Alexandra Marco, Joaquim Inácio Caetano, Eduarda Vieira, Manuela Pintado, Patrícia R. Moreira, Chromatic alterations in 15th and 16th century fresco paintings in northern Portugal, e-conservation Journal 6, 2018/2019
doi: pending

Chromatic alterations in 15th and 16th century fresco paintings in northern Portugal

Alexandra Marco1,2,3, Joaquim Inácio Caetano4, Eduarda Vieira1,2,
Manuela Pintado3, Patrícia R. Moreira1,2,3

1 School of Arts, Portuguese Catholic University. Rua Diogo Botelho 1327, 4169-005 Porto, Portugal
2 CITAR – Research Centre for Science and Technology on Arts, Portuguese Catholic University. Rua Diogo Botelho 1327, 4169-005 Porto, Portugal
3 CBQF – Centre for Biotechnology and Fine Chemistry, Portuguese Catholic University. Rua Arquiteto Lobão Vital 172, 4200-374 Porto, Portugal
4 ARTIS – Art History Institute, Faculty of Arts and Humanities of Lisbon University (FL-UL). Alameda da Universidade, 1600-214 Lisboa, Portugal



In the course of extensive cataloguing of wall painting ensembles in northern Portugal, a problem of biodeterioration featuring abundant production of a black colour film that stains both the granite wall and the painting is often encountered. Although the visual impact resulting from this alteration is a matter of importance in the aesthetic restitution of the painted surfaces, their stain removal is practically impossible. Whereas the microbial charge reduction is usually achieved through the use of biocide treatment, these products are unsuccessful in removing the dark pigmentation resulting of their growth. Despite frescoes’ substrate being mainly inorganic, deposition of atmospheric particles and the absorption of water by capillarity can promote the development of fungi, which secrete metabolites such as organic acids. Several fungi also produce pigments that vary depending on the species, the constituents of wall painting and environmental factors, among others. To ascertain how do the stains appear and what are the common characteristics between the monuments and their paintings that allow fungi growth, 24 Romanesque churches with 15th and 16th mural painting sets were selected. For this study, each mural painting was analysed and a series of variables collected for evaluation. While a great number of variables are amiss, the ones gathered underline that the majority of the churches presenting such stains are small, located on lowland, in the countryside and in isolated surroundings. Their orientation is mainly West-East, and date from 10th to 13th centuries while the wall paintings are mostly from the 15th-16th centuries. The chromatic alterations seem to appear when the paintings are uncovered from behind mortar and altars during conservation works.

1. Introduction

Although much of the studies of Portuguese mural painting are yet to be done, it is well known that this artistic expression was developed in Portugal with intense activity between the 15th and 16th centuries [1, 2]. According to Sousa [3], this pictorial genre reappeared at this time in Portugal brought by foreign painters working here, national painters with international experience, and through the acquaintance of examples in the Iberian Peninsula.

Due to the technical differences of the various painting centres, Caetano [2] divided Portugal into two main geographical regions based on the number of plaster layers, even though this division is not binding. In this way, from the Southern regions up to Coimbra, fresco painting was characterized by at least two layers of mortar. In the North, the mural painting shows only one layer of mortar without any ground layer, directly applied onto the support (Fig. 1).

Concerning material sources, the northern region is mostly granitic and the production of lime was scarce. In the northern municipalities of Bragança and Vinhais, there were limestone outcrops which were numerous but limited in terms of extractive amounts [4]. In Serra do Marão there was also an important limestone outcrop, though of small dimensions [2], and limestone furnaces of Roman typology were discovered in Salselas (Macedo de Cavaleiros) and Louredo (Santa Marta de Penaguião) [5]. These regional constraints affected the way the pictorial technique was adapted in the region [6]. However, the lime characteristics appear to be identical – a hydraulic lime, due to the high content of impurities, cohesive and resistance. The support of these paintings was almost exclusively granite, a rock with good physical-chemistry properties for the execution of lime coatings and related decorative types.

From the technical point of view, the wall paintings can be executed in tempera, fresco, and fresco with a secco finishing [2, 7]. They are mostly composed of inorganic materials (pigments, mortars, and stone or brick support) and, in lower quantity, organic materials (binders). The scope of the use of organic materials varies according to the painting technique, the period, and the artist’s intention [8]. The colour palette is restricted. Typically, the pigments are of mineral origin: calcium carbonate or sulphate (CaCO3 or CaSO4) for white; natural and burned ochre for yellows and reds; earth for reds and greens; raw or burnt umber for browns; and ivory, bone or vine black for black pigments [9].

Besides human action, the degradation of wall paintings is related to the porosity of the substrate, its carbonated nature, presence of water in the walls, and environmental conditions [10]. The conjugation of these agents is responsible for the significant loss of pictorial area and dark pigmentation due to biocolonization. In northern Portugal, several 15th-16th century frescoes show this alteration that stains both the supports and paintings, a change of great aesthetic impact that dominates the attention of conservators-restorers in the methodology of their interventions (Fig. 2). To ensure ethical and sustainable interventions, it is essential to know both the nature and behaviour of materials, their current conservation status, and the identification of agents and degradation factors.

This study focuses on perceiving how the wall paintings’ chromatic alterations are related to the presence and growth of microorganisms (mainly fungi), including the commonality aspects regarding wall paintings in religious buildings in northern Portugal, which makes them susceptible to fungi degradation. The future aim is to isolate the compounds responsible for the production of the dark coloured stains and to eliminate or attenuate their visual impact on mural paintings. Some assays were already performed [11].

In this sense, a large number of churches with mural paintings is being studied in order to understand the relationship between their discovery and the development of biodegradation by fungi in the form of dark anaesthetic stains.

Left to right:
Figure 1. Fragment of 15th century mural painting in Parish Church of S. Tiago, Baião. Example of how thin are the layers in northern Portugal, and the existence of only two layers – pictorial layer and only one layer of mortar applied directly onto the granite support.

Figure 2. “Pentecostes” 16th century mural painting in Santa Eulália Church, V. N. Famalicão. Dark stains appearing on the wall years after the removal of the altars.

2. Materials and Methodology

As summarized in Table 1, a total of 24 churches were surveyed: one in central Portugal and 23 in northern Portugal.

A series of data, comprising variables concerning geography, monuments’ characteristics, and wall paintings’ characteristics, was collected and organised in tables. Some of this information was collected from online built heritage information systems such as the Information System for Architectural Heritage (SIPA) [12], and the General Directorate of Cultural Heritage (DGPC) [13], General Directorate of National Buildings and Monuments (DGEMN) Bulletins, as well as from other documental sources [2, 3, 6, 14-16].

Geographical information of the churches’ neighbourhood includes the orientation, location (lowland or highland), environment surroundings (urban or countryside; isolated or in mist of village), and proximity to graveyards and waterways. As for the monuments’ characteristics it includes data such as the type of protection (by the state, parish or private), construction date, scale and number of divisions, construction materials (type of granite grain), the exterior and interior joint materials, number and location of windows, and location of the dark stains on granite.

Concerning the wall paintings themselves, information on their characteristics was gathered, namely the century they were made, materials, location by wall and by cardinal points, location of the dark stains, eventual restoration interventions, and whether they are exposed to the environment or covered by mortar or/and altars.

A map was created to pinpoint the location of each monument using Google Earth (Fig. 3). Due to the nature of this ongoing research, and the large number of data collected so far, here we focus on the region that has more information gathered until now: Douro Litoral region.

Figure 3. Satellite map pinpointing the location of the six churches case studies
in the Douro Litoral region. © 2018, Google earth.

3. Results and Discussion


The data of these case studies were compiled and condensed into tables, separated by geography (Table 2), monuments’ characteristics (Table 3) and wall paintings’ characteristics (Table 4). The full list of the churches can be seen in Table 1.

The data in the form of variables was gathered in order to perceive the churches’ common features and to establish the causes for the appearance of chromatic alterations. We established the amount of information necessary to obtain some insights, within reasonable access and easiness of retrieval.
At the moment there is still a large amount of information lacking. However, with the available information it is perceived that the majority of the churches are of medium size (2 or 3 volumes such as aisle, presbytery and sacristy), located on lowland, in the countryside and isolated surroundings. Their orientation, apart from two with other exposure and several yet unknown, is West-East. The churches are Romanic fabric (from 10th to 13th centuries) and the wall paintings are mostly from the 15th-16th centuries. If they had not suffered interventions in the 20th or 21st century, the joint materials are probably still in lime. The discovery of the wall paintings was mainly in the 1950s and 1960s, when the puritanism led to strip the churches of ulterior embellishments. The paintings were behind altars and some covered by mortar. Those covered with mortar and altars seem to be free of chromatic alterations. Though, once placed in view, the stains appear as observed in pictures just after removal and years later.

Some of the data recollection has proven to be difficult, missing several elements such as the number of windows in the monuments, the existence of water flows, cemeteries nearby, tombstones with skeletons inside the churches, and the carried out interventions, among others.  Other information has also been lost or misplaced such as that gathered by Joaquim Inácio Caetano and Catarina Vilaça in their wanderings into the territory documenting the existence and state of mural paintings and deposited in Forte de Sacavém, or Abel de Moura’s 20-year Gulbenkian research grant that should have resulted in an inventory of Portuguese mural painting but was never published and is nowadays lost. This information may be crucial to answer the question of how and why do the dark stains appear, since it should contain data regarding conservation state and photographs evidencing the non-existing stains or their early stages timed.

For further work, the climate conditions (namely external temperature and relative humidity) will be measured for long-time periods to understand its variations, with the aid of the Portuguese Institute for Sea and Atmosphere (IPMA). Furthermore, an evaluation of the buildings’ interior and surroundings, is to be assessed onsite. Also, the detection of water sources is crucial to ascertain the degree of humidity on the walls.

In addition, it came to our knowledge that a wall painting recently discovered and treated (in northern Portugal) has no chromatic alterations. This painting will be an effective case study to determine if and when the stains occur and evaluate the assumptions made regarding the main factors for the appearance of the stains.

Table 1. List of the 24 churches in this study.

Table 2. Variables regarding the geography of the terrain in each of the churches from the Douro Litoral region.

Table 3. Variables regarding the characteristics of the monuments/churches from the Douro Litoral region.

Table 4. Variables regarding the characteristics of the wall paintings in each of the churches from the Douro Litoral region.

4. Conclusions

During conservators’ and historians’ extensive fieldwork in the 1970’s in Portugal, several mural painting ensembles were rediscovered and catalogued by the mural painting’s division of José de Figueiredo Institute (IJF) under coordination of Abel de Moura. Regardless of this extensive survey along with many other personal contributions in the basis of several publications and thesis some information was never catalogued or stored in one single facility for easy access. Although there is an amount of information already collected, we came across an official absence of elements imperative to the investigation, in terms of the monuments and their structures. Thus, there is a need to fill in the underlined gaps such as tutelage, cleaning, and cult frequency or lack of it, state of conservation, previous interventions, possibility of organic matter existence in the indoor tombs, presence of salts, presence of water nearby, among others, either by consulting official sources or by an in situ inspection and monitoring.

Through the gathering of the missing information, and the recent case of mural paintings rediscovered without the presence of stains in them, allows us to perceive what conditions are essential for their appearance and how long it could take.

With this project we hope to find a solution for the chromatic alterations on wall paintings, minimizing their visual impact without damaging the 500-year-old paintings.

5. Acknowledgments

This research was carried out as part of the first author PhD research funded by a grant from Fundação para a Ciência e Tecnologia (FCT) (SFRH/BD/125596/2016) and through the project BIO4MURAL – Soluções inovadoras de biotecnologia para remoção de pigmentação e conservação preventiva de pintura mural cultural e historicamente relevante, supported by FCT and Programa Operacional Competitividade e Internacionalização (FEDER) (PTDC/HAR-ARQ/29157/2017).

6. References

[1] D. Rodrigues, A Pintura Mural na Região Norte. Exemplares dos séculos XV e XVI, in: A Colecção Pint. Do Mus. Alberto Sampaio Séculos XVI-XVIII, Instituto Português de Museus, Lisboa, 1996

[2] J.I. Caetano, A pintura a fresco e as suas características técnicas. O caso dos exemplares dos séculos XV e XVI no Norte de Portugal e sua conservação, Revista Guimarães, 2001, pp. 199–217

[3] C.V. de Sousa, A pintura mural na região de Guimarães no século XVI, Revista Guimarães, 2001, pp. 219–273

[4] A. Redentor, A produção tradicional de cal no extremo setentrional dos Concelhos de Linhais e Bragança: Contributo para o seu estudo, Brigantia. XXIII, 2003, pp. 37–62.ção_tradicional_de_cal_no_extremo_setentrional_dos_concelhos_de_Vinhais_e_Bragança_contributo_para_o_seu_estudo (accessed 21 September, 2015)

[5] M. Lacerda, Na perspectiva do tempo, Estudos/Património 3, 2002, pp. 5–7. (accessed 14 April, 2014)

[6] J.I. Caetano, O Marão e as oficinas de pintura mural dos séculos XV e XVI, Colecção Estudos de Património Cultural 1, 2001

[7] J.G.R. Henriques, A Charola de Tomar. Estratégias de conservação da pintura mural, Dissertação de Mestrado, Faculdade de Letras de Lisboa. Universidade Clássica de Lisboa, 2000

[8] F. Rosi, A. Daveri, C. Miliani, G. Verri, P. Benedetti, F. Piqué, B.G. Brunetti, A. Sgamellotti, Non-invasive identification of organic materials in wall paintings by fiber optic reflectance infrared spectroscopy: a statistical multivariate approach, Analytical and Bioanalytical Chemistry 395, 2009, pp. 2097–2106. doi:10.1007/s00216-009-3108-y

[9] F.R. Presenti, El fresco, in: C. Maltese (ed.), Las Técnicas Artísticas, 9th ed., Ediciones Cátedra, S.A, Madrid, 1997

[10] M.P. Nugari, M. Realini, A. Roccardi, Contamination of mural paintings by indoor airborne fungal spores, Aerobiologia 9, 1993, pp. 131–139, doi:10.1007/BF02066254

[11] A. Marco, P.R. Moreira, M. Pintado, E. Vieira, Enzymatic degradation of fungal pigmentation from wall painting’s isolates, COLOR research and application 41, 2016, pp. 299–301. doi:10.1002/col.22025

[12] SIPA, Sistema de Informação para o Património Arquitectónico. Forte de Sacavém, SIPA/DGPC, 2001, (accessed 9 January 2018)

[13] Património Cultural, Direcção-Geral do Património Cultural, (accessed 9 January 2018)

[14] J. A. F. de Almeida (coord.), Tesouros artísticos de Portugal, Selecções do Reader’s Digest, Lisboa, 1982, 668p.

[15] L. M. C. Rosas, Monumentos pátrios. A arquitectura religiosa medieval – património e restauro (1835-1928). s.n., Porto, 1995.

[16] C. V. de Sousa, As intervenções da DGEMN no acervo de pintura mural nacional (1929-72), in: Actas do II Congresso Internacional de História da Arte 2001. Livraria Almedina, 2004, pp. 23–48

[17] A. Cravo, A cal, Caderno Terras Quentes, 2006, pp. 1–5





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