The two-wavelength laser cleaning methodology has been introduced and developed in order to meet demanding cleaning challenges in CH. The innovation lies on the combined use of two laser beams, allowing thus control of the laser ablation effective regimes towards an efficient and safe cleaning result. A series of studies on technical samples and real fragments aimed at defining and refining this methodology in order to ensure that the original surface, including its details and historic traces, will be safeguarded. In this paper related research and applications will be presented in an attempt to enlighten the associated laser ablation processes, as well as the potential cleaning applications in CH field. Laser-assisted removal of pollution accumulations from the Athens Acropolis monuments and sculptures is a unique highlight on the use of this methodology in practice. IESL-FORTH in collaboration with the Acropolis Restoration Service and the Acropolis Museum has developed an innovative cleaning methodology and a prototype laser cleaning system, which since 2002 have been introduced to the everyday conservation practice and will be presented in this paper.

This work presents a corpus of measurement methodologies utilized during a multidisciplinary project, aiming at the protection and conservation of ancient steel joints (clamps and dowels) of the Acropolis monuments, undertaken by the Acropolis Restoration Service (YSMA). The Laboratory of Physical Chemistry of the National Technical University of Athens collaborated with YSMA in designing and evaluating laboratory scale and field experiments, aiming in testing conservation materials. The first phase involved the application of seven coating systems on uncorroded metal coupons. The application characteristics, physicochemical properties (colour, gloss, hydrophobicity), and the protection performance against accelerated corrosion and polymer photo-oxidation were measured. Poligen CE12 and Paraloid B67 +2% nano-alumina were selected as the two most suitable materials for pilot applications on corroded steel joints and outdoor field exposure at the monument site. The assessment of the two coatings reversibility and of the corroded surfaces chemical alteration was undertaken by Raman spectroscopy analyses and orthophotographic documentation. During the 1-year field exposure, the corrosion development was retarded, but some local events of active corrosion could not be prevented. The joint areas coated with Paraloid B67 enhanced with 2% nano-alumina enabled more uniform application on corroded surfaces and exhibited better corrosion protection. In case of Poligen CE12, the nature of corrosion products indicated local acceleration of corrosion reactions.