and the plate glass, and the whole
is squeezed together by pressure applied at the periphery of the glass
and of the back-board. Both the glass and the back-board spring under
the pressure, and it results that the sensitized paper is not so
severely pressed against the negative near the center of the glass as it
is near the edges. If at any point the sensitized paper is not pressed
hard up against the negative, a bluish tinge will appear where a white
line or surface was expected. With an efficient printing frame and
suitable negatives, these blue lines will never appear, and it was to
prevent the production of defective work that I undertook to improve the
pad of the printing frame.

_The Printing Frame Used in Ordinary Photography._--Very naturally, I
first examined the printing frame used in ordinary photography. This
frame is extremely simple, and is very well adapted to its use. It is,
undoubtedly, the best frame for blue process printing, when the area of
the glass is not too large. The glass is set in an ordinary wooden
frame, while the back-board is stiff and divided into two parts. A flat,
bow-shaped spring is attached by a pivot to the center of each half of