At  3/1/2005 09:28 AM, Lance Watsky wrote:
>Can anyone venture a guess, or actually knows, why light will pass thru
>acetate  audiotape and not polyester, whereas with film just the opposite
>is true, light will not pass thru acetate film, but will be able to shine
>thru the polyester film.

I'm somewhat confused by this discussion. It has been my experience that a
reel of acetate tape will indeed pass light on the wide axis of the reel
(with the light source more or less perpendicular to the center hole), but
light will not pass through a single layer of the same tape. This allowed
the automatic shutoff on the old Revox A77 to pass the tape between a light
and a photosensor.

As I have been reading the current thread, I'm not sure if the original
question or the replies were all talking about light passing through a reel
of tape.

Assuming we're talking about a reel of tape and not a single layer, I can
say that this phenomenon does not depend on the age of the tape -- I was
taught to use this technique to identify tape types in 1963, using new, or
used only once reels of tape at WGBH-FM.

John Ross
Northwest Folklife