The collector that owned this coffee cup had taken it to the Worcester Porcelain Museum where the attribution to James Rogers was made. www.worcesterporcelainmuseum.org.uk/
James Rogers Porcelain Painter :
This man is rather mysterious, little is known of his life and attribution of his work is very difficult. The only documentary evidence is that a James Rogers was working in London in 1765 as an `Engraver Enameller` at Dobson China Shop in St.Martin`s Court but is he the same man as the Worcester enameller I. (or J) Rogers ? A Worcester porcelain mug in the British Museum appears to be the only clear link between between the work and the name of the artist. The base has a painted inscription “I. Rogers, Pinxit, 1757”. The mug is decorated with birds of a type referred to as Mobbing Birds. Other pieces have been attributed to him on the strength of comparisons with this mug, most of the objects are decorated with Mobbing Birds inspired by prints including ones from `The Ladies` Amusement` of c.1760. It must be noted that there were many other English decorators working in this European style at the time.