Blueprints & Blueline Prints fade rapidly with age, so don't leave blueprints (diazoprints) out in the air or under light for longer than necessary.
If you have old Blueprints (i.e., white lines on dark blue background) ask XPress Copy to make you a "reverse" (or "negative") copy, which will be much easier to read.
Because diazoprints are unstable (i.e, they fade), XPress advises you to scan important blueprints and bluelines to digital storage sooner than later.