'Policy of Pledges', September 1832. Newcastle is depicted binding and gagging his MPs in the name of 'Tory interests'.
Examples of satirical caricatures against the fourth duke (especially relating to his politics) may be found in:
H T Dickinson (editor), Caricatures and the Constitution, 1760-1832 (1986), Plates 122, 126, 133, 140 and 148.
The collection held in the Department of Prints and Drawings, British Museum, is extensively described in M D George, A Catalogue of Prints and Drawings in the British Museum, Division 2: Political and Personal Satires, Volume 11 (1954).
The Newcastle family portraits were deposited at the University of Nottingham in 1990. An exhibition marking their arrival was held in 1992 and an illustrated catalogue (together with scholarly commentary) was published to mark the occasion. See Joanne Wright (editor), The Newcastles of Clumber: a pictorial and documentary history of an important Nottinghamshire family (1992).
For an indication of the fourth duke’s artistic tastes and collecting habits, see the various catalogues drawn up for the sale of Clumber's effects in the 1930s held in the University of Nottingham East Midlands Collection. These are listed at http://aleph.nottingham.ac.uk/ALEPH (search under 'Dukes of Newcastle' and ‘Clumber’).
Philip Jones, The Dukeries: Clumber, Rufford, Welbeck, Thoresby and Worksop Manor on old picture postcards (1993) provides useful illustrations of two estates with which the fourth duke had close connections – Clumber and Worksop.