Lasers in the Conservation of Artworks VIII

Preservation of cultural legacy is essential for ensuring its availability for future generations. Long-term indoor storage can sometimes cause the papers to adhere, which can result in the transfer of ink stamps or prints from paper to paper, and subsequently, there emerges the need to remove these types of stains. Laser cleaning emerged as a promising technique for paper surface cleaning. This work presents the laser cleaning of a historical paper dated to the end of the 19th century using the Nd:YAG laser in a nanosecond pulsed regime, at two wavelengths, 532 and 1064 nm, and a semiconductor laser in a continuous regime, at a 552 nm wavelength. The cleaned areas are observed by optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy, and spectrophotometry. The obtained results are discussed in terms of the laser cleaning efficiency characterized by several aspects. The results obtained by green and near-IR laser irradiation in pulsed and continuous regime are compared, showing favorable effects regardless of the laser wavelength. However, in some cases, laser cleaning at 1064 nm wavelength damaged the surface layer of the paper. Cleaning at 532 nm wavelength did not completely remove the ink, and the ink traces were visible under the microscope or spectrometer. The proposed efficient cleaning method for stain, dust, and stamp ink removal from historical papers includes a semiconductor laser at 552 nm, owing to the continuous action of its beam.

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Investigating the Potential of the Er:YAG Laser for the Removal of Cemented Dust from Limestone and Painted Plaster

Melita

Węgłowska

Tamburini

et al. 2020

Coatings

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A successful application of Er:YAG laser for the cleaning of a restored Assyrian relief sculpture from the British Museum collection is presented. Displayed in the gallery, the sculpture has darkened over time due to the natural deposition of dirt, in particular on restored parts. Since traditional cleaning methods have demonstrated to be unsuccessful, a scientific investigation was performed to identify the composition of the soiling and the materials used for the restoration. The analysis suggested the presence of gypsum, calcium oxalate, carbonates and alumino-silicates on the encrustation. The molded plaster, composed of lime and gypsum and pigmented aggregates, was likely prepared at the end of the 19th century to mimic the stone color. It was repainted with what was identified as a modern oil-based overpaint, applied to cover darkening during a second conservation treatment in the 20th century. Laser trials were first performed on small areas of the objects and on mock-ups to determine the critical fluence thresholds of the surface, investigated through visual examination and analyses using Fourier transform infrared spectroscopy (FTIR) and Pyrolysis-gas chromatography-mass spectrometry (Py–GC–MS). The right parameters and conditions to be used during the cleaning process were, therefore, determined. The chemical selectivity of the cleaning process allowed us to complete the treatment safely while preserving the restoration.

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Lasers in the Conservation of Artworks VIII

Cited by 4 publications

References 63 publications

Laser cleaning in conservation of stone, metal, and painted artifacts: state of the art and new insights on the use of the Nd:YAG lasers

Laser cleaning in conservation of stone, metal, and painted artifacts: state of the art and new insights on the use of the Nd:YAG lasers

Application of semiconductor continuous and Nd:YAG pulsed laser processing for nondestructive cleaning of the historical paper

Investigating the Potential of the Er:YAG Laser for the Removal of Cemented Dust from Limestone and Painted Plaster

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