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Bookplate of unknown year, but the artist, H. C. Bärenholdt, passed away in 1976. Source.

Masaji Yoshida Bookplate 1965-01-01 Japanese Bookplate Collection

Ex-libris by the Catalan artist Alexandre de Riquer (1856-1920), made around the year 1900. These ones are some of the examples preserved in the National Art Museum of Catalonia (MNAC).

An ex-libris, also called bookplate, is a kind of printed stamp at the beginning or end of a book that says who owns it (think of the stamp you surely have seen in the books owned by a library). Though ex-libris have been used since ancient times, their "golden age" in Catalonia was during the Modernist movement (the Catalan equivalent of Art Nouveau), where many bookworm people commissioned artists to have a beautiful personal ex-libris that they could use to stamp all their collection.

The text in the 1st one, written in the Catalan language, says "no matter how much you know, there's always much more that you don't know" (per molt que sapies es molt mes lo que ignores).