[Illustration: A forgery of Egyptian limestone sculpture (RIGHT) compared with a genuine example of the type (LEFT). The forgery was proved so by analyzing the binding material of the color.] So far, the forgeries discussed have been substantially new constructions. This is to be expected when the motives of challenge to the past or self-vindication are at work; usually, however, the forger prefers to use a genuine piece, wholly or in part, as a starting point for his operations. This has none of the disadvantages of a copy; it avoids some of the difficulties of finding suitable materials; and it provides a pattern for such things as color, texture, and surface condition, in any changes or additions that the forger may make. One possibility is to construct a forgery with the aid of genuine fragments, or on the basis of a damaged original. Joseph Nollekens, the eighteenth-century English sculptor, who worked with Thomas Jenkins in Rome, himself tells of making extensive additions to pieces of Roman sculpture found as the result of excavation, which in due course went into famous collections in England. Similarly, Dossena sometimes used fragments of genuine _quattrocento_ work in his forgeries. This, too, was the method favored by Ioni for making his early Italian paintings. One great convenience of such procedures (for the forger) is that if suspicion is aroused and investigation made, it can always be alleged that the added work is merely honest restoration. Indeed, the line between restoration and forgery sometimes becomes blurred. Occasionally there appears in the art market a graft of a piece of one original onto another; its sellers would be consumed with indignation were it suggested that they had handled a forgery. The exploitation of genuine work, however, often takes much simpler forms than that described above. The signature of a master may be added to a school piece, or to anything that bears some superficial resemblances to his work; sometimes, indeed, the addition is to a work by the master himself, to convince the doubting and to increase its sale value. Not infrequently, however, there is present an inconvenient signature of the real author, which has to be obliterated or manipulated into something more attractive. A special form of manipulation is to put on some anonymous portrait a name which more or less fits the dress and character of the sitter, and so increases its sale value. Shakespeare and Milton are often so honored; and many mediocre portraits picked up in England have been adorned with the names of Colonial worthies, and thus found a ready market in the United States.