By hello
Ultramarine emphasis. The apron’s intense blue is one of the painting’s dominant color events. Vermeer is famous for using costly natural ultramarine in major works, and the apron helps bind the lower half of the composition to the blue jug and sleeves. Its heavy folds also make the maid’s body feel weighty and sculptural, reinforcing the Rijksmuseum’s description of her statue-like presence. References: Rijksmuseum collection record; Metropolitan Museum of Art essay; standard Vermeer pigment scholarship summarized in museum literature.