Nov. 1, 2004 — An Italian researcher has discovered the formula of Pompeian red, the shiny and intense color that dominated Pompeii's wall paintings 2,000 years ago.

Buried in the catastrophic eruption in 79 A.D., the brilliant red has been preserved forever by Mount Vesuvius's lava and still makes an impressive show of itself in several frescoes.

It abounds on the walls of the Villa of Mysteries — making the enigmatic pictorial cycle one of the most vibrant and intense of the ancient world.

"Though it consists of simple cinnabar pigment, Pompeian red is really unique. It certainly stands out when compared to normal cinnabar paint layers," Daniela Daniele, a researcher working at Berlin's Staatliche Museen, told Discovery News.

Aiming to discover the causes of the dramatically different chromatic effect resulting from the use of the same mineral pigment, Daniele analyzed the stratigraphies of some samples from Pompeian villas featuring the unique red and compared them to other ancient Roman wall paintings containing normal cinnabar paint layers.

Cinnabar is mercuric sulfide, the principal ore contained in mercury.

It emerged that in the case of Pompeian red, natural cinnabar was processed with particular care, which included what Daniele calls "purification, grinding and dimensional control."

"The finer the grains are, the more brilliant and covering the color is. But there is much more. In my microscope observations, I detected a bimodal granulometry with 10-15 micron crystals acting as shiny particles in a matrix of finer grains," Daniele said.

Basically, the ancient Romans simply added some bigger grains to the finely processed cinnabar powder, made of grains measuring about 2-3 microns. The result was a glittering surface that did not loose its saturated red tone.

According to Bernardo Marchese of Naples University Federico II's materials engineering department, cinnabar red required careful processing indeed.

"The pigment was used in lime medium, and had to be liquid enough to be applied in paint layers on the wall surface ... . The final result was subjected to wax polishing, in order to prevent alterations, especially when the color was applied on outside walls," Marchese and colleagues wrote in the catalogue of the Pompeii exhibit "Homo Faber: Nature, Science and Technology in a Roman Town."

Daniele's analysis showed that, on the contrary, samples of normal cinnabar paint layers featured just a light processing of the pigment. Cinnabar powder made of larger grains measuring between 10 and 25 microns turned out to be more transparent and dull, producing a color similar to a red ochre, the researcher said.

"It shows that Pompeian red is really special. It represents the height of the ancient Roman's mastery in making colors," Daniele said.