Ref to my original post 7/10/03.
Found explanation of the process in ME V60 Issue 1452 p232 viz:
"Draughtsman's blue prints are produced in a similar way to prints
from photographic negatives. The drawing should be on clear tracing
paper, in fact, it is a tracing from the original drawing. The lines,
figures & letters should be bold & black. The tracing is placed behind
glass in a printing frame & behind it is placed the printing paper. If
you will examine an ordinary photographic printing frame you will see
the idea. The glass side of the frame is then exposed to light for a
period which must be found by experience. With summer sunshine about
ten minutes to twenty minutes will usually suffice, in winter one hour
or more may be necessary.
Continue the exposure until all detail on the printing paper has
disappeared or approximately so. Then remove the sheet of printing
paper & wash it thoroughly in running water & leave it in water a few
minutes. The drawing will then appear in white lines on a blue
background. The paper is known as ferro-prussiate printing paper . .
Thank goodness for copiers & printers.
Norfolk - UK
- posted 18 years ago