A quarter-plate photographic printing frame in which the whole of the picture can be examined at once can be made thus: Substitute for the usual hinged back of a half-plate frame a piece of |-in. board as shown in Fig. 1, sinking in it a recess A for the opal about § in. deep, or equal to the thickness of the opal to be used. The recess should be a little longer than the opal to allow room for the springs E and B, which clip the opal and hold it firmly. Two pegs are fixed at C and D to engage with holes in the frame and ensure accurate register. The back is held down by fold-over springs (see Fig. 2). By a method sometimes employed to prevent slipping, the back of the opal is touched with a composition of Canada balsam and wax.

Fig. I.

Fig. 2. How To make an Opal Printing Frame.