sorry, the previous post didnt get through correctly, here the full version:
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, p 21) I found:
"When viewed "edge on" (holding the reel up to a light source and looking through the spokes of the reel), polyester film will transmit much more light than acetate or nitrate (see fig. 20). some light will pipe through the edges of the film with acetate, but polyester will look much brighter."
and fig. 20 shows 2 tapes, and the footnote says:
"When held up to a light source the polyester film "pipes" the light throught the edge of the film, while acetate and nitrate do not. (polyester film shown at right)"
and the tape of the right indeed lets more light through!
In my archive I found both translucent and opaque tapes but now I am confused.... any comments?
Thank you for your help
Gregorio Karman