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 backboard is stiff and divided into two parts. A flat, bow-shaped spring is attached by a pivot to the center of each half of the backboard. The two halves of the backboard are hinged together by ordinary butts. Four lugs are fastened to the back of the frame, and, when the backboard is placed in position, the springs may be swung around, parallel to the line of the hinges, and pressed under the lugs, so that the back of the backboard is pressed most severely at the center of each half, while the glass is prevented from springing away from the backboard by the resistance of the frame at its edges.

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