Lady with an Ermine

 

A portrait of Cecilia Gallerani who was the mistress of Ludovico Sforza, Duke of Milan. Leonardo was probaly in the service of the Duke when this was painted. The ermine is though to symbolize purity.  Leonardo said about the ermine:

"Moderation:The ermine out of moderation never eats but once a day, and it would rather let itself be captured by hunters than take refuge in a dirty lair, in order not to stain its purity." and "Moderation curbs all the vices. The ermine prefers to die rather than soil itself."

"The association of the ermine with Cecilia Gallerani could have been intended to refer both to her purity and to make an association with her lover. Alternatively, the ermine could be a pun on her name because the Ancient Greek term for ermine, or other weasel-like species of animals, is galê (γαλῆ) or galeê (γαλέη)" 

The Lady with an Ermine has been subjected to two detailed laboratory examinations. The first was in the Warsaw Laboratories, the findings being published by K. Kwiatkowski in 1955. The painting underwent examination and restoration again in 1992, at the Washington National Gallery Laboratories under the supervision of David Bull.[11]

The painting is in oil on a thin walnut wood panel, about 4–5 millimetres (0.16–0.20 in) thick, prepared with a layer of white gesso and a layer of brownish underpaint.[11] The panel is in good condition apart from a break to the upper left side of the painting. Its size has never been altered, as indicated by a narrow unpainted strip on all four sides of the painting.

The background was thinly overpainted with unmodulated black, probably between 1830 and 1870, when the damaged corner was restored. Eugène Delacroix was suggested to have painted the background. Its previous colour was a bluish grey.[11] The signature "LEONARD D'AWINCI" (which is Polish phonetical transcription of the name "da Vinci") in the upper left corner is not original.[12]

X-ray and microscopic analysis have revealed the charcoal-pounced outline of the pricked preparatory drawing on the prepared undersurface, a technique Leonardo learned in the studio of Verrocchio.[13]

Apart from the black of the background and some abrasion caused by cleaning, the painted surface reveals the painting is almost entirely by the artist's hand. There has been some slight retouching of her features in red, and the edge of the veil in ochre. Some scholars believe there also was some later retouching of the hands.[11]

Leonardo's fingerprints have been found in the surface of the paint, indicating he used his fingers to blend his delicate brushstrokes.[14]

-Wikipedia 

Leonardo Da Vinci 'painted three Ermine portraits'

A French scientist has revealed a major new discovery about one of Leonardo da Vinci's most famous paintings, shedding new light on his techniques.