Wright's "Air Pump" was unusual in that it depicted archetypes rather than specific people, though various models for the figures have been suggested. The young lovers may have been based on Thomas Coltman and Mary Barlow, friends of Wright's, whom he later painted in "Mr and Mrs Thomas Coltman" (also in the National Gallery) after their marriage in 1769; Erasmus Darwin has been suggested as the man timing the experiment on the left of the table, and John Warltire, whom Darwin had invited to help with some air pump experiments in real life, as the natural philosopher; but Wright never identified any of the subjects or suggested they were based on real people.