Dutch master Johannes Vermeer painted his Girl Reading a Letter at an Open Window in the late 1650s. For about 250 years, it has been in the custody of the museum Gemäldegalerie Alte Meister in Dresden, Germany. We now know that the wall behind the girl has a large picture of Cupid! The existence of the painting within the painting was revealed by x-ray in 1979, but it wasn't known at the time whether Vermeer himself covered it up or not.
But when a major restoration project began in May 2017, conservators discovered that the paint on the wall in the background of the painting, covering the naked Cupid, had in fact been added by another person. When layers of varnish from the 19th century began to be removed from the painting, the conservators discovered that the “solubility properties” of the paint in the central section of the wall were different to those elsewhere in the painting.
Following further investigations, including tests in an archaeometry laboratory, it was discovered that layers of binding agent and a layer of dirt existed between the image of Cupid and the overpainting. The conservators concluded that several decades would have passed between the completion of one layer and the addition of the next and therefore concluded that Vermeer could not have painted over the Cupid himself.
The restoration is now complete, and the painting will soon go on exhibit. Read the saga of the hidden Cupid at The Art Newspaper. -via Kottke