Coggan is known from just one piece. The silhouette shows a woman, displayed in a pocket case, which is labelled ‘G.B. COGGAN/ARTIST’ in tooled gold text. The work is backed with wax, and has a fingerprinted base as well as dark shading in this area.
Source: McKechnie (Author of, British Silhouette Artists and their Work 1760-1860)
Coggan, G. B. (McKechnie Section 3)