Stephen,

A good, reasonably low relative humidity environment is what helps in
preventing mold and the photograph's surface sticking to the Mylar
(ferrotyping.)  For information, see NEDCC's website at www.nedcc.org ,
Section 4, Leaflet 11: "Storage Enclosures for Photographic Materials."

Alisa Vignalo
Field Services Coordinator
Upper Midwest Conservation Assoc.
612/870-3128

Stephen Linhart wrote:

> Hi -
>
> It's common knowledge to not place photos and documents on paper in
> contact with glass or plexi.  Yet with polyester encapsulation documents
> are placed in direct contact with the Mylar.
>
> Why is this ok?  Polyester film, such as Mylar, is permeable to moisture
> and there's also the recommended small gap in the seal.  So what protects
> against mold growing where the film meets the document, and what prevents
> transfer of image to the film?
>
> In short, why is it ok for Mylar to touch the document and not ok for
> Plexiglass?
>
> - Stephen Linhart