Blake employed intaglio engraving in his own work, such as for his "Illustrations of the Book of Job", completed just before his death. Most critical work has concentrated on Blake's relief etching as a technique because it is the most innovative aspect of his art, but a 2009 study drew attention to Blake's surviving plates, including those for the Book of Job: they demonstrate that he made frequent use of a technique known as "repoussage", a means of obliterating mistakes by hammering them out by hitting the back of the plate. Such techniques, typical of engraving work of the time, are very different from the much faster and fluid way of drawing on a plate that Blake employed for his relief etching, and indicates why the engravings took so long to complete.