This is "A Female Saint" painted in the Italian north by Pietro Lorenzetti, a renowned artist from the 14th century. This fragment of fresco once formed part of the border decoration of a large wall painting in the chapter house of San Francesco, Siena.
As you can see, the figure's pose – she recoils in fear, drawing her hand to her breast – is similar to images of the Virgin receiving the news that she would bear the Son of God at the Annunciation. Traces of paint reveal that the draperies were originally blue.
The brown-ish yellow lines we can see are called sinopia– these show the initial design or drawing of the fresco. Small traces of green-blue paint, probably a pigment known as azurite, revealing that her robes were originally blue.
This piece is an example of the work of Pietro Lorenzetti and his brother Ambrogio, who decorated several important religious and public buildings in Siena with frescoes. This fragment was removed in the 19th century and purchased by the archaeologist Sir Austen Henry Layard, a member of the Arundel Society founded to document and preserve Italian frescoes.
Note the stepped and curved outline framing the figure, which suggests that she was part of a border consisting of figures placed within decorative shapes.
A Female Saint hangs in The National Gallery on Trafalgar Square, London — free to enter. Point your phone at any artwork there and audioguide.london plays a free audio guide in six languages — no app download needed.