The patented Matisse System to prevent deterioration of works of art

Author: Vicente Galdon
Date 01/09/2023

Author’s note: The Spectral Analysis System for the conservation of works of art and cultural heritage, also known as the “Matisse Method” was presented to the scientific community at the XIX Restoration Congress held in 2018 at the National Art Center Museum Queen Sofia. In this entry, we reproduce the publication as it was published in the minutes of the Congress.

Authors

MICHEL SILVA FINO / TERESA CONTELL VILLAGRASA / ÁLVARO M. PONS MORENO / DANIEL CÁMARA ALBEROLA / MARIA TERESA MARTÍNEZ LÓPEZ / SERGIO RUBIRA

Summary

This work presents the protocol of a research project whose objective is to develop a lighting prototype using LED technology, which improves the current lighting conditions common in exhibition halls of works of art by applying methodologies that use characteristics of visual perception. .

To this end, the Department of Optics, Optometry and Vision Sciences of the University of Valencia, the Departments of Maintenance and Restoration of the IVAM and the museum lighting company MATISSE LIGHTING S.L. They propose applying innovative tools and the latest technologies that generate proven energy savings, respect the conditions of preventive conservation and improve the quality of lighting of works of art for the enjoyment of users of museums and institutions linked to historical-artistic heritage.

Introduction

In 2004, the Commission Internationale de l’Eclairage (CIE) published the technical report 157-2004 Control of damage by optical radiation to museum objects1, which establishes lighting protocols for artistic works, which are defined from a balance between the problems derived from the photochemical action of radiation and the problems of chromatic fidelity of the visualization of the work. This widely accepted standard does not take into account the rapid incorporation of solid state illuminants (Light emitting diode, LED), driven by both environmental and energy saving issues, which have given rise to different legislations that establish the prohibition of their use. of certain illuminants common in museums2,3.

The introduction of this type of lighting presents many advantages: on the one hand, the restriction to the visible range of the optical radiation spectrum of the LED4 avoids not only the problems derived from the ultraviolet (UV) and infrared (IR) range tails that other illuminants had, such as those based on incandescent or halide lamps, but it favors optical measurement processes by being able to use conventional photometry and not radiometric measurement systems. In this way, the necessary assumption of the component contributed in each UV or IR range per lumen of visible illumination, which obviously does not have to be fulfilled in the daily reality of lighting processes, is minimized.

In a recent work, Szabo and Schanda5 concluded that LED lighting of works of art is one of the safest ways from the point of view of preserving the work of art.

However, the use of LEDs is not without problems: although, obviously, the practical absence of a UV component means that the lighting can acquire higher values than with other illuminants, the emission spectrum of white light LEDs, in general formed by RGB clusters or by phosphorescent hoods, can give rise to two important problems: on the one hand, the strong component in the visible blue band of this lighting is very energetic, so it can give rise to photochemical reactions and, on the other hand, , the low quality of color reproduction compared to tungsten or halogen lamps, which can hinder the ability of the human eye to perceive color differences. The works of Mahler et al.6, van der Burgt and van Kemenade7, and Ohno4 generally describe the low values of the CIE color rendering index (CIE-CRI) [F.01].

These two objections are easily circumvented with current technology: the new LED lighting systems allow a modification of the emission spectrum that reduces the blue component or even adapts to more comfortable visual characteristics, for example, a lighting temperature of correlated color of 5500K as proposed by Nascimento and Masuda8, even favors adaptation to the pigment absorption spectra of the works to minimize damage9. This modification can be made by improving the correct color reproduction according to established metrics such as CIE TC 1-903, CIE CRI2012 model162 or through the proposal of corresponding color color rendering (CCCR) proposed in the Schanda study10,11.

Características específicas de la iluminación LED

Actualmente, la mayoría de museos emplean antiguas tecnologías para la iluminación artificial de sus instalaciones y obras, siendo las más extendidas el halogenuro metálico y el foco halógeno, cuya fabricación está prohibida desde junio de 2017. El motivo por el que este tipo de lámparas aún se emplean es, principalmente, por su accesibilidad y por el refrendo científico establecido¹.

Desde el punto de vista de la reproductibilidad cromática, se caracterizan por su elevado Índice de Reproducción Cromática (CRI): entre 98 y 100 en el caso de los focos halógenos y entre 65 y 95 en el caso del halogenuro metálico. Como ya se ha indicado, los valores de CRI obtenidos por los sistemas LED fueron inferiores, por lo que los conservadores y responsables de las exposiciones de los museos evitaron cambiar de tecnología ante la falta de datos. Hoy en día, es fácil encontrar en el mercado sistemas LED con valores de CRI superiores a 95, pero todavía no se encuentran muchas pruebas en la literatura científica con estos sistemas¹², pese a la evidente necesidad de revisitar la regla de Kruithof¹³.

Los criterios de iluminación que predominan en el mundo del arte están sujetos a las recomendaciones publicadas por Consejo Internacional de Museos (ICOM), el Comité Internacional de Iluminación (CIE) y la Illuminating Engineering Society (IES), en las que se establecen preferentemente las pautas sobre sobre temperaturas de color e iluminancias adecuadas para evitar efectos perjudiciales en las obras [F.02, 03 y 04].

F.02 Maximum recommended illuminance levels.
Group	Materials	Illuminance (lx)
A	Acuarelas, telas, papel, grabados, etc.	50
B	Óleos, témperas, hueso, marfil, cuero, etc.	200
C	Piedra, metal, cerámica, fotos en blanco y negro	300

F.03 Recommended maximum cumulative exposure values.
Group	Materials	Values (lx·h/año)
A	Acuarelas, telas, papel, grabados, etc.	50.000
B	Óleos, témperas, hueso, marfil, cuero, etc.	600.000
C	Piedra, metal, cerámica, fotos en blanco y negro

F.04 Deterioration factors and CCT of some light sources
Source	Fd	CCT (K)
Sodio blanco	0.1	2500
Lamp. Incandesc	0.15	2800
Halógena (abierta)	0.2	3000
Mastercolour (HM)	0.2	3000
Inducción QL	0.2	3000
Tubos fluorescentes
color 84	0.21	4000
color 94	0.18	3800
color 96	0.34	6500
Luz diurna	0.68

Although there are some works that already try to optimize LED lighting based on color appearance parameters11,14, their applicability is limited by the use of the CIECAM02 space and the use of very limited samples of the color palette of the work. Furthermore, these works do not take into account the implications for the conservation of the work derived from the color palette of the work itself: if the distribution of colors is very dark, generally and depending on the pigments, the energy absorption in the band visible will be greater, so it is essential to also adjust the energy bands that the work will absorb from the illuminant.

How the Matisse method works

The Matisse Method proposed in this work consists of a non-invasive test that is carried out on the work of art. In the case at hand, it has been applied to a work that belongs to the IVAM Collection: The Beach, by Karel Apple, made in oil on canvas in 1955 and with dimensions of 97 x 130 cm.

For its initial study, the work was illuminated with a track spotlight, which mounts a halogen lamp of between 70 and 100W power. It must be taken into account that the radiometric distribution of this type of illuminants is strongly biased, with an important emission component in the infrared radiation (IR) band, which constitutes more than 80% of the energy emitted by the lamp [F. 05].

In figure [F.04] you can see how the wavelength components close to 780nm predominate, where the limit of human perception is located. Beyond that point, the radiation emitted (called infrared) is harmful to the conservation of works of art, as indicated in the CIE 2004 standard. On the other side of the graph we have ultraviolet (UV) radiation, they are located in the shorter wavelengths, but higher energy. Here halogen technology does not present major problems, because its UV emission is low compared to other radiations, but other technologies commonly used in museums do not share the same characteristic, such as fluorescents, Metal Halides, and in rare cases Xenon lamps, devices in which UV radiation emissions are not negligible [F.06].

Light source	UV (μW/lm)
Luz solar	400 – 1500
Incandescente tungsteno	70 – 80
Halógeno tungsteno	40 -170
Lámpara fluorescente	30 – 100
Halogenuro metálico	160 – 700
LED	<5

Figura 4

Test methodology

For the test carried out, the experimental setup shown in figure [F.06] was set up. In front of the object under study (OBE), a variable LED luminaire and the ASENSETEK PRO STANDARD spectrolorimetric measurement systems [F.07] are installed.

The main feature of the LED luminaire is its ability to vary the light parameters: spectrum, color temperature, color rendering index, color coordinates in the color space, etc. The luminaire is controlled from a laptop computer, which has software specially developed for the process and a communication bus that allows programming light profiles and making the luminaire reproduce them with high precision. Additionally, the luminaire has an optical system that allows us to control the angle and shape of the light beam, which allows the test methodology to be adapted to works of different shapes, dimensions, and proportions.

The spectrocolorimetry equipment is arranged at the appropriate distance from the OBE so that the probe subtends the appropriate measurement angle for the sample, with the purpose of reading the light reflected by the OBE that arrives from the LED luminaire. For the development of the protocol, the following parameters will be determined: color temperature, chromatic coordinates in the CIE1931 and CIE1976 color spaces, Color Rendering Index (CRI), Purity, Illuminance, dominant wavelength, flicker and spectral distribution.

The basic premise of the Matisse Method is the comparison between the emitted light and the reflected light: once determined, the average absorption spectrum of the OBE can be calculated. Since the IR and UV emissions of the LED are negligible, only the visible range of the spectrum will be used, considered from 380nm to 780nm in coincidence both with the photopic sensitivity curve of the standard observer proposed by the CIE (1924) and with the emissions range of LED technology.

First, the lighting will be optimized based on the color temperature of the LED illuminant, for which a progressive scan is carried out at different color temperatures, between 2300K and 8000K. In this scan, the color temperature that maintains the reference white more unaltered in the CIE XY chromatic diagram is determined, also determining which is the color temperature that the OBE reflects the most light, which will be considered as illumination temperature. In a second optimization step, the chromatic reproducibility is improved, through a library of lighting profiles that reproduce the color temperature obtained [F.08].

In figure [F.08] you can see how to obtain light profiles within the same color temperature 4000K, where at one end we have yellow/green tints and at the other end we will have pink/blue tints. Despite being the same color temperature, the differences in the two light profiles are very evident. At first glance, its notable chromatic differences can be seen; consequently, its effect on an illuminated element is also an object of consideration.

With this procedure, the reflectivity of each light profile measured over the same color temperature is evaluated, until a point is obtained where the best possible response is given. That point, which turns out to be a light profile optimized for the conservation of the OBE, will be taken as a central part of a final measurement process, which is carried out by making small changes in the parameters of the variable luminaire to make the light have tendencies towards different directions in color space, starting from that central point.

Each time a light profile is projected onto the OBE, records are taken with spectrophotocolorimetry equipment for subsequent analysis.

Human photopic response

Conservation is one of the two axes of the Matisse Method, which is resolved by seeking the optimized light profile, the point at which the work returns the greatest amount of radiation projected onto it. The other axis is the correct visualization of the work, which is achieved from the comparison of the optimized light profile with the photopic spectral sensitivity curve of the standard observer V(λ) proposed by the CIE, which defines the average photopic response of the human eye under photopic illumination conditions. This curve, defined by the CIE in 1924, establishes the relative efficiency of illumination as a function of wavelength, establishing a maximum around 555 nm, as shown in figure [F.09]15. This curve is the basis for the definition of any colorimetric system16.

The final result of the analysis allows us to find in the color space a point close to the optimized light profile, in which the light has the most appropriate characteristics based on the human photopic response.

Practical application

The Matisse Method is developed as a directly applicable methodology, with technical feasibility and applicability. Therefore, once the data resulting from the analysis is obtained, it is structured in such a way that it will allow us to find an LED on the market that meets the needs of the OBE, both for visualization and conservation. The last step is therefore to search the market for an LED system that meets the requirements, or if it is not available, to be able to generate the LED from an additive synthesis method using a cluster of LEDs. This method consists of obtaining a specific light spectrum through the addition of monochromatic components and white light, so that it is possible to change the spectral components of the lighting. Thus, for example, given a 4000K white LED, it can be modified towards the blues of the chromatic diagram by adding the component of a blue LED, which will increase its color temperature. With this generic method you can modify the spectrum by adding spectral components of any type, from blues, reds, purples or yellows. If an LED cluster is programmed with the desired characteristics, it will be possible to subsequently install it in a luminaire applicable to a museum space, such as a track spotlight, a recessed spotlight, or a wall washer.

Conclusions

Preventive conservation constitutes a valuable tool for conservation-restoration professionals, and technicians associated with them, to avoid deterioration and damage to collections belonging to artistic heritage as it establishes a work plan that designs and plans certain action protocols17, 18.

One of the determining factors that are valued in these actions is the degrading action of lighting on the works of art, which must be illuminated for viewing by visitors and, at the same time, protected from the incidence of light radiation. depending on the time of exposure to it, the intensity of the radiation supported, the characteristics of the lighting sources and, finally, the materials that make up the works of art19,20.

The advancement of LED technology can add value to preventive conservation processes given that its IR and UV radiation is negligible. This makes some current criteria such as the recommendation of maximum illuminances on the work obsolete and require a review, since the radiometric components in the IR and UV bands are determined based on the photometric components, which are easier to determine, given the distributions of the usual light sources.

The proposed Matisse Method makes it possible to reduce harmful radiation for works within the visible spectrum. It is a flexible method that allows us to prioritize visualization or conservation, as well as increase the illuminance values of a work far beyond the regulatory limits defined with other types of illuminants that are contemplated in some museums, with the assurance that we are not adding factors. to the deterioration of works of art.

Image references

[F. 01]

Spectral distribution of different LED sources 4. Source: Y. Ohno, “Color Rendering and Luminous Efficacy of White LED Spectra”, Proceedings of SPIE, Fourth International Conference on Solid State Lighting, Denver Colorado, Bellingham, Washington, SPIE, 2004, 5530 , pp. 88–98.

[F.02]

Recommended maximum illuminance levels.

[F.03]

Recommended maximum cumulative exposure values.

[F.04]

Deterioration factors and color temperature of some light sources.

[F.05]

Illuminated work and spectrum of halogen lamp used. Images generated during the process of applying the Matisse Method.

[F.06]

Ultraviolet radiation per lumen emitted by different light sources. Source: International Commission on Illumination, “Control of damage to museum objects by optical radiation”, CIE Technical Report 157:2004, pp 5.

[F.07]

Arrangement of the equipment and the object under study. Matisse Method, https://matisselighting.art

[F.08]

Two points far apart in color space that share the same color temperature. Own elaboration.

[F.09]

Photopic visibility curve V(l) for the standard observer. Fundamentals of colorimetry. Valencia: Publications of the University of Valencia, 2002.

Bibliographic references in the text

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Commission Internationale de l’Eclairage, “A Colour Appearance Model for Colour Management Systems: CIECAM02”, CIE Publication 159:2004, Vienna, CIE, 2004.
Commission International de l’Eclairge, “On the Deterioration of Exhibited Museum Objects by Optical Radiation”, CIE Publication 89-1991, Vienna, CIE, 1991.
Ohno, “Color Rendering and Luminous Efficacy of White LED Spectra”, Proceedings of SPIE, Fourth International Conference on Solid State Lighting, Denver Colorado, Bellingham, Washington, SPIE, 2004, 5530, pp. 88–98.
Mahler, J.J. Ezrati y F. Viénot, “Testing LED Lighting for Colour Discrimination and Colour Rendering”, Color Research and Applications, 3, 2008, pp. 8–17.
Szabo y J. Schanda, “Solid state light sources in museum lighting – lighting reconstruction of the Sistine chapel in the Vatican”, Proceedings of the CIE 2012 Lighting Quality and Energy Efficiency Conference, Hangzhou, CIE Publication x037, 2012, pp. 256–263.
van der Burgt y J. van Kemenade, “About Color Rendition of Light Sources: The Balance Between Simplicity and Accuracy”, Color Research and Applications, 35, 2010, pp. 85–93.
M.C. Nascimento y O. Masuda, “Best lighting for visual appreciation of artistic paintings experiments with real paintings and real illumination”, Journal of the Optical Society of America A, 31, 2014, A214–A219.
F. Delgado, C.W. Dirk, J. Druzik y N. WestFall, “Lighting the World’s Treasures: Approaches to Safer Museum Lighting”, Color Research and Applications, 36, 2011, pp. 230–254.
Schanda, P. Csuti y Szabó, F. “A New Concept of Color Fidelity for Museum Lighting”, LEUKOS, 00, 2014, pp. 1–7.
Schanda, P. Csuti y F. Szabó, “Colour fidelity for picture gallery illumination, Part 1: Determining the optimum light-emitting diode spectrum”, Lighting Res. Technol, 47, 2015, 513–521.
Piccablotto, C. Aghemo, A. Pellegrino, P. Iacomussi, et al., “Study on conservation aspects using LED technology for museum lighting”, Energy Procedia, 78, 2015, pp. 1347–1352.
Viénot, M.L. Durand, y E. Mahler, “Kruithof’s rule revisited using LED illumination”, Journal of Modern Optics, 56, 2009, pp. 1433–1446.
Csuti, A. Fa´y b, J. Schanda, F. Szabo, et al., “Colour fidelity for picture gallery illumination, Part 2: Test sample selection – museum tests”, Lighting Res. Technol, 46, 2014, pp. 1–11.
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