I’ve been working through some 60 year old BLUEprints updating the floor plans and materials for new construction on the original footprints. 2x4s were 1 5/8″ x 3 5/8″.
The blueprint process was invented in England in the 1840s, Tracing paper with black lines was sandwiched between glass with chemically treated paper and exposed to sunlight, creating a negative blue print with white lines.
The same basic operation was used over a hundred years with mechanical refinements and electric lighting. I still remember that chemical smell…
