The Virgin in Prayer, Giovanni Battista Salvi da Sassoferrato
This beautiful painting is in the National Gallery, London, where is is currently part of their exhibition on painting materials, Making Color. This is primarily because of the artist’s use of genuine Ultramarine Blue in the robes.
Before the formulation of the modern synthetic version, French Ultramarine, in the 19th century, true Ultramarine Blue was made from the ground up semi-precious stone lapis lazuli, and was the most expensive of all pigments — more expensive ounce for ounce than gold.
Making Color is on exhibit at the National Gallery, London until 7 September 2014.
There is a high-resolution downloadable version of the image on Wikimedia Commons.