Berthelsen's career is the unusual story of a working musician who became a working painter in middle age, an immigrant operatic tenor who, when economic circumstances closed the singing studio, opened the painting studio and produced one of the most affectionate visual records of mid-century New York.
Berthelsen came to art from one art form to another. The Copenhagen household in which he was born was, by the family's account, supportive of all the arts, and his early training in the United States was musical: a conservatory graduation launched a fifteen-year career as an operatic and concert tenor, and his later decade and a half of conservatory teaching placed him among the leading American voice teachers of his generation.
His turn to painting was at first an avocation. Encouraged by Svendsen, whose Impressionist snow scenes he particularly admired, and by his friendship with Adams, a portraitist who had studied directly with William Merritt Chase and Robert Henri, Berthelsen began painting in his free hours. The example of Svendsen's snow paintings provided the immediate visual model for what would become his own signature subject; the friendship with Adams gave him a working artistic interlocutor of his own age.
The Depression rearranged his life. The 1929 collapse of his voice-teaching practice left him without his primary income, and what had been an avocation became a necessity. The family moved to New York and Berthelsen set up a painting studio in the city, where he began working in oils and selling his canvases through the growing market for Impressionist American landscape and cityscape painting.
The body of work he produced from the 1930s through the 1960s is the cohesive, recognizable record of a subject he returned to almost exclusively. New York under snow, New York at dusk, the lit windows of brownstones and the lamp-haloed figures on winter avenues, the Plaza Hotel and Madison Square seen through falling flakes, the paintings work a particular slice of Manhattan in particular weather and light, repeatedly and with considerable feeling. The handling is loose, the palette restrained and tonal, and the atmosphere unmistakable.
His paintings entered both major institutional and high-profile private collections during his lifetime and have continued to circulate through the postwar American art market in the decades since his death. His position today is that of a beloved chronicler of mid-twentieth-century New York, an Impressionist working in a tradition that had largely been overtaken by mid-century modernism, but whose particular subject and sensibility have given his work a steady audience that crosses both regional and national American collecting