Although Southall was 30 years older than [Grant] Wood, there are many correspondences between their work, derived in part from their shared Quaker heritage which, among other things, led each of them to prefer to stand aside from the cultural centers of their respective countries – Wood in Cedar Rapids, Iowa, and Southall in Birmingham.... More important was their shared love and emulation of Renaissance portraiture, with its ruthless honesty and uncompromising directness of vision. In Southall’s case, this discipline was enhanced by his use of tempera, a demanding medium requiring great accuracy in the execution. This often gave his figures an air of frozen monumentality, as in The Agate. This somewhat disconcerting double portrait shows himself and his wife, Bessie, elegantly attired, collecting agates on the beach at Southwold, which she used for burnishing the gilded frames of her husband’s paintings. (https://www.apollo-magazine.com/modern-british-figurative-art-makes-a-comeback/