This is "A Muse (Calliope?)" painted in the Italian north by Cosimo Tura.
The painting shows a woman with a twisted, defensive pose, clutching an imaginary shield while displaying her luxurious sleeve. Six dolphin-like creatures, adorned with spikes and rubies for eyes, guard her throne. A scallop shell hangs from the throne, decorated with coral and crystal beads.
Calliope, the muse of poetry, is believed to be the subject of this painting. The branch of cherries may refer to justice, a principle associated with Calliope.
Technical analysis reveals that Tura painted over another design, possibly by Angelo da Siena, using oil paint over egg tempera on wood. This technique was not widely used in Italy at the time and suggests knowledge of Netherlandish art, particularly the work of Rogier van der Weyden. The flawless execution and use of translucent glazes to create depth of colour are characteristic of Tura's skillful application of oil paint.
This painting is one of nine Muses from a decorative scheme commissioned by Leonello d’Este, Duke of Ferrara, for his hunting retreat, Belfiore.
A Muse (Calliope?) 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.