The urn-capped frame has laurel-festooned Roman acanthus husks corresponding to those of a pier-glass pattern featured in Robert and James Adam's, Works in Architecture, 1774, vol. II, pl. VIII (P. Ward-Jackson, English Furniture Designs of the Eighteenth Century, London, 1958, fig 229). Thomas Chippendale introduced festoons in his overmantel frame design for a painting at Nostell Priory, Yorkshire, while the base plinths with laurel-festooned patterae relate to an Adam design for Derby House, London.
A related urn-capped and festooned pier glass, with similar eared 'architectural' and volute-scrolled corners, also appeared in a Matthew Darly etching dated 1770 (ibid., fig. 257).
The ribbon-ties are very much in the manner of John Linnell as seen in his drawings at the Victoria and Albert Museum, London.