Cleaning of daguerreotypes with an excimer laser

Turovets, Igor; Maggen, M.; Lewis, Alan

doi:10.1179/sic.1998.43.2.89

Cited by 10 publications

(10 citation statements)

References 11 publications

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“…In most of the cases, silver colours present dramatic blackening, but in some manuscripts, the metal brightness is still present. Although the application of silver leaf in illuminated manuscripts has been referred by several authors [13][14][15][16][17][18][19][20][21][22][23][24][25], the study of silver degradation in the cultural heritage field has been mainly associated with metal artefacts, jewellery or composite objects such as altarpieces, polychrome and gilded objects, silver threads in textile, daguerreotype photos and silverpoint drawings [26][27][28][29][30][31][32][33][34][35][36][37][38]. Despite its importance for cultural heritage preservation, there is little consensus on the literature regarding silver degradation mechanisms.…”

Section: Introductionmentioning

confidence: 99%

Silver paints in medieval manuscripts: a first molecular survey into their degradation

et al. 2018

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The lack of comprehensive studies on silver paints in manuscripts is a handicap to new stabilization strategies and treatments. This work develops and tests a methodological approach for the study of the degradation of silver paints, at the molecular level, using as a case study a French Book of Hours dated from the 15th century from Mafra National Palace collection. In this paper, we show that the global equation commonly used by the cultural heritage community to describe the tarnishing of silver proves to be insufficient to understand the main factor causing its severe and extensive darkening in medieval illuminated manuscripts. This equation depicts the degradation of silver instantly with a sulphide containing species as H 2 S. Recent research has solidly proved that the first intermediate of silver oxidation is Ag 2 O. This theme will be presented in a forthcoming review. Within this framework, we selected four typologies of silver paints, all analysed by in situ techniques and four as microsamples; due to the very small size and fragility of the microsamples, new methods of sample preparation were developed and tested. The main research questions include: (1) understanding how silver-based colour are formed, disclosing its full stratigraphy; (2) define if the other compounds present, such as colour paints and the ground, may affect silver oxidation by stabilizing or accelerating it; (3) comprehend if it is possible to characterize the degradation products of silver paints with the methodology developed in this work, both in the bulk and at the interfaces between layers. Overall our results show that silver-based colours exhibit a complex stratigraphy that impacts its conservation condition. Further research at the molecular level is required on the correlation of the main components of the ground (binder and filler such as gypsum and calcium carbonate) and the paints that are applied as layers over or under the silver leaf. Our case studies have shown that both in situ analytical techniques and scanning electron microscopy with energy dispersive spectroscopy analysis in the microsamples, provide relevant information on the silver colour stratigraphy. However, the information obtained studying cross-sections is more accurate. We consider that the study of the degradation mechanism of silver in medieval illuminated manuscripts will require the combination of both approaches; in situ methodologies support the relevance of the data acquired on the microsamples. Microsamples studies will make possible the acquisition of data that is fundamental to understand the darkening of silver paints and this, in turn, is essential to develop informed and sustainable conservation policies.

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Section: Introductionmentioning

confidence: 99%

Silver paints in medieval manuscripts: a first molecular survey into their degradation

et al. 2018

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“…The evaporation threshold of the silver sulfide and the melting threshold of the silver plays a crucial role in the ablation rate[14]. As clear from previous literature[7], the sulphur gets dissociatedfrom silver at around 838 K while the melting point of silver is around 1234 K. A good ablation rate can be achieved if applied fluence can generate temperature within this range. The trend of decrease of sulphur is present in all the cases.…”

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confidence: 88%

Excimer laser cleaning of black sulphur encrustation from silver surface

Raza

Das

Tudu

et al. 2019

Optics & Laser Technology

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The process of localized cleaning of silver sulphide from the silver surface has been investigated in this work. An artificial black encrustation was generated on the silver surface and its laser cleaning was performed using an excimer laser (KrF based) working at a wavelength of 248 nm and pulse width 25 ns. Laser process parameters i.e. laser fluence and number of pulses were used to perform the experiment and after different optical, microstructural, elemental, microhardness and surface topography analysis of the laser ablated zone was performed. The parametric window selected for the excimer laser cleaning were laser fluence (200-400 mJ/cm 2 ), repetition rate 4 Hz and number of pulses (60-300). It was observed that excimer laser is very effective in the cleaning of black encrustation having ~ 6 wt. % of sulphur from the surface without any significant removal of the silver substrate. The fluence value of 260.48 mJ/cm 2 was observed as above threshold value for removal of sulphide from the encrusted surface while a fluence of 384.85 mJ/cm 2 and 220 pulses showed the maximum removal of sulphur encrustation (~0.38 wt. % of sulphur remaining). Formation of the peripheral rim was observed to occur above 280.17 mJ/cm 2 of fluence value. The topography of the ablated surface showed a removal of 5-10 µm of the sulphide layer from the surface whereas the thickness of the sulphide coating was around 8-10 µm. Microhardness value showed a change of microhardness of the silver surface from 75.12 HV 0.5 (uncoated parent silver) to 96.07 HV 0.5 (centre of the ablated zone).Finally, it was concluded that excimer laser cleaning is a novel method for localized removal of silver sulphide encrustation from silver surface.

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“…However, this process is ineffective in cleaning ungilded and colored plates. Cleaning daguerreotypes using an excimer laser (2.5 ns) was explored by Turovets et al They observed removal of the tarnish without degradation to the image at 73 fluencies of 0.1-0.12 J/cm [1]. The process was successful on both colored and ungilded plates.…”

Section: Introductionmentioning

confidence: 97%

“…The removal of this tarnish from daguerreotypes has been attempted many times before [1][2][3][4]. Chemical cleaning causes fading of the image due to damage to both the substrate and image particles.…”

Section: Introductionmentioning

confidence: 98%

“…Chemical cleaning causes fading of the image due to damage to both the substrate and image particles. Low temperature plasma cleaning leaves faint white areas behind after cleaning and does irreversible damage to the silver substrate [1]. The most common means to restore daguerreotypes at present is electrocleaning, which refers to immersing the plate in an alkali solution with a silver electrode and running current through the system [4].…”

Section: Introductionmentioning

confidence: 99%

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Ultrafast Laser Cleaning of Daguerreotypes

et al. 2011

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An ultrafast laser irradiation method for the removal of corrosion from Daguerreotypes without detrimentally affecting image quality has been developed. Corrosion products such as silver oxide and silver sulfide may be removed by chemical cleaning but these reactions are hard to control and are often damaging to the underlying silver, ruining the image. The Ti:Sapphire 150 fs laser pulses used in this study are focused to a beam diameter of 60 m and are normally incident to the Daguerreotype. It was found that the corrosion layer has a lower material removal threshold than silver allowing for removal of corrosion with minimal removal of vital information contained in the silver substrate.

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Cleaning of daguerreotypes with an excimer laser

Cited by 10 publications

References 11 publications

Silver paints in medieval manuscripts: a first molecular survey into their degradation

Silver paints in medieval manuscripts: a first molecular survey into their degradation

Excimer laser cleaning of black sulphur encrustation from silver surface

Ultrafast Laser Cleaning of Daguerreotypes

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