After Justus Engelhardt Kuhn, American, 18th century, a pair of oil paintings on canvas depicting portraits of Felix Mumenthaler and Anna Maria Mumenthaler, 1816. Inscribed to the back. Justus Engelhardt Kuhn was a portrait painter active in colonial Maryland in the early part of the 18th century. He was the earliest professional artist to work in the Middle Atlantic colonies. Antique Portrait Paintings For Collectors.