Linecar & Stone, English Proof and Pattern Crown Size Pieces, Spink, 1968; North, J.J., English Hammered Coinage Vol. II, 3rd ed., 1991; Bateson, Coinage in Scotland; Manville & Robertson, British Numismatic Auction Catalogues 1710 -1984; together with twenty sale catalogues, mostly Spink Auctions; also a few photostats of relevant articles