There are comparable lead busts supposedly of Dr Salmon and his wife and another anonymous bust at the Victoria and Albert Museum.
The details of the dress (the embroidery of the waistcoats and the shape of the marble or stone socles on these busts is also instructive
Generally this type of bust is attributed to John Cheere (1709 -1787) who had the very successful yard at Hyde Park Corner from about 1738 and is now known for his works chiefly in lead and plaster.
The Anonymous Lead Bust in the V&A.
Note the stone socle - Square in plan but with the curved front panel.
This feature appears frequently in plaster busts by John Cheere.
Henry Cheere was believed to be the more talented sculptor of the two brothers, but I believe it is time for a reassessment.
It is my belief that much of the work signed by or attributed to Sir Henry Cheere was subcontracted.
An anonymous lead bust sold by auctioneers Fraysse, Paris, Lot 193, Summer 2012, probably by the same author of the V&A busts.
Lead portrait busts are in fact very rare - only a handful are known.
The busts of Dr Salmon and his wife at the V&A, I would say are by the same hand as this bust - they are ascribed to John Cheere - he certainly had the monopoly of this sort of sculpture in the mid 18th century.
The tradition that they are Dr Salmon and his wife is also slightly suspect -
It seems that Senesino owned a marble bust of himself and requested in his will that it be used as his funeral monument at Sienna. It has since disappeared, presumed destroyed in the Napoleonic Wars.