Update on Acceptance of Polyester Film Products for Use in Encapsulation of Paper Artifacts
Revised October 22, 2004)
Over the past several months, we have tested several biaxially oriented polyethylene terephthalate (PET) polyester films and found them to be satisfactory for use in encapsulation of paper artifacts. The acceptable films are:
- DuPont Teijin Films Melinex® film types 455, 456, 515, 516, made by DuPont Teijin Films (see http://www.dupontteijinfilms.com/ for international distributors)
- DuPont Teijin Films Mylar® type LJP181 and KL, made by DuPont Teijin Films (see http://www.dupontteijinfilms.com/ for international distributors)
- DuPont Hongji Films Type 8511 and Melinex®516, made by DuPont Hongji Films Foshan Co. Ltd., China
- Hostaphan® 43SM film, made by Mitsubishi Polyester Film, LLC, of Greer, SC 29652.
- KC Inc.'s films SH71S®, SKC SH72S® and SKC SH18S®. These films are available from a number of distributors.
- Tairlin CH28® film, manufactured by Nan Ya Plastics Corporation, Taipei, Taiwan, and available from Granwell Products, Inc., 185 Fairfield Avenue, West Caldwell, NJ 07039.
To the best of our knowledge, all of the tested films, with the exception of Melinex type KL and type KM films, are coated for slip on one or both sides for ease of handling. The two uncoated films are available in very small thicknesses, 92 gauge for Melinex® type KL and 48-200 gauge for type KM, which conservators may find limiting for many applications (100 gauge equals approximately 1 mil or one thousandth of an inch). While we would generally prefer uncoated stock to eliminate any chance of an unforeseen interaction with the artifacts being encapsulated, we do realize that most processors find slip coating to be essential for ease of handling. Moreover, most such coatings are highly stable.
While we have found the films mentioned above to be generally acceptable for use in paper conservation, the ultimate test for acceptability of any polyester film must be the ease and consistency with which these films can be sealed or joined with the equipment that is available to the individual user.
We are pleased to share information about product testing with the preservation community, with the understanding that information concerning favorable test results in no way implies product endorsement. Vendors are strictly prohibited by law from implying or claiming that the Library of Congress endorses any specific product, service, or material.
An essential cautionary note: Research in our laboratories has clearly shown that, over the long-term, encapsulation of papers without an alkaline reserve is likely to hasten their degradation. The real and immediate gain in protecting fragile paper from physical handling needs to be weighed against the equally real risk of faster aging. However, clear and practical solutions are available to conservators to avoid this balancing act. With the many options available for deacidification today, most papers can be deacidified before encapsulation. Where this option is not available or desirable for whatever reason, a sheet of alkaline paper inserted within the polyester envelope will also overcome the effects of trapped acids formed in the aging of paper, and actually help extend the life of the encapsulated artifact.