This form of shell-decked frame had been introduced in the 1720s by the Rome-trained architect James Gibbs (d.1754); while its ornament can be related to the George II 'picturesque' fashion promoted by G. Brunetti's, Sixty Different Sorts of ornaments very useful to painters, sculptors, stone-carvers, wood-carvers, silversmiths etc. , 1736-7 (see C. Gilbert, Furniture at Temple Newsam House and Lotherton Hall, Leeds, vol. III, 1998, No.810). In particular it relates to the 'ornament' of the celebrated carver Matthias Lock (d.1765), author of various pattern-books including Six Sconces, 1744.
The flower-festooned pier-glass has its octagon-compartment glass enwreathed by antique-fretted Roman acanthus that is tied by a flowered ribbon-guilloche and evokes the sun-deity Apollo's control of the Elements, as expressed by Collegit ut Spargat (the sun gathers clouds around it for their better dispersal). Sun-rays crown a Venus shell cartouche that nestles amongst reeds on the triumphal-arched, scalloped and wave-voluted trusses of its temple pediment; while its truss-scrolled pilasters are supported by water-dripped scallops rising from the base's assymetrical shell cartouche.