The plasterwork in the Great Hall was completed by Francesco Vassalli and his assistant Martino Quadri in 1731. They were both from Ticino, in Italian-speaking Switzerland. Vassalli is known to have worked at a number of English country houses such as Sutton Scarsdale in Derbyshire in 1724, Castle Howard in 1736-7 and Shugborough in Staffordshire in 1763. Comparisons with the work at Towneley have led to the attribution of plasterwork at several other houses in Lancashire to Vassalli.
The bill from Vassalli for the work at Towneley dated 1730 and the receipt signed for by Martino Quadri dated 1731 are still owned by the Towneley family and has been on display at Towneley several times in recent years.