A Roman wall painting of the first century AD, recently discovered in Rome,
has been studied extensively, in situ, by non-destructive X-ray fluorescen
ce (XRF) analysis. The coloured pigments, the medium and the plaster were a
ll examined. The presence of potassium and calcium in all coloured layers d
emonstrates that the painting technique is of a type very similar to that u
sed in Pompeian wall paintings, and described in the 1950s by Selim Augusti
. In this type of wall painting, the pigments were dissolved in a lime/soap
/water solution, the function of the soap being to mitigate the negative ef
fects of lime on alkali-sensitive mineral-based colours.