# blueprint photo?



## ferny (Feb 10, 2007)

I'm hunting around the interweb for ideas and came across this. I don't fully understand it right now, I've got a bad case of sleepy brain fog.

http://www.instructables.com/id/EDFPVXG9NIEQHO9YN9?ALLSTEPS


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## terri (Feb 10, 2007)

:scratch: Now, that is unusual. However, that end result is a lovely shade of purple-blue, so why don't you try it and post your results here?


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## Hertz van Rental (Feb 11, 2007)

Blueprints used to be used for copying technical drawings, notably for engineering and architectural work. Rather like an early Xerox.
The original process was invented by Herschel and utilised the reduction of FeIII to FeII by the action of light.
Processing was done with Potassium Ferricyanide to produce a complex blue salt.
The unexposed FeIII ions did not react whereas the reduced FeII ions did.
Modern blueprint papers use diazonium compounds combined with colour couplers.
The action of blue and low UV light  decomposes the exposed diazo compounds to produce a latent image. The unexposed diazo compounds are then made to react with the colour coupler by putting them in an alkaline atmosphere.
Windex contains ammonia and so will work as a developer.
The drawback with this non-silver imaging method is that it works on a one-to-one basis: one quantum of light absorbed results in one molecule of dye. 
In the silver based system the developer acts as an amplifier: one absorbed quantum of light results in around 1,000,000,000 molecules of image forming silver.
Exposures with blueprint paper are therefore very much longer than with silver based paper.
Some advantage can be gained by using light bulbs with a high UV/blue content for the contact exposure.


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