“A printing frame that is well adapted to sheets not over 17 in. x 21 in. The frame is placed face downwards and the back A is removed by unhooking the brass spring clips B, B, and lifting it out. The tracing is laid on the glass C, with the inked side touching the glass. A sheet of the prepared paper, perfectly dry, is laid on the tracing with the yellow side downwards.” — Hallock, 1905. The painting frame is used to hold the original in contact with the light-sensitive paper in the blueprint reproduction process.
V. I. Hallock I.C.S. Refrence Library (Scranton: International Textbook Company, 1905)