Dear Gregorio and all,
for my bachelor’s thesis, that I wrote within the framework of ILKAR
(Integrated solutions or Preservation, Archiving and Conservation of
Endangered Magnetic Tapes and Cylinders) at the Rathgen Research Laboratory
Berlin, I started to research the effects of heat treatment (baking) on
sticky tapes made of Polyesterurethane. I digitized my samples (back coated,
no given brand type or manufacturer) prior and after baking.
The audible squeal (first intermittedly, later persistently consistent, like
Joe describes it) manifested itself in the digifile as distortion with pairs
of peaking frequencies at eight and nine KHz, louder parts would show
distinct overtones at 16 and 18, as well as 26 and 28 KHz. So, in the file
the continuous squeal became a content-dependent distortion.
After baking (54°C, 15% rH,different treatment times), that distortion /
those peaks disappeared, so they were stickyness-related. The other effect
were heavy oxide losses after treatment.
The work is planned to be published in the near future, after it is graded.
Student of Conservation / Restoration of Audiovisual and Photographic Heritage
University of Applied Sciences, Berlin