Light masking effects of polyester film

Elizabeth Hadlow <ehadlow [at] anmm__gov__au> writes

>We have noted several instances over the past couple of years where
>paper artefacts mounted with Mylar corners and strips have
>differential fading of the ink and/or discolouration of the paper.
>The area under the Mylar polyester film appears to be protected from
>light damage.
>...
>... We are interested to know
>whether other people have discovered similar effects? Or whether
>anyone can suggest the reason why this might be happening?

I have seen a similar protective affect on a 17th c book that had
been exhibited for about ten years at a Chicago museum. I do not
recall the type of lighting. The book had been strapped with a film
that appeared to be of a polyester type such as Mylar. While DuPont
Mylar Type D has some light filtering properties, I would suggest
that you have the film tested. You mig ht find that the film, if
indeed polyester, has been coated, and that the coating has changed
the optical properties. Unfortunately, in years past, when we have
ordered DuPont Mylar Type D, we might have received a substitute
film that was also clear. The bottom line is that we cannot assume
that a film is Mylar--it is not a generic term. As end users, we
should know that there are thousands of different types of polyester
film. We should also know specifically what type of film has been
delivered.

William Minter Bookbinding and Conservation, Inc.
4364 Woodbury Pike
Woodbury, PA   16695
814-793-4020
Fax: 814-793-4045


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                  Conservation DistList Instance 16:2
                  Distributed: Thursday, June 20, 2002
                        Message Id: cdl-16-2-002
                                  ***