Hi,
I would glue it with a clear paper glue, which is acetone-soluble and free of acid. Such a glue does not harm the metal, it can be removed without a trace, it does not disturbe the appearance of the coin, it does not corrode the metal or harm the
patina. I have
good experience with the
German "Uhu" brand. Note that coin glued this way remains fragile.
Things I would NOT do include: soldering; using ceramic glue as used for porcelain; using superglue
byzcoll
