IPERION CHIntegrated Platform for the European Research Infrastructure ON Cultural Heritage

MOLAB

MOLAB (Mobile LABoratory) is a network of facilities from Italy, France, Poland, Greece and Germany, providing a coherent access, under a unified management structure, to a set of portable equipment and related competences, for in-situ non-destructive measurements on artworks. Measurements are carried out in the same site where the actual artwork under examination is located or exhibited, i.e.  museum, restoration workshop, open air location etc.

Motivation for MOLAB arises from the fact that a large number of historical European patrimony consists of monuments, sculptures, buildings and that cannot be moved from their location and this implies that non-invasive material studies on these objects must be necessarily carried out in-situ, through portable instrumentation. In addition, even in the case of movable patrimony (such as paintings, ceramics, gems, manuscripts, etc.) it can be often quite difficult, if not impossible, to move such works to a laboratory, due the high risks and costs connected with their transportation and often fragile state.

Typical MOLAB users are Heritage researchers (either individuals or teams from public and/or private institutions) who are developing studies to:

  • clarify arthistorical or archaeological questions (execution techniques, dating, underdrawings in paintings, etc.
  • assess the state of conservation of artefacts
  • determine or test the optimal preservation strategy to slow down alteration processes; (d) monitor conservation treatments
  • inform risk assessment

 

What can MOLAB offer your project?

  • Your project may be orientated towards art‐historical or archaeological questions (execution techniques, dating, under‐drawings in paintings etc; assessing the state of conservation of artefacts; determine or test the optimal preservation strategy to slow down alteration processes; monitoring conservation treatments and informing risk assessment
  • MOLAB provides: analytical investigations carried out in situ on fragile artworks or precious archaeological pieces so that you don’t have to move them to a  laboratory. This access also allows immovable objects like sculptures, monuments and historical buildings to be studied
  • All the techniques are non invasive, so there is strictly no sampling or contact with the surface under exam
  • All our teams are made up of highly qualified and trained scientific staff that will accompany the portable instruments, help the Users and give tutorials on the use of the instrumentation
  • All the data collected during the MOLAB access automatically belongs to you for publishing and disseminating

 

MOLAB partners

MOLAB Italy: XRF, Raman, Micro-Raman, Vis-NIR reflectance, UV-VIS fluorescence, UV-Vis fluorescence time-decay, Fiber optic near-FTIR, Total reflection mid-FTIR, Macro XRF scanning, Micro XRF scanning, Scanning multispectral Vis-NIR reflectography, Vis hyperspectral imaging, Atomic force microscopy, Confocal microscopy

MOLAB France: Integrated XRF/XRD, SIRT, Thermography, NIR hyperspectral imaging, Terahertz imaging

MOLAB Poland: Optical Coherence Tomography

MOLAB Greece: Digital Holographic Speckle Pattern Interferometry

MOLAB Germany: NMR relaxometry, NMR depth-profiling

 

The MOLAB TNA Helpdesk can provide your draft proposals with any technical and scientific support, anytime, so that tailored proposals can be submitted before the deadlines.

 

Contacts
Name: Costanza Miliani
Phone: +39 075 5855639
Email: costanza.miliani@cnr.it

 

Specifications of the available techniques

XRF (X Ray Fluorescence)
Type: Spectroscopic point analysis

 

Overview

The new Portable X-ray fluorescence offered by MOLAB is designed for in-situ analyses being extremely portable, fast and completely non-destructive. It allows for a determination of the elemental composition (Z>12) of materials and is of great interest for heritage science applications particularly in the examination of all types of paintings, manuscripts, monuments and metals etc.

It is highly effective for a first hypothesis towards artist pigments identifications, specifically inorganic constituents, highlighting pentimenti, retouchings and over-paintings etc.

Technical details

The Elio portable XRF Analyzer (PXRF) is composed of a large area Silicon Drift Detector: 25mm2 XRF Detector, 130 eV at MnKα with 10 kcps input photon rate (high resolution mode), 170 eV at MnKα with 200 kcps input photon rate (fast mode). It has a fast (USB 2.0) 8k channels MCA with high resolution and high count-rate capability. Its excitation source is a transmission X-Ray generator, 5-200 μA, 10-40 kV, Rh anode with 1mm collimator filter sets. It has two pointing lasers (axial and focal), a microscope camera permitting on field adjustments on analysis. A mounting tripod (height 43-188cm) completes the set-up.

Further readings
  1. C. Miliani, F. Rosi, B. G. Brunetti, A. Sgamellotti, In situ Non-invasive Study of Artworks: The MOLAB Multitechnique Approach, Acc. Chem. Res., 2010, 43 (6), 728-738
  2. V. Capogrosso, F. Gabrieli, S. Bellei, L. Cartechini, A. Cesaratto, N. Trcera, F. Rosi, G. Valentini, D. Comelli and A. Nevin, An integrated approach based on micro-mapping analytical techniques for the detection of impurities in historical Zn-based white pigments, J. Anal. At, Spectrom., 2015, 30, 828-838
Providers

MOLAB Italy:  CNR-ISTM

Raman (λexc. 785 & amp; 1064 nm)
Type: Spectroscopic point analysis

 

Overview

Raman spectroscopy is a molecular vibrational spectroscopic technique which provides complementary information to FTIR. It is used in the cultural heritage field for the vast  identification and characterization of inorganic and/or limited organic materials. The main drawback of this technique is related to high fluorescence emissions which may compete with the scattering phenomena and cover any useful vibrational signals. However, to overcome this limitation we provide portable Raman instrumentations with multiple laser excitations at 532nm, 785nm and 1064nm which are interchangeable according to the object under study. Namely the 532nm laser system in a micro-Raman set-up is particularly adapt to low fluorescing inorganic based substrates, such as ceramics, bronzes and stone materials. The longer wavelength lines at 785nm and dispersive 1064nm favour the examination of organics (synthetic dyes and pigments, numerous natural dyes and pigments) and organic containing matrices, such as paintings (varnished and not) and manuscripts.

Technical details

The Jasco portable micro-Raman is equipped with a Nd:YAG laser source emitting at 532 nm. The system is equipped with a CCD ANDOR detector maintained at −50° C with a Peltier cooler. The use of optical fibres, Olympus objectives (50x or 20x), suitable notch filters and a CCD camera which permit the image of the irradiated sample to be visualised. The spatial resolution of this system is 100 μm (20x objective) with a spectral resolution of about 10 cm-1.

The portable Raman spectrometer Rigaku Xantus-2, has lasers operating at 785 and 1064 nm. For the 785 nm laser set-up, the detector is a CCD cooled by a Peltier system and the power ranges from 30- 490 mW with a spectral resolution between 7 -10 cm-1. The 1064 nm laser set-up instead uses an InGaAs detector and has power varying from 30- 490 mW with a spectral resolution of 15 -18 cm-1. The spatial resolution is about 4 mm2.

Further readings

  1. C. Miliani, F. Rosi, B.G Brunetti, A. Sgamellotti, “In situ Non-invasive Study of Artworks: the MOLAB Multi-technique Approach”, Accounts of Chemical Research 43, 2010, pp. 728-738.
  2. F. Rosi, V. Manuali, T. Grygar, P. Bezdicka, B.G. Brunetti, A. Sgamellotti, L. Burgio, C. Seccaroni, C. Miliani, “Raman scattering features of lead pyroantimonate compounds: implication for the non-invasive identification of yellow pigments on ancient ceramics. Part II. In-situ characterization of Renaissance plates by portable micro-Raman and XRF”, Journal of Raman Spectroscopy, 42, 2011, pp. 407–414.
Providers

MOLAB Italy:  CNR-ISTM

 

Micro-Raman (λexc. 532 nm)
Type: Spectroscopic point analysis

 

Instrument name
Portable MicroRaman: Jasco
Portable Raman: Rigaku Xantus-2
Overview

Raman spectroscopy is a molecular vibrational spectroscopic technique which provides complementary information to FTIR. It is used in the cultural heritage field for the vast  identification and characterization of inorganic and/or limited organic materials. The main drawback of this technique is related to high fluorescence emissions which may compete with the scattering phenomena and cover any useful vibrational signals. However, to overcome this limitation we provide portable Raman instrumentations with multiple laser excitations at 532nm, 785nm and 1064nm which are interchangeable according to the object under study. Namely the 532nm laser system in a micro-Raman set-up is particularly adapt to low fluorescing inorganic based substrates, such as ceramics, bronzes and stone materials. The longer wavelength lines at 785nm and dispersive 1064nm favour the examination of organics (synthetic dyes and pigments, numerous natural dyes and pigments) and organic containing matrices, such as paintings (varnished and not) and manuscripts.

Technical details

The Jasco portable micro-Raman is equipped with a Nd:YAG laser source emitting at 532 nm. The system is equipped with a CCD ANDOR detector maintained at −50° C with a Peltier cooler. The use of optical fibres, Olympus objectives (50x or 20x), suitable notch filters and a CCD camera which permit the image of the irradiated sample to be visualised. The spatial resolution of this system is 100 μm (20x objective) with a spectral resolution of about 10 cm-1.

The portable Raman spectrometer Rigaku Xantus-2, has lasers operating at 785 and 1064 nm. For the 785 nm laser set-up, the detector is a CCD cooled by a Peltier system and the power ranges from 30- 490 mW with a spectral resolution between 7 -10 cm-1. The 1064 nm laser set-up instead uses an InGaAs detector and has power varying from 30- 490 mW with a spectral resolution of 15 -18 cm-1. The spatial resolution is about 4 mm2.

Further readings
  1. C. Miliani, F. Rosi, B.G Brunetti, A. Sgamellotti, “In situ Non-invasive Study of Artworks: the MOLAB Multi-technique Approach”, Accounts of Chemical Research 43, 2010, pp. 728-738.
  2. F. Rosi, V. Manuali, T. Grygar, P. Bezdicka, B.G. Brunetti, A. Sgamellotti, L. Burgio, C. Seccaroni, C. Miliani, “Raman scattering features of lead pyroantimonate compounds: implication for the non-invasive identification of yellow pigments on ancient ceramics. Part II. In-situ characterization of Renaissance plates by portable micro-Raman and XRF”, Journal of Raman Spectroscopy, 42, 2011, pp. 407–414.
Providers

MOLAB Italy:  UNIPG S.M.A.Art

 

Vis-NIR Reflectance
Type: Spectroscopic point analysis

 

Overview

In situ reflectance and fluorescence UV-VIS-NIR spectroscopy in the last several years has become acknowledged as an effective non invasive technique for the identification of several organic and inorganic materials used in artworks production (such as paintings, manuscripts, textiles etc). To this end, fluorescence measurements are particularly indicated for the characterization of ancient colorants as well as luminescent pigments such as zinc oxide, cadmium based pigments and also Egyptian blue. Moreover, fluorophores with similar emission spectra can be distinguished by measuring fluorescence decay lifetimes.

Technical details 

The portable instrumental prototype is composed of a compact Deuterium-Halogen lamp suitable for reflectance measurements; lasers and diode laser sources for steady-state fluorescence measurements; pulsed diode lasers and LEDs for time-resolved fluorescence experiments in the ns-ms lifetime range.

They are coupled with high sensitive CCD spectrometers working in the UV-VIS-NIR which allow reflectance spectra between 200-1600 nm and fluorescence spectra in the 300-1600 nm range to be collected. Lifetimes can be measured for species emitting in the 350-850 nm spectral range.

A dedicated fibre optic system allow measurements on any surface to be done. The size of the whole probe is less than 2 mm2.

Providers

MOLAB Italy: UNIPG S.M.A.Art

UV-Vis Fluorescence
Type: Spectroscopic point analysis

 

Overview

In situ reflectance and fluorescence UV-VIS-NIR spectroscopy in the last several years has become acknowledged as an effective non invasive technique for the identification of several organic and inorganic materials used in artworks production (such as paintings, manuscripts, textiles etc). To this end, fluorescence measurements are particularly indicated for the characterization of ancient colorants as well as luminescent pigments such as zinc oxide, cadmium based pigments and also Egyptian blue. Moreover, fluorophores with similar emission spectra can be distinguished by measuring fluorescence decay lifetimes.

Technical details 

The portable instrumental prototype is composed of a compact Deuterium-Halogen lamp suitable for reflectance measurements; lasers and diode laser sources for steady-state fluorescence measurements; pulsed diode lasers and LEDs for time-resolved fluorescence experiments in the ns-ms lifetime range.

They are coupled with high sensitive CCD spectrometers working in the UV-VIS-NIR which allow reflectance spectra between 200-1600 nm and fluorescence spectra in the 300-1600 nm range to be collected. Lifetimes can be measured for species emitting in the 350-850 nm spectral range.

A dedicated fibre optic system allow measurements on any surface to be done. The size of the whole probe is less than 2 mm2.

Providers

MOLAB Italy: UNIPG S.M.A.Art

UV-Vis Fluorescence time-decay
Type: Spectroscopic point analysis

 

Overview

In situ reflectance and fluorescence UV-VIS-NIR spectroscopy in the last several years has become acknowledged as an effective non invasive technique for the identification of severa organic and inorganic materials used in artworks production (such as paintings, manuscripts, textiles etc). To this end, fluorescence measurements are particularly indicated for the characterization of ancient colorants as well as luminescent pigments such as zinc oxide, cadmium based pigments and also Egyptian blue. Moreover, fluorophores with similar emission spectra can be distinguished by measuring fluorescence decay lifetimes.

Technical details 

The portable instrumental prototype is composed of a compact Deuterium-Halogen lamp suitable for reflectance measurements; lasers and diode laser sources for steady-state fluorescence measurements; pulsed diode lasers and LEDs for time-resolved fluorescence experiments in the ns-ms lifetime range.

They are coupled with high sensitive CCD spectrometers working in the UV-VIS-NIR which allow reflectance spectra between 200-1600 nm and fluorescence spectra in the 300-1600 nm range to be collected. Lifetimes can be measured for species emitting in the 350-850 nm spectral range.

A dedicated fibre optic system allow measurements on any surface to be done. The size of the whole probe is less than 2 mm2.

Providers

MOLAB Italy: UNIPG S.M.A.Art

Fiber optic near-FTIR
Type: Spectroscopic point analysis

 

Overview

NIR spectroscopy has become an increasingly useful analytical tool for non-invasive, contactless measurements by providing signals that are characteristic of infrared combination and overtone bands which have very low absorption coefficients. This technique is suitable for analysing organic and limited inorganic materials, by providing distinctive features regarding both chemical composition and physical properties (crystallinity, crystal shape and particle size). As the NIR radiation is particularly penetrating, it can typically pass through paint layers and reach the ground layer of paintings providing information of pigments and binders alike. Main drawbacks include however difficult band assignments which can be alleviated by the application of successive derivative transformations and multivariate data processing procedures.

Technical details

The JASCO NIR spectrometer provides information across the spectral region of the near infrared (12500 – 4000 cm-1 ). It consists of a halogen lamp as source,  an InGaAs detector and a 2m fiber optic sampling probe. The Y shaped silica-glass fiber optic probe contains of 14 fibers, 7 of which carry infrared radiation from the source to the sample, while the other 7 collect the radiation reflected off the surface.  Spectral resolution is 4 cm-1  with a sampling area of about 12  mm2 and an artwork-probe working distance of about 6mm.

Further readings

1. F. Rosi, C. Miliani, et al. An integrated spectroscopic approach for the non invasive study of modern art materials and techniques” Applied Physics A, 100; 2010 pp. 613.
2. M. Vagnini, C. Miliani  et al. FT-NIR spectroscopy for non-invasive identification of natural polymers and resins in easel paintings. Anal Bioanal Chem. 395; 2009 pp. 2107-18.

Providers

MOLAB Italy: UNIPG S.M.A.Art

Mid-FTIR
Type: Spectroscopic point analysis

 

Overview

Reflection mid-FTIR spectroscopy is widely used in the field of cultural heritage for the characterization and identification of organic and inorganic materials. Being a vibrational molecular spectroscopic technique, it provides information concerning the functional groups constituting the molecules ultimately aiding a molecular identification of unlimited materials under exam (from any painted surface (ancient, modern, contemporary), manuscripts, monuments etc). It is particularly adapt for the recognition of inorganic pigments (with some limitations from metal oxides) as well as limited synthetic and natural organic pigments classes. This technique can also be used to characterize the organic materials present in associated binding media or varnishes as well as provide information concerning any surface contaminations, alterations and products/processes of degrade.

Technical details

The portable ALPHA spectrometer collects infrared radiation reflected from a surface located at 1cm distance. This instrument consists of an infrared source and a Globar DLaTGS detector. It exploits a range from 7500 cm-1 -400 cm-1 and a spectral resolution of 4 cm-1 with a spatial resolution of about 28 mm2.

The portable JASCO VIR 9500 spectrophotometer is equipped with a mid-infrared fiber optic sampling probe. It observes a good signal-to-noise ratio is very good in the range 900 to 4000 cm-1 with the exception of the 2050-2200 cm-1 region, with a spectral resolution is of 4 cm-1. The non-contact probe (4 mm diameter) is maintained perpendicular to the painting surface (0°/0° geometry) at a distance of about 6 mm. Owing to the probe geometry, reflectance mid-FTIR spectra can present large distortions, both in band shape and absorption frequency, due to the presence of both specular and diffused components. Interpretation of spectra is possible through a wide specific database created ad hoc.

Further readings
  1. C. Miliani, F. Rosi et al. Reflection infrared spectroscopy for the non-invasive in situ study of artists’ pigments. Applied Physics A-Materials Science & Processing 106; 2012 pp. 295-307
  2. D. Buti, F. Rosi et al., In-situ identification of copper-based green pigments on paintings and manuscripts by reflection FTIR. Analytical and Bioanalyti cal Chemistry 405, 2013 pp.2699-2711
  3. Monico L., Rosi F, Miliani C. et al. Spectrochimica Acta Part A-Molecular And Biomolecular Spectroscopy 116, 2013 pp. 270-28
Providers

MOLAB Italy: UNIPG S.M.A.Art (ALPHA); CNR-ISTM (JASCO)

 

 

Integrated XRD-XRF
Type: Spectroscopic point analysis

 

Overview

This is a transportable XRD-XRF device that can be operated for field work. It is an integrated system which permits simultaneous X-ray fluorescence and X-ray diffraction analyses to be carried out in the same position. The acquisition of the XRD patterns is done in reflection mode to avoid any contact with the works of art. The prototype instrument allows the characterization of the main materials characteristics: determination of the different phases (chemical composition, crystal structure) and the description of the microstructure (grain size, texture, lattice imperfections, etc.). Validation measurements have been carried out on different types of objects, such as paintings, ceramics and metals. The XRD diagrams obtained with the portable XRF/XRD instrument are comparable in quality with diagrams obtained with conventional laboratory equipment.

Technical details

The X-rays source is a copper anode tube, with a maximum 40Wpower:40 kV,1 mA. A collimating polycapillary system  gives a quasi parallel outgoing beam with a very low divergence. The diameter of the beam is about 4 mm. The XRF signal is collected with a SDD X fluorescence detector with a resolution less than 140 eV at 5.9 keV. The recording of the XRD patterns is performed with asilicon pixel detector (XPAD S70)of a 75 x 15 mm area with 67200 pixels; with a quantum efficiency of 99 % for 9 keV and 70 % for 15 keV. The system satisfies the requirements of the NF standard on the use of X rays.

Data treatment is aided by a database used in cultural heritage (mineral and organic phases), and permits at least a semi quantitative identification of the crystalline phase.

Further readings
  1. A. Gianoncelli, J. Castaing, L. Ortega, E. Doorhycée, J. Salomon, P. Walter, J.-L. Hodeau, P. Bordet, “A portable instrument for in situ determination of the chemical and phase compositions of cultural heritage objects”, X ray spectrometry, vol.37, (2008) 418-423M.
  2. Eveno, A. Duran, et J. Castaing, “A portable X-ray diffraction apparatus for in situ analyses of masters’ paintings “, Applied Physics A, vol. 100, no 3,(2010), 577‑584.
  3. L. Beck, H. Rousselière, J. Castaing, A. Duran, M. Lebon, B. Moignard, et F. Plassard, “First use of portable system coupling X-ray diffraction and X-ray fluorescence for in-situ analysis of prehistoric rock art “, Talanta, vol. 129, (2014), 459‑464
Providers

MOLAB France: CNRS-C2RMF

Macro XRF Scanning
Type: Multi/HyperSpectral Imaging

 

Overview

MOLAB offers access to two scanning X-ray fluorescence (XRF) systems for micro and macro multi-element mapping of surfaces in a non-invasive manner. Elemental distribution maps at different spatial scales are of great interest for heritage science applications and particularly in the examination of paints and inks in ancient paintings and historical documents.

X-rays are highly penetrating and generally allow to non-destructively probe the entire painting stratigraphy. Hence the registration of elemental maps in a wide atomic number range (Z>12) allows for the investigation of the pigment use by the artist and for studying the historical evolution of the paint, also revealing hidden paint layersin the case of pentimenti, retouchings and over-paintings etc.

Here follows a brief description of the scanning XRF instrumentation available in the MOLAB platform.

 

Technical details

Macro-XRF scanning

The macro-XRF scanning systemfrom XGLab is equipped with a compact measuring head composed by a high efficiency X-ray generator source with an Rh anode (50kV and 200µA) and by a large area Silicon Drift Detector (SDD) (50 mm2, energy resolution of 130eV at MnKα) which allows for fast and sensitive multi-elemental analysis. An integrated video microscope camera is used to control and select thearea under investigationwhile two point lasers allows for exact point positioning at a measuring distance of 10 mm.The measuring head is mounted on a motorised frame with an X-Y-Z stage with continuous movement for mapping application.To this purpose the X-ray beam can be collimated on the sample surface with spot diameter of 0,5 or 2 mm to collect maps with dimensions of 5×5cm2 with 0,5mm of resolution or 45×60cm2 with 5mm of resolution, respectively. A fast digital electronics has been specifically developed for mapping application acquiring spectra for each pixel. A dedicated software is used for multi-element map reconstruction.

Providers

MOLAB Italy: CNR-ISTM

Micro XRF Scanning
Type: Multi/HyperSpectral Imaging

 

Overview

MOLAB offers access to two scanning X-ray fluorescence (XRF) systems for micro and macro multi-element mapping of surfaces in a non-invasive manner. Elemental distribution maps at different spatial scales are of great interest for heritage science applications and particularly in the examination of paints and inks in ancient paintings and historical documents.

X-rays are highly penetrating and generally allow to non-destructively probe the entire painting stratigraphy. Hence the registration of elemental maps in a wide atomic number range (Z>12) allows for the investigation of the pigment use by the artist and for studying the historical evolution of the paint, also revealing hidden paint layersin the case of pentimenti, retouchings and over-paintings etc.

Here follows a brief description of the scanning XRF instrumentation available in the MOLAB platform.

 

Technical details

Micro-XRF scanning

The µXRF scanning system ARTAX400 (Bruker) is equipped with a low-power metal-ceramic-type X-ray tube with a Mo anode as the excitation source operating at 50 kV and 700 µA. The system is provided with a Peltier-cooled silicon drift detector (SDD) with an active area of 10 mm2 and a Be window (energy resolution<155 eV at MnKα). The X-ray beam is collimated on the surface with a spot diameter of 650 µm. The distance between the sample and the spectrometer is controlled via a laser diode and is set at 10 mm to allow the analysis of uneven surfaces.  A CCD camera provides a magnified image of the sample region under investigation and allows accurate selection of the measurement position. The measuring head is mounted on a remote-controlled X-Y-Z stage which enables to execute high spatial resolution line-scan and area mapping providing multi-element analyses on areas with maximum dimensions of 50×50mm2. Element distributions across the sample are then originated by dedicated software.

 

Providers

MOLAB Italy: LABDIA

SIRT (Stimulated Infrared Thermography)
Type: Multi/HyperSpectral Imaging

 

Overview

The stimulated Infrared thermography system has been developed by the LRMH and the University of Reims Champagne Ardenne. This instrumentation aims at seeking the state of conservation of different artworks, especially mural painting. It consists on a brief light excitation of the surface in order to look at the heat diffusion to detect defects of the material.

First, the analyzed sample is excited with a flux of photons that produce an increase of the temperature of the area. The variation of temperature leads to a variation of the infrared radiation that is visualized through an infrared thermography camera. The photo-thermal signal depends on parameters governing these physical phenomena: thermal conductivity, thermal emissivity, thermal diffusivity, temperature, specific heat, and density. In addition, theses parameters can be correlated with the following characteristics of the object: aspects of the surface, presence of delamination, presence of cracks, internal structure of the material, progress of a physical and chemical transformation, drying and sedimentation, etc…

For the mapping, the hotter colors reveal warmer spots, which are linked to the presence of an active interface between materials or layers with different properties, for example a void beneath the surface or an interface between two different mortars.

The system can be used as well in a passive way in order to reach the variation of temperature on a surface.

Technical details

It comprises an excitation device, a detection device, and computing instrumentation for monitoring. In order to obtain homogeneous energy deposition, the excitation source is a couple of halogen lamps (Halogen I.R. Ceramic 500 W). This excitation source is modulated, in a pulse way, by means of electronics and of a computing of monitoring. The detection system is constituted of an infrared camera of thermography working in a synchronous way with the excitation system (20 °x 15° /0,3 m Field of view, 1,1 mRad Spatial resolution, 50 mK at 30°C Thermal sensivity, 7,5 to 13 µm Spectral range). Finally, an analysis module completes the system. The measurement can be done in the range of temperature -40°C to120 °C, with 2°c or 2% of accuracy.

Further readings
  1. E. Bernikola, E. Tsiranidou, V. Tornari, V. Detalle, et J. L. Bodnar, « Mapping of defect structural micro-morphology in the documentation of conservation approaches », in Progress in Cultural Heritage Preservation, Springer, 2012, p. 86–96
  2. J. L. Bodnar, K. Mouhoubi, G. Szatanik-Perrier, J. M. Vallet, et V. Detalle, « Photothermal Thermography Applied to the Non-destructive Testing of Different Types of Works of Art », International Journal of Thermophysics, vol. 33, no 10‑11, p. 1996‑2000, nov. 2012
  3. J. L. Bodnar, J. L. Nicolas, J. C. Candoré, et V. Detalle, « Non-destructive Testing by Infrared Thermography Under Random Excitation and ARMA Analysis », International Journal of Thermophysics, vol. 33, no 10‑11, p. 2011‑2015, nov. 2012
  4. Vallet, J.M, Detalle, V., De Luca, L., Bodnar, J.L., Guillon, O.et al“Development of a NDT toolbox dedicated to the conservation of wall paintings: application to the frescoes chapel in the Charterhouse of Villeneuve-lez-Avignon (France),” 2013 Digital Heritage International Congress, Oct 2013, Marseille, France (2013)
  5. Giovannacci, D., Detalle, V., Martos-Levif, D., Ogien, J.,Bernikola, E.,et al., ” Case study of Sainte-Marie Chapel, Fontaine Chaalis (France): complementarity of different optical techniques “, Proc. SPIE 9527, Optics for Arts, Architecture, and Archaeology V, 95270L (July 7, 2015); doi:10.1117/12.2184600; http://dx.doi.org/10.1117/12.2184600
Providers

MOLAB France: CRC – team LRMH

Scanning multispectral VIS-NIR reflectography
Type: Multi/HyperSpectral Imaging

 

Overview

The image analysis offers amazing possibilities for diagnosis and study of artworks. Depending on the type of radiation used (e.g., visible VIS, infrared IR) the different techniques allow us to reconstruct an image of the object that contains information other than that you may have from a simple vision. The results obtained are of extraordinary importance both for the analysis of conservation state of the artwork, and for its storage and memory.

In particular, the Infrared Reflectography, thanks to the properties of transparency of the pigments to the infrared radiation, allows the visualization of features underneath the surface of paintings, such as the underdrawing sketch, the “pentimenti” or subsequent repaintings.

The Multispectral Scanner is revolutionary in the field of infrared reflectography because it allows to simultaneously acquire a set of high resolution images at different wavelengths in the spectral region of near-infrared that are perfectly superimposed and represent the response of the painting at that particular wavelength. The final images obtained with this tool then open up new possibilities of analysis in the field of non-invasive diagnostics, allowing a more detailed study of the materials, of the artist’s technique and of the various phases of preparation of an artwork.

Technical details

The two multi-spectral scanning imaging systems are both evolutions of a prototype developed within the European project EU-ARTECH. The RGB+NIRScannerhas 16 bands: 13 in the near IR covering the range 800-2265 nm, and 3 for acquiring a colour RGB image of the painting;the Vis-NIR Scannerhas 32 bands: 16 in the near IR (800-2400 nm) and 16 in the visible (400-800 nm)range. The spatial sampling is 250 micron and the acquisition speed is 3 hours per square meter for both instruments. Both systems are computer controlled: the instrument softwareconsents the recording of the multi-spectral data setwith real-time monitoring of the acquisition through a user-friendly GUI (Graphic User Interface). The multi-spectral data is stored as aset of 16-bit images, one for each spectral channel.

Further readings
  1. Fontana, R.; Bencini, D.; Carcagnì, P.L.; Greco, M.; Mastroianni, M.; Materazzi, M.; Pampaloni, E.; Pezzati, L.,
    Multi-spectral IR reflectography, proceedings of SPIE, 2007, 6618
  2. Bonifazzi, C.; Carcagnì, P.L.; Fontana, R.; Greco, M.; Mastroianni, M.; Materazzi, M.; Pampaloni, E.; Pezzati, L.; Bencini, D., A scanning device for VIS-NIR multispectralimaging of paintings, «Journal of Optics», 2008, 10 (6)
  3. Daffara, C.; Pampaloni, E.; Pezzati, L.; Barucci, M.; Fontana, R., Scanning Multispectral IR Reflectography SMIRR: an Advanced Tool for Art Diagnostics, «Accounts of Chemical Research», 2010v 43 (6).
Providers

MOLAB Italy: CNR-INO

Vis Hyperspectral Imaging
Type: Multi/HyperSpectral Imaging

 

Overview

The image analysis offers amazing possibilities for diagnosis and study of artworks. Depending on the type of radiation used (e.g., visible VIS, infrared IR) the different techniques allow us to reconstruct an image of the object that contains information other than that you may have from a simple vision. The results obtained are of extraordinary importance both for the analysis of conservation state of the artwork, and for its storage and memory.

In particular, the Infrared Reflectography, thanks to the properties of transparency of the pigments to the infrared radiation, allows the visualization of features underneath the surface of paintings, such as the underdrawing sketch, the “pentimenti” or subsequent repaintings.

The Multispectral Scanner is revolutionary in the field of infrared reflectography because it allows to simultaneously acquire a set of high resolution images at different wavelengths in the spectral region of near-infrared that are perfectly superimposed and represent the response of the painting at that particular wavelength. The final images obtained with this tool then open up new possibilities of analysis in the field of non-invasive diagnostics, allowing a more detailed study of the materials, of the artist’s technique and of the various phases of preparation of an artwork.

Technical details

The two multi-spectral scanning imaging systems are both evolutions of a prototype developed within the European project EU-ARTECH.

The RGB+NIRScannerhas 16 bands: 13 in the near IR covering the range 800-2265 nm, and 3 for acquiring a colour RGB image of the painting;the Vis-NIR Scannerhas 32 bands: 16 in the near IR (800-2400 nm) and 16 in the visible (400-800 nm)range.

The spatial sampling is 250 micron and the acquisition speed is 3 hours per square meter for both instruments.

Both systems are computer controlled: the instrument softwareconsents the recording of the multi-spectral data setwith real-time monitoring of the acquisition through a user-friendly GUI (Graphic User Interface).

The multi-spectral data is stored as aset of 16-bit images, one for each spectral channel.

Providers

MOLAB Italy: UNIPG S.M.A.Art

NIR Hyperspectral Imaging
Type: Multi/HyperSpectral Imaging

 

Overview

Hyperspectral imaging is a chemical imaging technique based on reflectance spectroscopy (the light reflected by materials). This device makes the collection of reflectance spectra in each point of the field of view for the Near Infrared range (it is complementary to another device for the visible range). The hyperspectral image cube obtained can be considered both as a stack of wavelength-resolved images and as a series of spectra.

The near infrared spectra consist of vibrational overtones and combination absorption features where spectral signatures can allow to identify and map different materials.

This technique is well adapted to characterize organic compounds (binding media, plastic materials…) and some minerals.

Hyperspectral Imaging provides spatially resolved information on the nature of chemical species that can be interesting to locate damages (moisture, chemical transformations…), restorations, pentimenti or underdrawings on/in an artwork.

Hyperspectral imaging is well adapted for flat or slightly embossed artworks (manuscript, drawing, paintings,…)

Near Infrared hyperspectral imaging is a non-invasive, in situ technique that allows to collect data cube in few minutes without any preparation of the artwork.

Technical details

The system consists of an ImSpector N25E imaging spectrograph (Specimcorp, Finland) and a cooled, temperature stabilized MCT detector (9.6 mm detector having 320 (spatial) x 256 (spectral) pixels).The camera operates from 970 to 2500 nm with a spectral resolution of 10 nm. It works as a line scan camera providing full, contiguous spectral data for each pixel.

The cooling system (dual Peltier solution, forced convection coolers) is designed to minimize dark current and ensure high stability in the detector operations in a wide ambient temperature range.

Two objective lenses are available:

  • A telecentric lens with a focal length of 15 mm (corresponding to a minimal field of view of 20 cm and a maximal resolution of 600 µm)
  • A macroscopic lens with a 1:1 magnification (corresponding to a field of view of 9.6 mm and a spatial resolution of 30 µm)

The camera is moving along a motorized bar of around 1.6 m, resting on a portal frame structure. The height of the structure is around 2 m. The artwork is illuminated with 6 halogen lamps (three on each side) placed at 45 degrees from the vertical. The current structure is designed to scan artefact laid flat on a tablebut the configuration can possibly be changedto scan artefact in a vertical position.

Further readings
  1. Dooley, K.A., Lomax, S.,Zeibel, J.G., Miliani, C., Ricciardi, P., Hoenigswald, A., Loew, M., Delaney, J.K.,”Mapping of egg yolk and animal skin glue paint binders in Early Renaissance paintings using near infrared reflectance imaging spectroscopy”, Analyst138, 4838-4848, 2013
  2. Ricciardi, P., Delaney, J.K., Facini, M., Zeibel, J.G., Picollo, M.,Lomax, S., Loew, M.,”NearInfraredReflectance Imaging Spectroscopy to MapPaint Binders In Situ on IlluminatedManuscripts”,AngewandteChemie International Edition 51, 5607-5610,2012
  3. Cséfalvayová, L., Strlič, M., Karjalainen H., “Quantitative NIR Chemical Imaging in Heritage Science”, Analytical Chemistry 83, 5101-5106, 2011
  4. Delaney, J.K.,Zeibel, J.G.,Thoury, M., Littleton, R., Palmer, M.,Morales, K.M., René de la Rie, E., Hoenigswald, A.,”Visible and infrared imaging spectroscopy of Picasso’s Harlequin musician: mapping and identification of artist materials in situ”, Applied Spectroscopy 64, 584-94, 2010
  5. Baissa, R.,Labbassi, K., Launeau, P., Gaudin, A., Ouajhain, B.,”UsingHySpex SWIR-320m hyperspectral data for the identification and mapping of minerals in hand specimens of carbonate rocks from the Ankloute Formation (Agadir Basin, Western Morocco)”, Journal of African Earth Sciences 61, 1-9, 2011
Providers

MOLAB France: CRC – Team CRCC

OCT (Optical Coherence Tomography)
Type: 2D/3D Analysis

 

Overview

Optical Coherence Tomography (OCT) originates from diagnostic non-contact and non-invasive techniques in the medical field that can provide information on the internal, sub-surface structure of various objects and which can be successfully applied to artworks. OCT offers a micrometre level in-depth resolution and is well suited for the investigation of fine details of structures which moderately absorb infrared light, such as varnishes, glazes and underdrawings of easel paintings, reverse paintings on glass, glazes on porcelain and faience, jade, historic glass and amber amongst others.

Images obtained by OCT are usually presented in the convenient manner of cross-sectional views, similar to microscopic photographs of cross-sections of samples collected

from the object. If necessary, information of an entire volume (a cube) may be collected by combining together 100 – 200 parallel cross-sections.

The major advantage of OCT is in the complete non-invasive nature of the technique (intensity of light used for examination is in the order of single milliwatts), rapid data collection, and no object preparation. Furthermore the number of measurements across the entire surface can be unlimited, rendering the obtained results much more representative.

Technical details

The instrument (in the figure below) comprises a broad-band light source made up of super luminescent LEDs emitting in a band of 770-970 nm. The intensity of radiation at the object never exceeds 800 μW, and due to fast scanning is focused at any given spot on the object for 40 ms. The axial imaging resolution is 3 μm in air (2/nRμm in a media or refractive index nR), with an axial imaging range of 1.4 mm. The lateral resolution, in the standard configuration, is about 13 μm with a field of view of 17 x 17 mm2 and the distance to the object from the most advanced element of the device equal 43 mm. If necessary, the alternate configuration may be used, providing better resolution (ca 6 μm) but for the price of smaller field of view (5 x 5 mm2) and distance to the object (7.5 mm). The acquisition time of a volume information comprised of 100 cross-sections is ca 12 s.

Further readings
  1. All papers devoted to application of OCT to examination of artworks are listed at www.oct4art.eu.
  2. P. Targowski, M. Iwanicka “Optical Coherence Tomography: its role in the non-invasive structural examination and conservation of cultural heritage objects—a review” Applied Physics A 106(2), 265-277, (2012), DOI: 10.1007/s00339-011-6687-3,
  3. P. Targowski, M. Iwanicka, M. Sylwestrzak, E.A. Kaszewska, C. Frosinini “OCT structural examination of Madonna deiFusi by Leonardo da Vinci“ Proc. SPIE 8790 87900N, (2013), DOI: 10.1117/12.2021607
  4. P. Targowski, M. Iwanicka, B.J. Rouba, C. Frosinini, “OCT for Examination of  Artwork” in: W. Drexler, G. Fugjimoto (Eds.) Optical Coherence Tomography. Technology and Applications, Springer, Cham Heidelberg New York Dordrecht London, 2015, pp. 2473- 2495.
Providers

MOLAB Poland: NCU

THz (Terahertz imaging)
Type: 2D/3D Analysis

 

Overview

Terahertz (THz) spectroscopy and imaging is a non-destructive, non-contact, non-invasive technology emerging as a tool for the analysis of cultural heritage. THz Time Domain Spectroscopy (TDS) techniques have the ability to retrieve information from different layers within a stratified sample. The most explored topics—particularly using time-domain terahertz systems—include stratigraphic examinations of wood panel paintings and plaster-covered wall paintings. However, investigations have expanded to include terahertz imaging of ceramic vessels, corroded metal objects and papyrus sheets.

The data can be displayed through a series of parametric images mapping the imaging area with different arguments as parameters (maximum/minimum amplitude, peak to peak, frequency integration etc.) or as a cross section. In this case, if no sample of the wall material is taken, an assumption must be made on the nature of the material constituting the under-layer to determine the thickness and approximate depth location of the different layers.

Technical details

The technique is based on a compact free-space, time-domain-terahertz reflectometer consisting of an inter-digitated-metal-finger, semi-insulating-photoconductive-GaAs terahertz emitter and a low temperature-grown-GaAs (LT-GaAs) Hertzian-dipole receiver. The mode-locked, two-stage, amplified, Ytterbium fiber laser operates with a center frequency near 1064 nm, a 100 fs pulse width, a 50 MHz repetition rate and a maximum output power of 400 mW. Under laser irradiation a 100fs femtosecond radiated pulses is emitted with a THz frequency component with a usable bandwidth of 2 THz with a dynamic range of >40 dB for minimal averaging. An acquisition rate of 100 Hz is used for a fixed 320 ps measurement window at a 0.078125 ps time resolution. The THz beam emerging from the emitter, is focused using a high density polyethylene (HDPE) lens. The beam is delivered to the object under study, in these examples in reflection geometry. The fiber-coupled antennas permit rapid modification of the measurement geometry which enables easy in situ examinations.

A single THz waveform is digitally acquired and the beam spot is raster scanned across the object. The stages have a coarser 33.3 µm/step resolution, but their maximum speeds are 16 mm/s and 64 mm/s, respectively.

Acquisition time is strongly dependant on the number of averages, the speed of the translation stages and the pixel acquisition rate; these parameters are adjusted to provide the most optimal results for any particular experimental environment. For example a scan of 200 mm by 150 mm, with 50 averages takes around 5 hours.

Further readings
  1. Jackson, J. B., Bowen, J., Walker, G., Labaune, J., Mourou, G., Menu, M., and Fukunaga, K., “A Survey of Terahertz Applications in Cultural Heritage Conservation Science”, IEEE Transactions on Terahertz Science and Technology 1, 220–231, 2011
  2. Walker, G.C., Bowen, J.W., Matthews, W., Roychowdury, S., Labaune, J., Labaune, J., Mourou, G., Menu, M.,Hodder, I., and Jackson, J.B., ―Sub-surface terahertz imaging through uneven surfaces: visualizing Neolithic wall paintings in Çatalhöyük, Optics Express, 21(7), 8126-8134 (2013)
  3. G.C Walker, B. Jackson, D. Giovannacci, J.W. Bowen, B. Delandes, J. Labaune, G.A Mourou, M. Mene, V. Detalle ” Terahertz analysis of stratified wall plaster at buildings of cultural importancesaccross Europe”, SPIE Optical Metrology, 13-16 May 2013, Munich, Proc. SPIE 8790, Optics for Arts, Architecture, and Archaeology IV, 87900H, 8 pages
  4. Giovannacci, D., Martos-Levif, D., Walker, G.C., Menu, M., and Detalle V., ” Terahertz applications in cultural heritage: case studies “, Proc. SPIE 9065, Fundamentals of Laser-Assisted Micro- and Nanotechnologies 2013, 906510 (November 28, 2013); doi:10.1117/12.2049818; http://dx.doi.org/10.1117/12.2049818
Providers

MOLAB France: CRC – Team LRMH

 

DHSPI (Digital Holographic Speckle Pattern Interferometry)
Type: 2D/3D Analysis

 

Overview

Digital Holographic Speckle Pattern Interferometry (DHSPI) is a non-destructive and non-contact optical technique which investigates deformation, deterioration and fracture mechanisms in order to evaluate the structural condition of materials and systems as a result of ageing, mechanical deterioration and materials’ failure. The technique is based on the principles of digital imaging and interferometry and thus it combines the ease of operation and high spatial resolution of digital cameras with the ultrahigh (in sub μm scale) displacement sensing.

The technique enables sensing, detection and documentation of invisible defects, allowing their location, measurement and exact positioning within the structure of the object. Moreover monitoring of structural changes on the basis of environmental and climatic changes, conservation treatments, natural or provoked ageing, transportation or handling, are among the potentials of this technique.

Technical details

The DHSPI-II instrument is a portable custom-made pre-industrial prototype. It has been developed at IESL-FORTH on the basis of experience acquired through the participation within several national and EU projects related with artworks diagnostics. It is a light-weight portable system comprised of an optical head and a control unit.

Optical Head

A 300mW DPSS (Diode Pumped Solid State) 532nm laser with a coherence length higher than 30 m is used for illumination. The output beam divergence is approximately 40cm at 1m. A C-mount lens is used to collect the backscattered light from the object. The field of view (FOV) depends on the lens selection (the FOV for a typical 25mm lens is ~30cm at 1m). The image is captured by a 2 Megapixel CCD and is further processed. This optical configuration provides a sensitivity of 114lines/mm and a displacement resolution of 266nm.

Peripherals: Control unit, software, excitation mechanism, scanning mechanism

The control unit includes all necessary power and control electrics and electronics, as well as a microcomputer that controls all the devices, acquires and processes data. The system is controlled remotely via an external laptop PC while tailor-made operation, processing and post-processing software applications have been developed in LabVIEW environment. The processing software utilizes a step-by-step procedure for easy adjusting the acquisition parameters, capturing and saving data from the camera and the environmental sensors, real-time processing and storage of data and results. The post-processing software contributes to the enhancement and quantification of measurement results, the dimensioning and positioning of structural defects to generate risk-maps.

Further readings
  1. “A new portable Digital Holographic Speckle Pattern Interferometry system for artworks structural documentation”, K. Hatzigiannakis, E. Bernikola, V. Tornari, Lasers in the Conservation of Artworks – LACONA IX proceedings, eds. D. Saunders, M. Strlic, C. Korenberg, N. Luxford and K. Birkholzer, Archetype publications Ltd, London, 210-212 (2013)
  2. “Interference fringe-patterns association to defect-types in artwork conservation: an experiment and research validation review”, V Tornari, E. Tsiranidou, E. Bernikola, Applied Physics A 106(2), 397–410 (2012)
  3. “Rapid initial dimensional changes in wooden panel paintings due to simulated climate-induced alterations monitored by digital coherent out-of-plane interferometry”, E. Bernikola, A. Nevin, V. Tornari, Applied Physics A 95, pp. 387-399 (2009)
  4. “Fully non contact holography-based inspection on dimensionally responsive artwork materials”. V. Tornari, E. Bernikola, A. Nevin, E. Kouloumpi, M. Doulgeridis, C. Fotakis, Sensors 2008, 8, DOI 10.3390/sensors (2008)
  5. “Laser Interference-Based Techniques and Applications in Structural Inspection of Works of Art”, V. Tornari, Analytical and Bioanalytical Chemistry; 387, 761-80 (2007)
Providers

MOLAB Greece: FORTH

NMR Mouse
Type: 2D/3D Analysis

 

Overview

The team at RWTH Aachen University focuses on instrument development and measurement methodology for non destructive testing of objects of art and cultural heritage by Nuclear Magnetic Resonance (NMR) methods. NMR is used to determine molecular structures from chemical shift spectra in chemical analysis and to produce slice-selective images by diagnostic Magnetic Resonance Imaging (MRI) in hospitals. The NMR-MOUSE measures the same parameters as an MRI machine. However, the NMR-MOUSE is portable and provides single-sided access to investigate arbitrarily sized samples at the site.

Technical details

The maximum measurement depth of access for the NMR-MOUSE is 25 mm into the sample without physical contact. Maximum depth resolution of 2.3 μm may be achieved depending on the model of the sensor. With the NMR-MOUSE relaxation rates and signal amplitudes are measured in different types of experiments that give information about the stratigraphy of the object in terms of hydrogen density, volumetric moisture content, translational diffusion coefficient, and moisture flux. 2D relaxation correlation maps are also measured to comment on the pore structure in porous samples. The device can be mounted on a precision sliding table controlled by a stepper motor that positions the device for measurements at different depths. For painted walls and easel paintings horizontal displacements are used while vertical displacements are employed for samples that are placed atop the device. All the equipment may be taken to the measurement site by plane, train and other public transport.

Further readings
  1. B. Blümich, J. Perlo and F. Casanova, Progress in Nuclear Magnetic Resonance Spectroscopy, 2008, 52, 197 – 269
  2. B. Blümich, F. Casanova, J. Perlo, F. Presciutti, C. Anselmi and B. Doherty, Accounts of Chemical Research, 2010, 43, 761–770
  3. D. Capitani, V. Di Tullio, N. Proietti, ProgNucMagnResonSpectr., 2012, 64, 29–69
  4. B. Blümich, S. Pholemeir, W. Zia, Compact NMR, De Greuyter, 2014
  5. K. Fukunaga, T. Meldrum, W. Zia, M. Ohno, T. Fuchida, B. Bluemich, Digital Herit. Int. Congr 2013, 1, 81–88
Providers

MOLAB Germany: RWTH 

 

AFM (Atomic Force Microscopy)
Type: 2D/3D Analysis

 

Overview

AFM is a scanning probe technique used for high-resolution surface investigation at the micrometre and nanometre scale. It involves scanning a probe tip situated on the end of  a flexible cantilever across the sample surface and  measuring the attractive or repulsive forces between the  tip and the sample. AFM is capable of acquiring images with little or no sample preparation and is particularly suited for the generation of images indicating changes in surface roughness, of pigment particle size differences, polymer films, binder compositions, dispersing agents, surfactants etc.  For paint films it can offer indicators of degrade due to morphology changes as well as surface modifications on wet-surface cleaning treatments.

Technical details

Images are collected with a nanosurf easyScan DFM.  Scans are made using a POINTPROBE Silicon SPM- Sensor, Al-coating cantilever (nanoworld). The scans can be treated and analysed with SPIP software (Image Metrology) and reported in 3D visualization in grey scale, where the darker colours correspond with deeper regions and bright colours with higher regions.

In situ measurements (as observed below) can be collected by positioning an artwork in a supported horizontal position minimizing vibrational noise as much as possible, and the AFM scan head (weight 350g)  can be carefully placed onto the surface. In the absence of more sophisticated vibration damping methods in the instrumental set-up, the AFM images obtained from these tests included vibration-derived artefacts, which are visible as banding patterns.

Further reading

E. Kampasakali, B. Ormsby, A. Cosentino, C. Miliani, T. Learner, A preliminary evaluation of the surfaces of acrili emulsion paint films and the effects of wet-cleaning by Atomic Force Microscopy (AFM), Studies in Conservation, 56 (2011) 216-230

Providers

MOLAB Italy: UNIPG S.M.A.Art

Confocal OCT microscope
Type: 2D/3D Analysis

 

Overview

When investigating the aging process of old paintings, it is of great importance to obtain insight into the painting technique as practiced in the past, and the first step in gaining this knowledge is, to a large extent, based on the study of the varnish film. Besides that, measuring the varnish thickness is often the starting point of the cleaning operation, the process whereby materials are selectively removed from a painted surface by partial thinning or complete elimination of varnish, being, thus, an irreversible process which may result in chromatic and morphological variations of the painted surface.

OCT is an interferometric technique whose output is a high-resolution stratigraphic image of the examined surface resulting in a visual and numerical quantification of the varnish layer thickness.

The prototype combines confocal microscope optics with the OCT-technique set-up: confocal operation allows to set the beam focus position inside the sample. The excessive reflectance of some of the varnish layers, that  may cause a signal intense enough to cover the one produced by interfaces at deeper levels, can be bypassed by displacing the beam focus inside the sample rather than on the outer surface.

Technical details

The confocal OCT microscope is based on an optical-fiber interferometer that uses a low-coherence source at 1550 nm, with 100 nm FWHM spectral band.

The instrument has a working distance of about 3 mm. The maximum scanning length (y direction) is 25 mm (about 20 min for a single tomographic section). The lateral resolution is about 2.5 micron. The dynamics, that is the axial length (z direction) along with the instrument  yields tomographic results, is 1 mm and the axial resolution is less than 10 micron in air.

Many profiles can be acquired along the x direction to acquire a tomocube, whose maximum dimension is 1´1 mm with a sampling step of 10 micron, due to the huge dimension of the output data (nearly 2 hours).

The instrument (see pictures below) needs a stable positioning to work properly.

Further readings
  1. G. Latour, J.P. Echard, B. Soulier, I. Emond, S. Vaiedelich, M. Elias, Appl. Opt. 48, 6485 (2009)
  2. P. Targowski, M. Iwanicka, L. Tyminska-Widmer, M. Sylwestrzak, E.A. Kwiatkowska, Acc. Chem. Res. 46, 826 (2010)
  3. H. Liang, B. Peric, M. Hughes, A.G. Podoleanu, M. Spring, S. Roehrs, Optical coherence tomography in archaeological and conservation science—a new emerging field. Proc. SPIE 7139, 713915 (2008).
Providers

MOLAB Italy: CNR-INO