a light-sensitive document of a lighthouse that is in the sunlight

Here is an extremely faded blue-line or diazo print of the New Presque Isle Lighthouse from a recent weekend trip. Blue-line or diazo prints are inexpensive copies of architectural drawings that were used from the 1880s-1930s.  Blue-lines are white with blue lines which are chemically unstable. You are probably more familiar with  Blueprints which are another form of chemically unstable architectural copies with a blue background and white lines. Both types of copies are chemically unstable because they are made with unstable chemical compositions.  In blue-line prints some of the chemicals are phenyl coupling agents-these oxidize over time causing discoloration and fading when exposed to air. [Thanks to Tawny Ryan Nelb for explaining this via her handy architectural records media/support and preservation chart!]  Exposure to light increases the speed of their deterioration resulting in rapid fading and loss of image. The speed of deterioration, fading, and becoming brittle also increases for blueprints when they are exposed to light. The rate of deterioration is so fast that if architects leave the room for lunch, leaving a coffee cup or pencil on top of an architectural drawing which is out on a table in room with lights on or sunlight, and the architects reappear an hour later and move the object, they will clearly see the image of the item they left setting on the blueprint during that hour.

In this case, this blueprint that was left too long in the sun. It is now exhibited in a room full of indirect sunlight, although it is not facing the window. This is not a good choice. A copy in the room would be better than having the original there on display to further speed its deterioration. I thought this being a light-sensitive document of a lighthouse that is in the sunlight would be an interesting Friday comment on archival architectural materials.


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