Hubert and Jan Van Eyck

In short, it is nothing but the careful and extremely skilful use of all the painter's resources which constitutes the so-called secret of the van Eycks. It makes their pictures precious not only on account of their appearance and finish, but as subtle recreations of those forms and places which they had to represent. This command of a pictorial language enables the artist to give real substance to abstract ideas and make them intelligible to all. - p. 9.