http://books.google.com/books?id=qAKOtKVFxyAC&pg=PA137&lpg=PA137&dq=painting+from+memory&source=bl&ots=J5AR0tHD5U&sig=ktEuIaW226oRIVOeQLEPmjpWT1g&hl=e

"...then he should turn his back upon the whole and paint from memory he will be in a better position to say something vital about his subject than the man who must always have his 'model.'"