It is common for museums to include in their collections management policies a schedule for the exhibition of light-sensitive objects such as works on paper and textiles. Frequently these policies include recommendations for light levels, and specify the length of time an object can be exhibited before it is returned to storage for a “rest.” The length of the exhibit period and of the rest time are actually purely arbitrary – in reality, all light-sensitive objects have a finite life span. Think of it as each object having a bank account from which you can make withdrawals, but to which you cannot make deposits. Each amount of time on exhibit is a withdrawal. The “rest” period is not a period in which the object recovers from its exhibit time, because – all together now – light damage is cumulative and irreversible. Once the account is gone, it’s gone. You simply have to tell anyone who asks you to shorten the rest time or lengthen the exhibition time that they are really asking you to spend the object’s life faster. Or, to look at it slightly differently, you can display the object frequently now, or you can display it seldom so that your great-great grandchildren might get a chance to see it.
As for how long this lifespan may be, that depends on many factors – your storage environment, the amount of light and other environmental factors in your exhibit space, and the fibers, dyes, inks and what have you that make up the object itself. Along with time spent on exhibit, these factors, both those you control and those you can’t control, will determine how long that bank account will last.
Anne T. Lane
Mountain Heritage Center
Western Carolina University
This post is also available in Italian, translated by Silvia Telmon.