Encapsulation

...
My understanding of the LC research was that unalkalized/unbuffered
materials backed with a sheet of buffered (permanent durable) paper
would be expected to age at the same rate that identical unencapsulated
material would age.  I don't recall that the article assessed the
possibility of accelerated aging of alkalized material over
unencapsulated identical material.  I would extrapolate from the (?still
primitive) research on the effect of bulk (as in textblocks) on paper
aging and the hypothesis that the byproducts of deterioration appear to
drive accelerated deterioration that encapsulation would be expected to
speed deterioration of anything, but you'd have to get a scientific
opinion from somebody like Chandru Shahani at the Library of Congress.

My own very limited experience suggests that encapsulation somehow
results in higher humidity inside the capsule.  At any rate, very
brittle paper I encapsulate as an example of the short-term advantage of
encapsulation for protecting fragile material from damage in necessary
handling appears to humidify over time inside the capsule.  At any rate,
it becomes noticeably more limp and flexible (relative to identical
unencapsulated sheets) over several months.  I have no explanation,
since I always encapsulate in my office, which is dry in winter and
air-conditioned in summer, and where my workshop samples ("controls")
are always stored.  Polyester is a semi-permeable material, but why
would the moisture transmission appear to go one way?   I don't know of
any conclusive research for this question.

Please remember that my observations are wholly subjective and
unscientific, but it's piqued my curiosity.  I would not recommend
encapsulation as a long-term storage strategy unless no alternative was
practical (as in very brittle pages under demand for access that have
been encapsulated and postbound).

Karen Motylewski
Northeast Document Conservation Center

                                  ***
                  Conservation DistList Instance 6:51
                  Distributed: Tuesday, March 23, 1993
                        Message Id: cdl-6-51-002
                                  ***