03:45Snapshots in the DarkJulia Margaret Cameron: Portrait of Thomas Carlyle, 1867BBC Radio 4 Extra Duration: 15 minutes Mon 24th Apr 2017, 03:45 on BBC Radio 4 ExtraColin Ford discovers how Cameron changed portraiture forever, thanks to her life-size reproduction of the head. From December 1999.GenresFactualArts, Culture & the MediaSeriesSnapshots in the Dark Source: BBC Online