This is a graphite drawing on vellum by David Loggan, completed in 1676. The oval miniature shows Master Isaac Barrow—Cambridge mathematician, later professor of mathematics and master of Trinity College. You can see the detailed linework that defines his face and the books he holds. Loggan, an engraver from Danzig trained by Dutch masters, was a prolific plumbago artist. The piece was finished just before Barrow’s early death in 1677.
Isaac Barrow is in the collection of The National Portrait Gallery at St Martin's Place, London — free to enter. Point your phone at any artwork there and audioguide.london plays a free audio guide in six languages — no app download needed.