An early discussion of UV filters is contained in a 1968 UNESCO
publication entitled: <The Conservation of Cultural Property>.
 
In that discussion UV filtering compounds in cellulose acetate films
"...should give 5-10 years' service in temperate countries."
 
In 1976, R.H. Lafontaine and K.J. Macleod, in: <CCI> the Journal of the
Canadian Conservation Institute, reported the results of "A Statistical
Surveyand the Use of Ultraviolet Filters in Canadian Museums, Archives
and Galleries."  Their report concludes with the statement that "There is
not much, if any, deterioration of these filters over time.  A more
extensive survey would be needed to determine if indeed there is slight
deterioration.  At any rate, museums can be reasonably confident of a
filter's effectiveness for at least 10 years."
 
Garry Thomson, writing in 1978 in: <The Museum Environment> asserts that
"The acrylic sheets seem to be of high permance, and can be expected to
last at least ten years, even in moderately exposed situations.  Foil and
varnish filters, to err of the safe side, should be regarded as having
the same sort of permance as the paint on the walls, and should therefore
be checked at not more than five-year intervals, using a UV monitor."
 
The long and short of it is that no-one seems to know for certain,
everyone repeats the early guess work, and only CCI seems to have put the
matter to a test.
 
Jack C. Thompson
Thompson Conservation Lab
Portland, OR
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