Laser cleaning of paintings: in situ optimization of operative parameters through non-invasive assessment by optical coherence tomography (OCT), reflection FT-IR spectroscopy and laser induced fluorescence spectroscopy (LIF)

Patrizia Moretti; Magdalena Iwanicka; Kristalia Melessanaki; Evdoxia Dimitroulaki; Olga Kokkinaki; Melissa Daugherty; Marcin Sylwestrzak; Paraskevi Pouli; Piotr Targowski; Klaas Jan van den Berg; Laura Cartechini; Costanza Miliani

doi:10.1186/s40494-019-0284-8

Heritage Science

Table 1 Summary of FT-IR, OCT and LIF data obtained after the laser cleaning tests (series C—Fig. 1a, e) performed on the Floral painting

From: Laser cleaning of paintings: in situ optimization of operative parameters through non-invasive assessment by optical coherence tomography (OCT), reflection FT-IR spectroscopy and laser induced fluorescence spectroscopy (LIF)

Area	F = fluence (J/cm²)	N = number of pulses	Layer examined with FT-IR after cleaning		Average thickness of removed material (μm)	Layer examined with LIF after cleaning
C1a	1.1	30	Probably paint layer (noisy spectrum)	Wax and uppermost varnish removed, second upper varnish mostly removed, overpaint mostly removed; increased surface roughness	65 ± 21	The band at 473 ± 5 nm is reduced in intensity and red shifted to 483 ± 5 nm after cleaning A new band appears at 610 ± 5 nm
C1b	1.1	20	Probably paint layer (noisy spectrum)	Wax and uppermost varnish removed, second upper varnish mostly removed, overpaint mostly removed; increased surface roughness	69 ± 18
C2a	0.9	50	Probably paint layer (noisy spectrum)	Wax and two upper varnishes removed, overpaint mostly left; increased surface roughness	55 ± 14
C2b	0.9	40	Probably paint layer (noisy spectrum)		55 ± 14
C3a	0.9	20	Probably paint layer	Wax and two upper varnishes almost removed, overpaint not removed; increased surface roughness	42 ± 12
C3b	0.9	10	Natural varnish	Wax and uppermost varnish removed, second upper varnish reduced, overpaint intact	30 ± 6	Emission intensity is increased after laser irradiation. No other changes are observed
C4	0.7	25	Natural varnish	Wax and uppermost varnish partially removed, second upper varnish and overpaint not removed	19 ± 5
C5	0.7	46	Probably paint layer (noisy spectrum)	Wax and uppermost varnish removed, second upper varnish locally left, overpaint not removed; increased surface roughness	34 ± 10	The main band at 473 ± 5 nm is reduced in intensity and red shifted to 483 ± 5 nm after cleaning A new band appears at 610 ± 5 nm

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