Portrait of Mai by Joshua Reynolds, 1776 (ICP/Alamy)

Zoom in. The most unusual detail in this painting is the left hand, with tattooed dots carefully spaced across its back and knuckles. The fingers themselves are poorly done. The thumb and pointer are folded into the figure’s thick cloth folds, but the other three digits lie on the material like tapered slugs. Today they might be held up as evidence of AI image generation – bad hands are the quickest tell. In the eighteenth century, to the initiated, bad hands were a sign that the work came from the studio of Sir Joshua Reynolds.