[ARSCLIST] polyester or acetate?

["Gregorio G. Karman" <ggkarman@xxxxxxxxxxxxxxx>]

Dear list,

Due to a recent experience with an historical sound archive, I am trying
to get some insight into the details of aged magnetic tape and tape
preservation. I thought I had this right but now I am confused by the
description the literature does relating the methods that are used to
distinguish acetate from polyester tape. At first I had understood that
acetate is tranlucent when held agains the light, and here are some quotes
that support that:

"almost all post WWII acetate tapes, you can hold them up to the light and
see light through the edges of the tape pack."
<http://www.richardhess.com/notes/formats/magnetic-media/magnetic-tapes/a-base-film-primer/>
"
"All standard play, most long play, and some double play acetate
tapes have a translucent wind when held against a light source. This is
not the case with PVC or polyester tapes." quoted from a technical paper
found at <www.iasa-web.org>

however when I finally got to read what seems one of the most quoted
studies on the topic (IPI Storage Guide for Acetate Film) I found: