The art world has recently been astonished (OK, “bemused and confused” might be a little more accurate) by a new claim emerging from the David Hockney / Secret Knowledge camp. Florentine art historian Roberta Lapucci has proposed not only that Caravaggio used lenses in a darkened basement room to project scenes onto his canvas (Hockney’s basic claim), but also that he applied a luminescent paste formed from crushed fireflies and white lead to the canvas to form a primitive kind of image fixing agent – a Renaissance precursor to what Hockney likes to call “chemical photography”.
Lapucci’s primary evidence is based on having found traces of “mercury salt” on some of Caravaggio’s canvases under X-ray fluorescence – yet she notes “That is not uncommon because it was used in glue, but we are awaiting proof he was using it on the surface, in his primer.”
Also, it has to be pointed out that Caravaggio’s lack of preliminary sketches is only correlative evidence, not causative proof: while I have yet to see any passage by Giovanni Battista Della Porta (presumably in his Natural Magic?) that discusses the firefly-based paste (allegedly used in 16th century drama productions). All of which would seem to indicate that Lapucci’s hypothesis is well worth testing: but without anything approaching a smoking gun as yet.
Poor old Caravaggio: for centuries, his reputation suffered at the hands of art historians, who were almost unanimous in their sneering dismissiveness. Yet opinion swung right around, and his powerfully-lit (if a bit overwrought, truth be told) artworks are now routinely described as masterpieces. To me, whether or not he used lenses and chemical trickery to assist him is almost a secondary issue: whatever means he happened to employ to fix his particular sense of pictorial drama onto his canvases were well worth it.
How would the presence of mercury salts indicate the use of fireflies? In Wiki’s article on fireflies:
http://en.wikipedia.org/wiki/Firefly#Light_production
“Light production in fireflies is due to a type of chemical reaction called bioluminescence. This process occurs in specialised light-emitting organs, usually on a firefly’s lower abdomen. The enzyme luciferase acts on luciferin, in the presence of magnesium ions, ATP (adenosene triphosphate), and oxygen to produce light.”
and luciferin doesn’t contain mercury, nor do luciferases, so far as I can tell. White lead doesn’t contain mercury either.
The presence of magnesium might mean something, though.
It’s a good question… like I say, though the hypothesis is worth pursuing, it’s hard not to see it as currently lacking a little bit of substance…