The Americans call concertinas accordions. So since this is a woven accordion from the 100 books book (my current bible), then it’s really a woven concertina.
Used my old postcards (mostly addressed to me, but some to a few others in my network: former flatmates, my sister, my ex-husband…).
Decorated the backs with stamps, partly because it protects what privacy there ever is in a postcard, partly because the backs didn’t look interesting enough (and now they look more interesting than the sterile postcards do!).