Framed set of French stamps

A set of two 90 cent French stamps in red ink matted and framed together; on the front is a portrait of Descartes looking out at the viewer with an open book in the background with the words "Discours sur la methode 1637" printed on the left page and the name "Descartes" printed below the book and a quill pen in an inkpot; other books are stacked behind him; in the border above his head is printed "Republique Francaise" and "Postes" vertically down the right side; the name "H. Cheffer" is printed below the lower right border.