Rosenberg’s portrait of Sonia Cohen, a former sweatshop worker and aspiring actress with whom he was in love, was painted during several sittings in May 1915 when Rosenberg transformed Sonia, then pregnant with her first child by fellow 'Whitechapel Boy', John Rodker, into a Whitechapel madonna. Rosenberg references Leonardo da Vinci’s The Virgin of the Rocks, where the Virgin wears a cloak of a similar blue, also fastened at the neck with a black brooch, and wrote to his patron Edward Marsh that he had ‘[…] done a lovely picture I’d like you to see. It’s a girl who sat for Da Vinci, and hasn’t changed a hair, since, in a deep blue gown against a dull crimson ground'. 'Portrait of Sonia' skilfully blends these references with more modern techniques. Rosenberg's paint handling is characterised by the strong, broad, vertical brushstrokes that dominate his portraits in this period, and he also employs a vivid crimson background reminiscent of Alfred Wolmark’s colourist work. The portrait shares both this background and treatment with Rosenberg's portrait of Clare Winsten (Clara Birnberg) (UCL), who married Whitechapel writer Stephen Winsten, probably painted in the same year, but with clearly a greater emotional distance between the artist and his subject than in his tender portrait of Sonia.