Construction blueprints


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We made Blueprints in college back in 1973.  The method was obsolete even then.  Invented in 1842, blueprints were truly Blue  The drawing to be copied, drawn on translucent paper, is placed against paper sensitized with a mixture of ferric ammonium citrate and potassium ferricyanide. The sensitized paper is then exposed to light.

Where the areas of the sensitized paper are not obscured by the drawing, the light makes the two chemicals react to form blue. The exposed paper is then washed in water. This produces a negative image, with the drawing appearing in white against a dark blue background.

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1 hour ago, Electromen said:

This produces a negative image, with the drawing appearing in white against a dark blue background.

 

Yeah, I've been wanting to print off a set in negative with blue background. When I did a takeoff on the ink required I changed my mind :lol:

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