Initial results indicate that a comparative study of the results might provide a secure hypothesis for the complex matter of damage of oil media on paper recorded by the conservators. However, the need of a non-destructive methodology for the evaluation of the condition of the works and the determination of stage of deterioration is regarded significant as they are associated with the preservation decision making for a wide range of cultural heritage objects. The application of non-destructive imaging techniques, digital  
Figure 23: N. Gysis, Sewing studio (19 th c.), oil sketch, National Gallery. Discoloration due to oil medium absorption is evident on the verso side. microscopy, GC-MS analysis of VOC absorbed by a SPME needle, and FTIR analysis will be discussed. ## References  
* Banou and Alexopoulou (2015) Banou, P.; Alexopoulou, A.; Singer, B.W. The Treatment of Oil Paintings on Paper Supports Considerations on the Treatment Applications Used from the Past until the Present. _J. Pap. Conserv._**2015**, _16_, 29-36. * Kosek and Green (1992) Kosek, J.; Green, L.R. A Survey of Oil Paintings and Sketches on Paper in the Collection in the British Museum: An Assessment of Stability. _IPC Conf. Pap. Manch._**1992**, 96-102. * Daniels (1989) Daniels, V. Oxidative damage and the preservation of organic artifacts. _Free. Radic. Res. Commun._**1989**, \(5\), 213-220. * Banou et al. (2016) Banou, P.; Alexopoulou, A.; Chranioti, C.; Tsimogiannis, D.; Terlixi, A.V. ; Zervos, S.; Singer, B.W. The effect of oil binders on paper supports via VOC analysis. _J. Cult. Herit._**2016**, _20_, 589-598. * _Determining Optimum Irradiation Conditions for Analysis of Heritage Materials by Raman Spectroscopy_
* _Philippidis_1,* and D. Anglos_1,2
* Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas (IESL-FORTH), 70013 Heraklion, Greece
* Department of Chemistry, University of Crete, 70013 Heraklion, Greece
* Correspondence: filagg@iessl.forth.gr  
Continuous advances in photonic technologies have made available a broad range of spectroscopic methods based on intense radiation sources, which scientists have employed in various analytical investigations aiding archaeologists, historians, and conservators in their studies and practice [1]. While most of these techniques are considered non-destructive as no sampling is needed, it is conceivable that during analysis photons or particles could potentially induce alterations on the analyzed material depending both on the nature of the substrate and the irradiation parameters. The literature considering radiation effects on Cultural Heritage (CH) objects is rather limited to date [2,3]. In this study, Raman systems with different laser excitation sources, portable and laboratory, were employed for investigating samples of pigments both in pure form and in the presence of binding medium and varnish. The Raman spectrometers were used as irradiation and monitoring tool. The work concentrates on the effects of laser irradiation on inorganic pigments which are considered common reference materials for accessing pigments discoloration effects during laser irradiation. Vermillion (\(\alpha\)-HgS), Prussian blue (Fe\({}_{4}\)[Fe(CN)\({}_{6}\)]\({}_{3}\)), red lead (Pb\({}_{3}\)O\({}_{4}\)), massict (PbO), and cadmium pigments (CdS and CdS\({}_{x}\)Se\({}_{y}\)) are investigated in pure form (powder) and in different chemical environments. It is important to understand the physics and chemistry underlying light induced alterations for various paint materials. The study of different exposure parameters (laser power, exposure time, etc.) is crucial for the development of proper mitigation strategies and to establish safe irradiation boundaries and protocols for the use of Raman microscopy in art conservation. ## References  
* Anglos (2017) Anglos, D. Shedding light on the past: Optical technologies applied to cultural heritage. _Herit. Sci._**2017**, \(5\), 29. * Bertrand et al. (2015) Bertrand, L.; Schoeder, S.; Anglos, D.; Breese, M.B.H.