Complex sentence: In 1771 Gardner won a silver medal at the Royal Academy of Arts and exhibited a portrait of an old man at the Academy of that year, but no further works were shown at the major London exhibitions.
Split into simpler sentences: In 1771 Gardner won a silver medal at the Royal Academy of Arts and exhibited a portrait of an old man at the Academy of that year. However, apart from this picture no further works by Gardner were shown at the major London exhibitions.