Today we are going to talk about the pink hues in mural paintings from @pompeii_sites. As we will see, their chemical characteristics make it difficult to be analysed in-situ. To overcome this, the pigments conserved at the Applied Research Laboratory have been of great help. 
This pink tone is to be found in certain examples at the Archaeological Park, frequently associated to the depiction of Venus, as in this painting of the House of the Venus in the Shell (Regio II, 3, 3).
In some cases, the pinkish hue is less astounding and often mixed with other tones, as in the grey elephants that are accompanying the goddess in this example of the Shop of Verecundus (Regio IX, 7, 6).
Another example would be this depiction of the sacrifice of Iphigenia by the seer Calchas, while Agamemnon refuses to watch and cries sitting next to a statue of Artemis. Found at the House of the Tragic Poet (Regio VI, 8, 3-5).
As we have mentioned in previous threads, several mural paintings from #Pompeii were executed according to Greek models. Thanks to Pliny, we know that Timanthes (4th century BCE) painted the same scene with a veiled Agamemnon to represent his grief.
Pink tones were obtained in two ways: either through a mixture of red ochre (hematite) and white calcite/dolomite or via pink lake pigments, which are prepared upon precipitation of an organic colorant upon an inorganic substrate.
Here you have a lovely example of the use of a pink lake pigment in the Al-Fayoum #mummyportraits, shared by @JoanneDyer_BM:
Both Pliny and Vitruvius mentioned that inorganic compounds, such as calcium carbonate or chalk were dyed with red/pink/purple cloth, previously dyed with organic colorants (alizarin, purpurin) obtained from madder roots or Tyrian shellfish.
These organic molecules do not yield a noticeable Raman response using this portable spectroscopic technique, which is indeed useful to identify red ochre. Thus, a sample pre-treatment is needed, which was tested with the pink lake pigments conserved in their original bowls.
Thanks to the use of silver nanoparticles, which enhance the intensity of the Raman signal, it was posible to obtain the characteristic spectra of the pigments, with alizarin and purpurin bands. This is known as SERS (Surface Enhanced Raman Spectroscopy).
These analyses have allowed us to propose that some of the pigments conserved at the Applied Research Laboratory were obtained with Rubia tinctorum, the cultivated species, whereas the examples with a greater abundance of purpurin could be related to the wild Rubia peregrina.
Additionally, these microphotographs of pink and purple lake pigments from #Pompeii reveal the occurrence of Egyptian blue grains (CaCuSi4O10) in one of them, which shows a purplish hue due to the mixture of both pink and blue tones.
As Pliny wrote, the best “purpurissum” was that of Puteoli, near #Pompeii, “made to absorb the colouring liquid of madder”. Additionally, the inorganic substrate of the Pompeian pigments has been proved to be a volcanic clay, hence of local origin. Probably Puteoli?
If you want to learn more about our research on pink (and purple) lake pigments at @pompeii_sites:
pubs.acs.org/doi/10.1021/ac…
link.springer.com/article/10.100…
pubs.acs.org/doi/10.1021/ac…
link.springer.com/article/10.100…
Aquí te cuento este hilo en castellano:
Another interesting read on "purpurissum", with the contribution of @R_Siddall:
academia.edu/10648129/Pompe…
academia.edu/10648129/Pompe…
