# Research on the Organic Binders in Archaeological Wall Paintings
## 3 Techniques and Procedures to Characterize the Organic Binders in Wall Paintings  
The characterization of organic materials in the wall paintings and their chemical-physical properties is fundamental for the knowledge of ancient paint techniques and for development of suitable conservation procedures. The Getty Conservation Institute (Los Angeles) developed an international data collection project (Organic Materials in Wall Paintings, OMWP) for the characterization of organic materials in wall paintings, by means of either non-invasive or micro-invasivetechniques. The study was based on the analyses of known composition replicas deriving from Affresco Workshop of Vainella (Centro Tintori, Prato, Italy), in which instrumental potentiality and limits in the characterization of organic materials in wall paintings were compared [14; 16]. Firstly, non-invasive techniques, which require the use of portable instruments for a general analysis in situ without sampling, can give information about the distribution of organic materials on the wall painting especially in the surface. Non-invasive methods represent a speed procedure to obtain general information about the composition of paintings, since they allow to acquire repeated measures in different points, by also identifying eventual regions contaminated by materials used in past restoration interventions. Moreover, the identification of the most significant regions can be helped by the use of imaging techniques and scan of the surface. In this way, it is possible also to select the most suitable points for sampling when a more in-depth investigation is required. Interpretative caution is always required in their use, as there is a risk of incomplete or partially distorted reading of data for certain component substances. In recent years, the various non-invasive techniques have been used in combination with each other to obtain a wide complete knowledge of the analyzed pictorial artifact. The characterization and the mapping of organic compounds is a challenge for the non-invasive technique of wall paintings. A wide range of non-invasive techniques are available, some of which can be summarized as follows [17]:  
* UV-induced fluorescence. Ultraviolet-induced fluorescence is an imaging technique that records visible light emitted from certain materials in the form of fluorescence when these materials are exposed to UV radiation. This technique allows to obtain information about the presence of fluorescent materials, i.e., colorants, varnishes, binders based on egg or oils, restoration products and any material which shows fluorescence after UV light excitation [18; 19]. Moreover, it is possible to use also portable multispectral imaging systems, which can identify the presence of fluorescent materials in wall paintings in relation to their multispectral properties [20]. * Time-resolved laser-induced fluorescence spectroscopy (TR-LIF) and fluorescence lifetime imaging (FLIM). These two methods allow to detect the presence of organic fluorescent materials and their distribution in the wall paintings [21]. * Mid-Fourier transform infrared spectroscopy (FTIR) fiber reflectance spectroscopy. The FTIR spectroscopy by portable instruments is commonly used to obtain information about the presence of both organic and inorganic material [22; 23; 24]. * Hyperspectral imaging in the NIR and mid-IR region. Present scientific attention is focused on the progress of mapping/imaging multi-/hyperspectral methods, since area examination naturally meets the demands of a holistic art approach by revealing not only the chemical composition of painting materials but also their semi quantitative spatial distribution with respect to what is visible to the naked eye. * These methods have been assessed and provided promising results in other types of paintings (with a clearly higher binder to pigment ratio) but possibly further developments will allow their successful application for the screening and mapping of also in wall paintings [25; 26; 27]. * Raman spectroscopy.