Sample of a wrought-iron window grille designed by ornamental ironworkers in the 15th century.

Ornamental ironworkers learned their trades as apprentices, and upon finishing became members of the craft guild–a precursor to the craft unions of the 19th century.

Photo courtesy of the International Association of Bridge, Structural, Ornamental and Reinforcing Iron Workers.

See this image in the On High: Bridge, Structural and Ornamental Ironworkers exhibit.