Recent scholarship has underlined the importance of the practice of ‘extra- illustration’ or ‘grangerization’ in constructing antiquarian knowledge in the late Enlightenment: Thomas Pennant's Tours lent themselves particu- larly well to supplementary visual documentation of this kind. Extra-illus- tration in the late eighteenth century consisted of refurbishing a published text with an entirely new set of engraved prints, sketches, drawings and watercolours. The additional images were selected according to both per- sonal preference and to the subject of the book. They often took the form of engraved portrait heads, antiquities, maps, topographic views, heral- dic displays, newspaper clippings and even letters, and were occasionally supplemented with handwritten notes within the foot and margins of the page. The chosen images were inserted within the book alongside the cor- responding text; being either pasted in between pages of printed text, or rebound into separate volumes. Any type of book could lend itself to extra- illustration, from Shakespeare's works to antiquarian, topographical, and travel volumes. The suitability of Pennant's Tours through Britain and Europe for this type of personalization and embellishment lay in the fact that they contained numerous references to eminent individuals, antiqui- ties, monuments, landscapes, ethnologies and natural histories. Such wide- ranging subject matter allowed extra-illustrators a broad selection of topics on which to focus their attention.

Recent essays on Pennant's practice of extra-illustration by Paul Evans and Lucy Peltz have focused on Some Account of London (1790) and A Tour in Wales (1778–83), but Pennant's personal volumes of the Tours in Scotland, both 1769 and 1772, held in the National Library of Wales represent another fine exam- ple. These volumes contain original drawings by his ‘faithful servant’ Moses Griffith, as well as works by Paul Sandby, Adam de Cardonnel and John Clerk of Eldin, alongside numerous engravings taken from various publications. A hitherto little-known example by another hand is the extra-illustrated and annotated three-volume set of Pennant's Tours in Scotland in the collection of the University of Glasgow Library, made by the Dumfriesshire antiquarian Captain Robert Riddell of Glenriddell (1755–94) in the two or three years before his early death in 1794.