Spots inside bellows

[Bouleaux]

Hello,

My concertina (a Wheatstone Crane from 1937) has brown spots all along the inside of the bellows. Is this something I should be worried about? I can't smell anything I'd categorise as mouldy, but then again my sense of smell is a bit on the weaker side.

 

[d.elliott]

These are marks from having had damp/ condensation in the bellows at one time or another. It is quite common and nothing to worry about as long as those conditions no longer pertain. I would be more worried about the reeds, check there is no corrosion under the reed tongues as well as on top.

[Matt Heumann]

Brown marks on old paper such as the cardboard/fiber of bellows hinges are known as

foxing, are reddish-brown spots caused by oxidation of iron contaminants in the paper (less often by mold) from high humidity. While foxing generally does not threaten the structural integrity of the paper, it can be unsightly and reduce the value of collectibles such as documents or art. I agree with David, the reeds are what you need to check.