The draperyman was a specialist who assisted portrait painters in the 18th and 19th centuries in the design and rendering of costume accessories. Below: King George III in coronation robes by Allan Ramsay (1713–1784).
Draperymen had a knack for painting velvet, lace, satin, and silk, doing so in the style of their clients. Sometimes the portrait artist would paint only the head and hands and then send the canvas to the draperyman for finishing.
One of the most prominent among them was the Flemish-born Joseph van Aken, who assisted Allan Ramsay and Sir Joshua Reynolds. So much was van Aken depended upon, that after his death in 1749, William Hogarth made a satirical drawing showing his distressed clients dolefully following his coffin.
Draperyman at Encyclopedia.com