Johnson finished his formal schooling at fifteen and worked in a dry goods store where he began making drawings. Responding to his talent, his father sent him to work in a lithography shop in Boston, probably Bufford’s. Several figure and landscape sketches survive from the early 1840s which indicate the ways he was exploring the human figure and the landscape about him using graphite pencil. More importantly, he began to excel as a portrait draughtsman in these early years; see Themes 43.1–.9, U.S. Early Portrait Drawings.
Johnson's reason for his sojourn in Düsseldorf and The Hague, 1849–1855, was to learn to paint with oil (see Themes 1.0–5.0). To achieve that goal, he studied anatomy while still making graphite sketches of interiors, landscapes, and figures from life. Among his best composed sketches were those done on trips to the Dutch countryside, especially those done at Dongen, the Netherlands. —PH
Baur 1940, p. 31: "Johnson sailed for Düsseldorf with his friend, George Henry Hall, on July 15, 1849. The ship was the 'William Shakespeare' of the Dramatic Line, and the trip lasted sixty days to the mouth of the Scheldt." [Baur misstates the departure date, which actually was August 14, 1849.]