Complex sentence: George Jackson (1766--1840) was a male British plasterwork innovator active from 1780 onwards who was commissioned by architect Robert Adam to produce reverse-cut boxwood moulds (many of which to Adam designs).
Split into simpler sentences: George Jackson (1766--1840) was a British plasterwork innovator, active from 1780 onwards. He was commissioned by architect Robert Adam to produce reverse-cut boxwood moulds (many to Adam designs).