Drawing Sun Prints - update

Hello all,
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
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"GeoffH @hotmail.com>" Details please?
Part A: Green Ferric Ammonium Citrate 250gms Water to make 1000cc
Part B: Potassium Ferricyanide 92gms Water to make 1000ccs.
For use - mix in equal parts and filter, just before use.
Apply by brush or sponge to one side of te paper. The paper is printed until the shadows bronze, and is the "developed" simply by soaking in one or two changes of fresh water.
If only the brown ferric ammonium citrate is available, then part A should contain 187 gms (not the 250 as for green), and part B should have 137gms of pot.ferri. instead of 92gms.
White titles can be written onto a blueprint with a solution of potassium oxalate dissolved as 170gms per 1000ccs of water.
The blue colour of prints can be improved by a final bath of 2.5% alum solution, 3% oxalic acid or 1% hydrochloric acid.
Overexposed prints may be reduced by bathing in 10% potassium bichromate solution.
This was taken from p.324 of the British Journal Photographic Alamanac 1950.
All these were perfectly normal chemicals used in photography, and WERE easily obtainable THEN, but may be difficult to find/get now. They should all be treated with just normal care, avoiding undue contact with skin and eyes, any splashes being washed off with fresh water immediately.
The mixed sensitising solution will not keep for long, and so is mixed just before use. The separate parts A and B should keep in good condition in well-filled bottles for a considerable time (months).
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