Digital BW, The Print

While we've been concerning ourselves with lightfastness to determine 
print longevity, it seems that room temperature and humidity are 
important factors to take into consideration.

The Image Permanence Institute at RIT has a simple calculator 
available for download, which factors in temp. and humidity.

http://www.rit.edu/~661www1/sub_pages/8page20.htm

Cheers,
Andre