Pompeii, one of the most fascinating cities in Europe, famous for being frozen in time due to the eruption of Vesuvius, is once again teaching us. This time it’s about tiles. Here, heritage scientists have examined how various coloured tiles were created using methods that are as non-invasive as possible. The site is well known for its wonderfully preserved features, such as artworks and intricate mosaics, giving us a keen insight into the lives, styles, and interiors from individuals 2000 years ago. Two mosaics were chosen from The House of Gilded Cupids, a home once owned by a wealthy family in Pompeii.
As the works cannot be transported to a lab for investigation, portable instruments were used to carry out x-ray fluorescence and diffuse reflectance infrared Fourier transform spectroscopies (which help identify organic materials) to enable researchers to carry out an analysis of the elements used in their creation. The black tiles were found to have a composition typical of volcanic rock, containing aluminium, silicon, potassium, and iron identified from minerals such as leucite and diopside, which is unsurprising given the location.
The white tiles were found to contain mainly calcite, which may be the cause of the faster degradation of the white tiles due to a chemical reaction with gypsum from acidic rainwater. The calcite base was also true of the red and orange tiles. However, the colours were found to have higher levels of iron, indicating an additional layer of iron oxide mineral haematite was placed over the calcite to give a reddish hue.
This investigation is most impressive due to its non-invasive techniques. Previously an examination like this would have necessitated the destruction of the tile – such as cutting thin sections – but here the team used laser-induced breakdown spectroscopy (Libs) which enabled them to measure the depth of layers without interfering with the mosaic itself. These findings will help ensure the survival of these valuable insights into ancient history, and will enable researchers and conservationists to properly care for and restore the works.
For more information on the research visit © Iker Marcaida et al 2019
A new post by Hanna Simpson, Diary of a Tile Addict, April 2019