Uppsala's laser analysis finds an 18th-century blue in two patches of the 'L daVinci' Domitian

Raman spectroscopy identifies the compound in front of the laser, so a pigment dates a paint layer from one side only ^[2]. Prussian blue was first produced in the early 18th century, which makes it a floor: a layer containing it was applied after that date, and the layers beneath it are not dated by the finding at all ^[8]. Leonardo died in 1519, so the two passages carrying the blue went on at least 180 years after his death ^[17][23]. Twelve of the thirteen pigments were available in Leonardo's and Titian's time, which leaves one pigment carrying the whole dating result ^[5][24].

The laurel wreath is where the evidence is strongest, because two methods point at the same few square centimetres. X-ray imaging of the wreath shows several leaves that are visible on the painted surface and absent from the X-ray image ^[10], in one of the two areas where the blue appears ^[9]. That combination is what paint added over an existing composition looks like. "It is very common for paintings to be retouched. So, finding new pigments in limited areas does not necessarily mean that a painting is a forgery," Thyr said ^[11].

None of this touches the chronology that made the painting contested. Titian is believed to have painted 11 of the 12 Roman emperor portraits between 1536 and 1539, with the Domitian assigned to another hand ^[15]. The study's authors note that Leonardo died 17 to 20 years before that window, and they raise the possibility that the Domitian was finished first and inspired the rest of the series ^[17]. The series was reportedly sold from England to the Spanish Royal House and destroyed in a fire in 1734 ^[16].

The owners approached the Department of Materials Science and Engineering at Uppsala through Lars Hälldahl, who had worked with Thyr on similar analyses of artworks ^[21]. Both published accounts describe the material only as microscopically small samples taken from different parts of the painting ^[22]. The signature that started the argument is faint. "The contrast against the background is low, and it really only becomes visible when the painting is illuminated from the right angle," Thyr said ^[12].

Thyr expects more of this work. "Materials science analyses can provide concrete answers to questions about art and archaeological artifacts. I believe this type of analysis will become increasingly common in the future," he said ^[14].