Blue Print Frame
A blue print frame used to make copies of mechanical drawing. The process is done by exposing a sensitized paper in contact with the tracing paper to the light source in the frame. A chemical reaction takes place when washing with water to create a strong blue color, creating the image.
French, Thomas E A Manual of Engineering Drawing for Students and Draftsmen (New York, NY: McGraw-Hill, 1911)
Courtesy the private collection of Roy Winkelman