Ancient glue: how to remove it?

[Litargirio]

 

This image is of the underside of the keys of a 1965 accordion.

 

Basically, I am in need of removing the glue(?) or whatever it is that holding the wood onto the metal bars. I have gone and bought a professional glue remover that should be able to easily dissolve any kind of gluing material, yet it is having no effect on this.

 

I assume that whatever was used here 50 years ago is different from what we'd use nowadays, which is why my degluer isn't working.

 

Anyway, does anyone know what suff it is that was used here, and how to get rid of it?

 

Thanks in advance.

[HughMungusCynicalAnarch]

5 minutes ago, Litargirio said:

 

Either find either find an adhesives historian or take a sample and run it through a mass spectrometer.