Turner 's work with his engravers has always been considered to be of special significance. Many hundreds of engravings were produced after Turner's work, chiefly by a small number of engravers whom Turner had effectively trained in the interpretation of his work by careful supervision. An engraving after Turner is not to be regarded as a reproduction in black and white line engraving of an existing watercolour; rather, Turner sought, by supervision of the engraving process, to achieve a multipliable black and white image possessing its own artistic unity, independent of the watercolour which formed the starting point. See Piggott, Turner's Vignettes; Lyles and Perkins, Colour into Line: Turner and the Art of Engraving; Herrmann, Turner Prints; and also Rawlinson, The Engraved Work of J.M.W. Turner.