# Research on the Organic Binders in Archaeological Wall Paintings
## 4 Exploring Research Results
### Invasive Techniques  
One of the very first articles on the characterization of binding medium, conducted on samples taken from the wall painting, was carried out by [PERSON] [50]. In this work it has been proposed the use of thin layer chromatography for a preliminary recognition of unknown compounds, using standard reference substances. [PERSON] and [PERSON] have conducted studies on wall paintings paintings in Pompeii, taking samples, analyzed by means of preliminary FTIR spectroscopy analysis and TLC. They identified the presence of gums [51]. A stratigraphic evaluation of wall paintings could be achieved by preparing cross sections of the sample in resin and exposing them to UV-VIS investigation, before and after the application of specific stain examinations. In this way it is possible to identify the presence of organic constituents (specific classes of organic materials, i.e., proteins, lipids and gums) and their distribution in the layers [52; 53]. [PERSON] et al. (2016) have carried out a study, using Fourier transform infrared spectroscopy on thin sections of samples taken from prehistoric, Roman, Hellenistic and post-Byzantine wall paintings, in order to study the aging and the decay of organic binders and to understand the link with the formation of metal oxalates/carboxylates [54]. [PERSON] studied the organic components of grounds and pictorial layers in samples from central Asian and Crimean wall paintings. A first result allowed to see the presence of gelatin in mansur-deep wall paintings. In other 8 th century wall paintings, the use of the plant has been found, by investigation with infrared spectroscopy, polysaccharides attributed to the Prunodaee sub-family [55; 56]. [PERSON] studied the XII-XIII century wall paintings of [PERSON], in Georgia, dating to the 10 th and 11 th centuries. She found that gypsum plaster has animal glue and that pigments are laid out using egg yolk mixed with animal glue, using TLC, UV spectroscopy and electrophoresis to analyze samples [57]. The analytical research techniques that are presently most common in characterization of the organic media in mural paintings are infrared spectroscopy (FTIR), gas chromatography (GC-FID, GC-MS), pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), and high-performance liquid chromatography (HPLC). Interesting papers present overviews of the literature highlights that the analytical approach for use in GC-MS analysis of organic media in cultural heritage samples is strongly dependent on the specific problematic posed by conservators and art historians. The complex mixtures of molecular species present in organic materials, the requests to be answered, and consequently the analytes to be examined for, determine the choice of analytical approach, especially concerning sample pretreatment [58; 59]. A problem may arise when the extraction method used is not satisfactory for an ancient binding medium, then part of the binder may not be extracted, producing an incomplete characterization of its composition [8]. A very recent article addresses the problem of extraction of collagen-based binders (animal glue) in mural paintings. This work considered non-aged and aged samples and presents a comparative study on the extraction effects of six agents, used to extract the residual proteins. The protein extraction efficiencies of the selected agents were quantitatively determined by bicinchoninic acid method, and then processed by multivariate analysis of variance. The authors claim that, for both non-aged and aged samples, the extraction efficiency of 2 M guanidine hydrochloride was significantly higher than the other five agents, with less damage to the protein structure during the extraction procedure [60].