Sounds like a bit of fun chemistry here!  Assuming it really WAS
copper, I'd love to know the conditions during which the alleged
reaction took place.   I hope there was quite a bit of moisture around,
otherwise it's hard to see what could happen over the imagined time
period.

The copper ions would certainly inhibit all kinds of growth and may
have been added to the glue.  Or, brass or copper tacks may have been used
to hold the bellows material during glueing (or the leather bellows
material could have been part of an old sack used for storing potatoes
that had been treated with Bordeaux mixture).

Regards,
Paul Morris

P.S.  I just looked in a book to check the spelling of Bordeaux
and, would you believe it, Bordeaux mixture _is_ used to treat hides!
That'll teach me to be flippant on MMD!

 [ The traditional thick mixture of copper sulfate, slaked lime and
 [ water was originally sprinkled on grape vines to discourage thieves,
 [ and then it was discovered to be a good fungicide.  More about the
 [ classic 'bouillie bordelaise' (Bordeaux mush) at
 [   http://www.decanter.com/news/56970.html
 [
 [ Now I know why Bordeaux and all other wine is labeled "May contain
 [ sulfates"!  -- Robbie