engraving by Blake held in the collection of the University of Arizona Museum of Art. The engraving was for a book written by Blake's friend John Gabriel Stedman called The Narrative of a Five Years Expedition against the Revolted Negroes of Surinam (1796). It depicts three attractive women embracing one another. Black Africa and White Europe hold hands in a gesture of equality, as the barren earth blooms beneath their feet. Europe wears a string of pearls, while her sisters Africa and America are depicted wearing slave bracelets. Some scholars have speculated that the bracelets represent the "historical fact" of slavery in Africa and the Americas while the handclasp refer to Stedman's "ardent wish": "we only differ in color, but are certainly all created by the same Hand." Others have said it "expresses the climate of opinion in which the questions of color and slavery were, at that time, being considered, and which Blake's writings reflect". 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. Later life Blake's marriage to Catherine was close and devoted until his death. Blake taught Catherine to write, and she helped him colour his printed poems. Gilchrist refers to "stormy times" in the early years of the marriage. Some biographers have suggested that Blake tried to bring a concubine into the marriage bed in accordance with the beliefs of the more radical branches of the Swedenborgian Society, but other scholars have dismissed these theories as conjecture. In his Dictionary, Samuel Foster Damon suggests that Catherine may have had a stillborn daughter for which The Book of Thel is an elegy. That is how he rationalizes the Book's unusual ending, but notes that