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John, Hope this clarifies my question. I am trying to find out an explanation of the reason why, for sound base supports: light is more translucent if the tape is acetate (looking at the light passing thru the entire reel), and if the tape is polyester then it is less translucent; whereas with film the opposite appears to be the case - light is more translucent with a polyester base (also with the light passing thru the entire reel), and less so thru the acetate base. Lance Watsky Preservation & Media Specialist The Georgia Archives 5800 Jonesboro Road Morrow, GA 30260 678-364-3764 (phone) 678-364-3860 (fax) [log in to unmask] www.GeorgiaArchives.org -----Original Message----- From: Association for Recorded Sound Discussion List [mailto:[log in to unmask]]On Behalf Of John Ross Sent: Tuesday, March 01, 2005 12:47 PM To: [log in to unmask] Subject: Re: [ARSCLIST] Identifying Acetate Tapes 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 Seattle