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Nd:YAG vs Er:YAG : a comparative study of laser varnish removal on easel paintings

JUN
24
2019
24. JUN 2019

Lecture Hall ICM - Internationales Congress Center München SPIE Optical Metrology > Optics for Arts, Architecture, and Archaeology VII > 3D Tomography: Applications

09:20-09:40 h | ICM - Internationales Congress Center München ICM Room 12a

Subjects: Optical Measurement Systems / Optical Metrology

Type: Lecture

Speech: English

Cleaning of easel paintings includes the removal of pollutants from the surface of varnishes or paint layers, the partial or complete removal of aged varnishes, and the removal of unwanted overpaintings. These operations aim at restoring the readability of the artwork. Conservators generally use chemical or mechanical actions to eliminate these materials. When confronted with poorly soluble varnishes or binders, conservators are forced to use aggressive chemical solutions. Their penetration degree is hard to assess and they can be harmful for the operator’s health. In the case of very fragile artworks, any mechanical action can induce irreversible damage to the original material. In these cases, control and innocuity of the cleaning operation can be challenging. Laser-matter interaction processes are an interesting alternative to traditional methods in such very demanding cases. It generally involves two distinct methodologies : the first one consists in directly ablating the layer with a pulsed ultraviolet laser [1] while the second implies laser softening of the material which can then be removed with a mild chemical product [2]. In this study, we propose a parametric comparison of these two laser-matter interaction processes for the removal of natural varnish (dammar) from well-known photosensitive tempera painting [3] (minium and lead white). For the ablation experiment, we used the fourth harmonic of a nanosecond Neodymium:YAG laser (Quantel CFR 10 ns 50 mJ 266 nm). For the hybrid approach, a commercial microsecond Erbium:YAG laser (El.En. “Light Brush 2” 2940 nm) was used, combined with a mild solvent. Layer thickness measurements prior and after cleaning was performed by Spectral Domain-Optical Coherence Tomography (Thorlabs GAN220-OCT Base Unit + Thorlabs OCTP900M Scanner) to compare cleaning resolutions with both techniques. Treatment innocuity was controlled by X-ray diffraction and pulsed Raman spectroscopy to detect any pigment modification. Finally, given that cleaning of easel paintings can be very time consuming, a comparison of the duration of the operation is proposed. [1] C. Fotakis, “Lasers for art’s sake,” Optics and Photonics News, vol. 6, no. 5, pp. 30–35, 1995. [2] A. De Cruz, M. L. Wolbarsht and S. A. Hauger, “Laser removal of contaminants from painted surfaces,” Journal of Cultural Heritage, vol. 1, no. 2, pp. S173–S180, 2000 [3] P. Pouli and D. C. Emmony, “The effect of Nd: YAG laser radiation on medieval pigments,” Journal of Cultural Heritage, vol. 1, no. 2, pp. S181–S188, 2000

Informations

Location

Eingang
Nord-West
ICM
Eingang
Nord
Eingang
West
Atrium
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Nord-Ost
Eingang
Ost
Conference
Center Nord
Freigelände
C1
C2
C3
C4
C5
C6
B0
B1
B2
B3
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B5
B6
A1
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A3
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A5
A6

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