Oh nice - they have a book of John Singer Sargent's drawings/watercolours. There were a bunch of his watercolours on display here last year (I think at Dulwich gallery?) But I missed out on it.
It's fun to see stuff different to the slap-and-dash oil portraiture he's known for. It also seems to contain some details, with detailed write-ups about techniques etc.

https://books.google.co.uk/books?id=jM-JA2R8bMUC&printsec=frontcover&redir_esc=y#v=onepage&q&f=false