Cultural heritage objects are continuously threatened by surface contamination, degradation, and the formation of defects such as cracks and craquelure. Conservators therefore require highly precise, minimally invasive methods that can selectively remove unwanted deposits or repair damaged surfaces without compromising the original material. Laser ablation offers such a solution through the controlled interaction between laser radiation and matter, enabling intentional and highly localized modifications of the material. In this context, lasers have become sophisticated conservation tools for both cleaning and mending. For cleaning applications, lasers function as "light scalpels," selectively removing unwanted surface layers while preserving the underlying sensitive historic substrate. For mending applications, they can act as minute "light blowtorches," locally melting a controlled volume of glaze to bridge and fill gaps created by craquelure. For more than 30 years, IESL-FORTH has been conducting pioneering research to optimize laser processing parameters according to the physicochemical properties of each material. This work has enabled the development of highly precise, effective, and safe laser-based methodologies tailored to the conservation of cultural heritage. A number of laser systems with different wavelength, pulse duration and energy output characteristics are available for laser conservation investigations such as: A) Q-switched Nd:YAG lasers emitting both nano- and pico-second laser pulses at various wavelengths (such as 1064, 532, 355, 266 and 213nm) B) various excimer lasers emitting nano, pico and femto-second pulses in the UV (248, 193nm), C) a patented ns Nd:YAG system with dual wavelength beam output (1064 and 355nm), developed for the laser cleaning project of the Athens Acropolis Monuments specially dedicated to remove pollution crust from stonework without any discoloration or damage, D) a LQS Nd:YAG system emitting IR pulses at longer pulse-widths, E) an Er:YAG laser system emitting at 2940 nm and F) a continuous CO2 laser system for the patented application related to the laser conservation of glazed objects. Various workstations adjustable for different laser cleaning applications with the ability to integrate different optical and opto-mechanical components for the most appropriate beam delivery and control are available; A) either through handheld units (using an articulated arm) or B) through automated beam scanning units for micrometer control and guidance of the laser beam to the sample (i.e. the painting surface). The latter, a computer-driven mechanised component, can be adjusted based on fluence values, spot size and pulse repetition rate enabling thus the homogeneous scanning of predefined areas. Furthermore, a number of multi-modal diagnostic instruments for in-situ assessment of the cleaning result and monitoring of the laser ablation procedure are also available. These can be selected according to the specifications of each individual cleaning case and may be one or more of the following: Spectral Imaging to visualise the cleaning state, Laser Induced Fluorescence (LIF) to evaluate the thinning of varnish, Vis – NIR Diffuse Reflectance spectroscopy to chemically characterise the irradiated surfaces and so on. Potential Results Cleaning methodologies for a wide range of conservation challenges including: - various crusts or aged polymeric/organic coatings/varnishes from paintings/wall-paintings/painted surfaces; - inorganic crusts from various substrates (stone, metals, bone, wood etc. to name a few); Preliminary and feasibility studies to determine the optimum parameters can be performed either on technical mock-ups, as well as on samples taken from the actual objects.

Other

Laser ablation/ Laser cleaning/ laser mending

research on conservation (cleaning or mending) methdologies

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