No documents about A. A. Lamb or other paintings by him have been discovered. His sympathetic treatment of the subject of the National Gallery’s painting Emancipation Proclamation (1955.11.10) suggests he was a Northerner, perhaps from New York, where he could have known the Henry K. Brown statue of George Washington used as a model for the figure of Washington in the painting. The fancy shaded lettering on the chariot and that originally on the back of the canvas suggest experience as a sign-painter or decorator, perhaps of carriages. Details of the Capitol building in the painting indicate that the artist was active in 1864 or later. [This is an edited version of the artist’s biography published, or to be published, in the NGA Systematic Catalogue]
https://www.nga.gov/content/ngaweb/Collection/artist-info.1451.html