Coming upon this painting in the exhibition, the viewer is confronted with an abrupt change from the other works. "The Girl with the Red Hat" is small even by Vermeer's standards; it is his only known work that was executed on wood panel; and most importantly, its immediacy and intimacy contrast sharply with the meditative mood of the other paintings.
Despite its modest dimensions, a strong visual impact results from the large scale of the girl. Brought close to the picture plane, she communicates directly with the viewer. Her direct gaze and slightly parted lips impart a sense of spontaneity and anticipation. Vermeer relies heavily on color to establish the mood of the work. The red of the hat and the blue of the robe contrast strongly with the muted background. The bright red of the hat advances, heightening the immediacy of the girl's glance, while the blue of the robe recedes, balancing the composition. Vermeer retained warmth in the robe by painting the blue over a reddish-brown ground. The materials - the red hat, robe and chair finials - are animated by highlights of reflected light. Subtle highlights on the girl's eye and mouth animate her expression. Finally, the intense white of the girl's cravat, painted as a thick impasto with parts later chipped off, cradles her face, focusing attention on her expression.
The small size of this work allowed Vermeer to use painstaking detail in its execution. A precise depiction of texture and light is achieved through the duplication of thin glazes over painted ground. To represent the hat, Vermeer firs painted an opaque layer of deep orange red. He then added semi-transparent strokes of light red and orange to render the feathers. The robe highlights allow the underlying blue to show through. With this glaze technique, the underlying layer is used to help model the forms of the composition.
Most scholars agree that Vermeer utilized a camera obscura in the composition and execution of "The Girl with a Red Hat". It is possible that he chose a wood panel support to replicate the gloss of a camera obscura image, which was normally projected onto glass. In particular, the diffused specular highlights of the lion head chair finial resemble the unfocused effect of an image seen in a camera obscura. Vermeer expert Arthur Wheelock points out, however, that Vermeer did not simply paint on top of an image projected by a camera obscura. While camera obscura effects were emulated in portions of the painting, in other places, the expected effects are not seen.
Compositional adjustments also contradict the literal reproduction of a camera obscura image. For instance, the left chair finial is larger and angled to the right. If the chair top is extended to the left, it ends up misaligned with the finial. Vermeer adjusted the lines of the chairback to stress the foreground plane of the composition while at the same time, allowing space for the girl's arm to rest.