What can I use to remove the stains left on cardboard by scotch tape?
The tape was used 30-40 yrs ago, it has dried and fallen off, now
there are brown stains. The cardboard has a painted/printed design.

one thing you might want to try first is getting a peice of cardboard
as similar to the one you have as possible and some paint also similar
as possible and try different cleaning soloutions on it, ie windex,
tide, glass cleaner for tinted windows. and you might could use
"turtle wax polishing compound" its abrasive but it's a paste and
won't soak into the cardboard.

hope this helps

Chris Brown
President
Speedy's Cash Register, Inc.

Based on the value of the item, you should consider going to a
professional restorer.

WHile CRZYNDL-GA's suggestion to make a test mock up and try things
out on it first is good advice, the paint in used 30-40 years ago is
chemically very different from those in use today, also the adhesive
on the tape may be different and the aging over decades may be
significant to its susceptibility to solvants. You certainly do not
want to take the risk of using a solvant only to find out that it
didn't work on the tape.

good luck, I'd be very interested to see what worked.

J