Charles Balthazar St Memin - portrait of William Poyntell

This miniature portrait was merely described at auction as, "Miniature Etching Of Distinguished Gentleman 19th Cent". Hence it was cheap.

However, it was immediately obvious as a Saint Memin portrait, being inscribed at the foot, "Drawn and Engr. by St. Memin, Philadd." see Charles Balthazar Julien Févret de Saint-Mémin - Wikipedia ...

With such engraved portraits it is usually possible to identify the sitter by reference to the book by Ellen G Miles which lists hundreds of examples with their images, see Saint-Mémin and the neoclassical profile portrait in America

One of the joys of collecting miniature portraits, although rarely possible, is to take an unidentified sitter and so to speak "bring them back to life". 

This one took a while to work through from the A's (thankfully his name was not Wyatt!), before being matched with a portrait of William Poyntell, who died in 1811 and was an eminent merchant and publisher. There is an extensive obituary for him in The Gentleman's Magazine, see The Gentleman's Magazine which opens:

"Sept 10 1811 Died at his house in Philadelphia, in his 56th year, universally lamented, William Poyntell, esq. late Merchant, and one of the Select Council of that city. He had retired from business several years having acquired an ample fortune, of which he merited the enjoyment by the most inflexible integrity in all his dealings and transactions with whomsoever he was engaged. Mr Poyntell was an Englishman, and his character holds forth so bright an example of usefulness and private worth, that we are persuaded we shall stand excused for entering upon it more at large. He was born at Chipping Norton in Oxfordshire, and baptized in the parish church there, April 9, 1756. ...."

He sold stationery and wall papers, there being a picture of scales sold by him at The Price of Freedom: Money Scales  and wallpaper at Stanley Y. Klos: Imlay Mansion There is a picture of his grave at  William Poyntell (1756 - 1811) - Find A Grave Memorial and discussion of his art collecting activities at  William Poyntell (1756–1811) - Springer and 'All my stained glass which I brought from Europe' ds 1500