Just remembered what was bugging me about that original article … way back in 2004 (and I thought I had blogged this, but perhaps it was in Explorator), a Berlin-based researcher had claimed to have figured out the ‘formula’ for Pompeii red, which included a pile of cinnabar. Discovery News had the story … here’s an excerpt:

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.

Clearly this is beyond my training, but I was under the impression that cinnabar would give a red colour ….

One thought on “Pompeii-Red-Was-Yellow-Followup

  1. I could be wrong, but this isn’t a terribly new idea– trying to find whatever textbook I first learnt it in, but the National Gallery of Art’s guide from their last Pompeii exhibit (back in 2008) definitely mentions the changes in color due to heat:

    Click to access LatinGuide.pdf

    I suspect it’s more that different kinds of red/light red would have reacted differently to heat stress, depending on the varying composition of the pigmentation. Presumably you wouldn’t have painted yellow on the same kind of yellow, and some of it must have been more red than not.

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