Blueprints are a form of photoduplicate – which also includes methods like electrostatic duplicating, diazo, and photographic processes.It has white lines on a blue background of varying tones – the blue is a pigment called Prussian Blue. The support is usually paper, but can be drafting cloth.Blueprints often contain residual active organic acids, which may be detrimental to their long term stability.They fade when exposed to light, and this can happen very rapidly, although some prints react very slowly. A reversal of the fading may sometimes occur when the print is returned to dark storage, but this is not consistent so exposure to light must be kept to a minimum.Blueprints can also be sensitive to alkaline environments, so the usual archival alkaline buffered paper or board enclosures are normally avoided for packaging of blueprints. Neutral pH, unbuffered enclosures should be used, and encapsulation in an inert plastic film should be considered as a further barrier.There are many other kinds of architectural photoreproduction techniques which are too numerous to go into here – if you would like more information please let me know and I can point you in the direction of some good resources. You can also have a look at the Archives’ website which has preservation advice for this kind of material.
Preservation of Archive Materials by Prue McKay
Preservation of Archival Materials
Preservation Basics Session
2013 Community Heritage Grants