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In today’s #thread we are going to talk about the analysis of organic binders used in the “secco” technique on fresco paintings at @pompeii_sites and #Herculaneum.
After the beginning of the excavations during the 18th century at @pompeii_sites and #Herculaneum, many chemists and archaeologists were amazed by the vividness of the mural paintings and tried to determine the painting technique. https://twitter.com/pompei79/status/1002144731252580354
The most abundant painting technique is fresco painting, characterised by the application of water-dispersed pigments on a fresh plaster, which finally carbonates and fixes the colours to the wall. https://twitter.com/Oskar_KimikArte/status/1115150537219919872
In a previous #thread, we have already mentioned how painters needed to work closely together at @pompeii_sites and #Herculaneum in order to finish fresco “giornate” in time before the carbonation of the plaster. https://twitter.com/cinnabarim/status/1264587203654672384
However, as we already explained in another #thread, some finer details, such as figure panels, seem to be executed over the fresco background using an organic binder https://twitter.com/cinnabarim/status/1325482624761155584
While inorganic components, such as calcite, are fairly stable, organic products used as binders tend to deteriorate much faster. Not only that, but past restorations have also contaminated the excavated mural paintings with waxes or other consolidants https://twitter.com/cinnabarim/status/1325482685490409473
On the other hand, since these binders are present in very low concentrations in the painting matrix, very efficient extraction processes are needed in order to detect all the organic components. …https://heritagesciencejournal.springeropen.com/articles/10.1186/s40494-019-0254-1
Fortunately, mural painting fragments of the House of the Golden Bracelet, the House of M. Fabius Rufus or the Villa Imperiale at @pompeii_sites, and the Villa of the Papyri at #Herculaneum have been subjected to organic binder analysis in the last years. https://twitter.com/CaterinaCategio/status/1054853680179175424
Before getting into all the scientific analyses, we all deserve to take a moment to appreciate –over and over again– how gorgeous the paintings of the House of the Golden Bracelet are. https://twitter.com/pompei79/status/1081607237624360960
While spectroscopic analysis is useful for inorganic components (mortar, pigments), specific instrumentation needs to be used to identify organic binders: liquid and gas chromatography, often coupled to mass spectrometry or other types of detectors.
Chromatographic techniques separate components of complex matrices, such as organic binders. Each compound can be detected based on different properties. In this example, different amino acids are distinguished thanks to their luminescence in samples of the H. of M. Fabius Rufus.
These samples ranged from the 1st to the 4th Pompeian styles and showed an interesting trend: 1st style samples contained more lipids and sugars, while the 3rd and 4th styles were richer in amino acids. This suggests a change in the binder used. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4240868/
Five fragments of the House of the Golden Bracelet were subjected to liquid and gas chromatography. Fragments 1 and 5 stood out for the abundance of glycine, indicative of collagen or animal glue. A mixture of animal or vegetal components could have been used in fragments 2 to 4.
Other samples of the same house and of the Villa of the Papyri reported the presence of vegetable compounds and wax, based on great quantities of hydrocarbons and salts of fatty acids and ketones compatible with those of plant cuticles.
https://onlinelibrary.wiley.com/doi/full/10.1111/j.1475-4754.2009.00478.x
https://onlinelibrary.wiley.com/doi/full/10.1111/j.1475-4754.2009.00478.x
Finally, in the fragments of Villa Imperiale a series of polysaccharides, amino acids compatible with those of cereals and fatty acids were detected, indicating the use of binder based on wheat flour, gums, and oils.
https://link.springer.com/article/10.1007/s00216-012-5746-8?shared-article-renderer
https://link.springer.com/article/10.1007/s00216-012-5746-8?shared-article-renderer
As we have explained throughout this #thread, the question on the organic binder of the “secco” technique has not been fully disclosed yet. However, we can confirm that Romans combined this technique with fresco painting on the walls of @pompeii_sites.
Aquí te cuento este #hilo en castellano: https://twitter.com/cinnabarim/status/1350852466074595330