| Acetate-backed tapes (translucent when a reel is held to a light
bulb and viewed from a flat side) are from the '50s and '60s. The
water vapor they used as a plasticizer evaporates with time and many
have now become brittle.
They can be resuppelized by storing them in their boxes in a drawer or other closed humid environment for a six to nine month period without applying water directly to the tape.
I'm glad to inspect and identify which of your tapes are likely to yield to this process. I can then send them back to you so you can do this task at your end rather than have me charge you for doing it here.
Please be aware that this is precisely the wrong thing to do to plastic backed tape as exposure to moisture initiates or accelerates its breakdown.
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