El pasado mes de octubre el Museo Nacional de Beirut, el museo arqueológico más importante del Líbano, reabrió la planta del subsuelo tras un complejo proyecto de restauración y  conservación. La apertura de este espacio, dedicado al arte funerario, amplía de forma notable el área expositiva, que ahora era de dos plantas. Bajo la dirección del conservador Giorgio Capriotti y del arquitecto Antonio Giammarusti, que ha diseñado los amplios espacios en los que se exhiben las obras, estas nuevas dependencias albergan, entre otros magníficos ejemplos, los famosos frescos de la tumba de Tiro. Mediterráneo Antiguo ha querido acercarse a este proyecto -financiado por el Ministerio de Asuntos Exteriores de Italia, a través del departamento de Cooperación al Desarrollo, bajo la dirección de la Dirección General de Antigüedades del Líbano– de la mano de Giorgio Capriotti, uno de sus protagonistas, conservador especialista en pintura al fresco con una larga trayectoria profesional, que ha atendido amablemente nuestra llamada.

Question – Please, could you describe briefly the frescoes in the Tomb of Tyre? 

Answer – Above the arch of entrance appears the goddess Psyche, with butterfly wings, representing the human soul. The walls of the rectangular chamber are decorated with frescoes mural paintings. Two musician mermaids are painted on either side of the counter façade. These enchanting sirens also represent celestial birds intended to guide, with their music, the soul of the deceased to the world beyond. On the lower parts of the walls, there are tromphe l’oeil architectural composition imitating columns, capitals and double wings doors, following to the Pompeian Second Style. The interior scenes are inspired by the fabulous world of Greek mythology. Two compositions appear on the northern wall “Tantalus in the infernal garden” and “Alcestis and Heracles”, while two others are depicted on the southern one: “The return of Hector’s body” and «Heracles and Cerberus”. A unique theme, “The abduction of Proserpina” is divided into two sequences painted on the western wall facing the entrance. All the scenes are separated by standing figures of winged Eros, flanked with rich garlands.

El Museo Nacional de Beirut amplía su oferta cultural con una nueva sala dedicada al arte funerario en la que destacan los frescos de la tumba de Tiro

Question – What can we say about its artistic value?

Answer – What makes the tomb of Tyr unique are the painted frescoes inspired by the Greek mythical themes and expressed with the classical roman language, moreover including some local influences due to oriental inspiration. The figurative contest was created and elaborated in the 2nd cent. AD in Tyr and is the result of an erudite milieu acknowledging a deep spirituality.

Question – Could you describe the previous intervention, the study of the support structure?

Answer – The wall paintings of the tomb of Tyr were detached from the original site in the late 30’s and reassembled in the early 40’s in the lower level of the Beirut National Museum by the English architect Henry Pearson, already active in Doura Europos’ Synagogue (Syria) few years before. The aim of that project was to display the recreation of the original hypogeum.

The area of the basement on which the tomb was reconstructed is a rectangular space, outlined by four concrete pillars, about 30 cm in diameter. The support structure consist of a cage in reinforced concrete, formed by a sequence of 26 vertical rigid ribs (section cm.15 – height cm.320) along the outside perimeter which starting from a platform at floor level, is anchored to the ceiling and the four concrete pillars of the basement. A series of horizontal concrete ribs of the same strength put a belt round the entire rectangular perimeter. The choice of concrete for this structure is justified by both its mechanical resistance and facility with which it can be shaped during the casting phase. As a matter of, the ribs follows the curved surface of the painting, reproducing faithfully the original irregular configuration of the rock support in the tomb, which as it is documented by old photographs taken before the detachment, were not well squared and showed the characteristic features of a directly carved calcareous rock (slight tapering of the walls towards the ceiling, rounding of corners, ellipsoidal surfaces twisting).

Las pinturas de la tumba de Tiro se trasladaron desde su emplazamiento original en los años 30 y se montaron en el subsuelo del Museo Nacional de Beirut en los 40.

It is likely that the system used for the reconstruction of the chamber, reproduced almost faithfully with regard to vertical sections and floor plan, was based rather on a precise architectural survey of the irregular shape of the walls than on the use of complex moulds. It appears that the design for the rib structure, forming a cage, and the building of the supporting walls, which are fixed on it, was made on the basis of a very accurate measured drawing of the hypogeum. The junction on the corners match so perfectly that even at a macroscopic level no reductions or losses can be noted, which might have occurred as a result of the detachment. The only exception is in the entrance (low left corner), where the discontinuity of a red strip shows an evident mistake occurred during the reassembling phase.

The construction of the walls, erected against the rib structure and tied to it, was made from the bottom to the top by means of direct manual shaping with plaster of Paris (semi-hydrated calcium sulphate) mixed with fine stone dust and chemical additives (barium) to harden the plaster. During the dismantling of the gypsum fillings it was possible to examine the in-depth stratigraphy of the support. A flexible lattice work in wood was used as an internal, reinforcing element and guide. The direct shaping of the walls modeled with the intention of reproducing faithfully the curved state of the surfaces was thus regulated by a flexible internal grid, which is anchored to the concrete ribs by means of ties composed of cord. However, the hundreds of tie bridges, rather than a structural role provide regular reference points for the definition of the irregular contours of the wooden lattice work used for the construction of the wall. These reference points were defined by measuring the length of the various ropes in tension. Once the precision of the various lengths on one horizontal level was verified, the rope segments were made rigid by impregnating them with plaster of Paris, supplying an exact reference for the final modeling of the walls which never exceed the 10 cm. of thickness. Except for the right hand wall, all the back of the structure, including these rigid cords are coated with a layer of bitumen, aiming at the protection/water-proofing of the gypsum .

After the completion of the reconstruction of the wall with its rectangular perimeter, it became a statically autonomous system. The stability of which is insured by the cross-bonding of the concrete ribbing. The re-mounting of the paintings, detached in 36 squared panels (max 1 sq.meter each) and reduced to a small thickness from the back (1 cm. ca.), was carried out by direct bedding . During the dismantling of the previous gap fillings has been noticed the presence of beeswax, probably applied for the backing of the panels to avoid risks from moisture, and confirmed by analysis led by Iccrom in 1997. Numerous differences in level, visible under raking light, indicate that the alignment of the rectilinear joints created difficulties. These joints between two sections are contiguous, without substantial loss of material, but the alignment is not always correct resulting in differences in level, which were compensated by pointing.

For the extremely fragmentary areas in between the locula, separated panels were made on which the few remains of a geometric decoration were applied, following the graphic record.  The treatment of the large lacuna, which already existed at the moment of the discovery , were presented by means of a plaster reintegration made of gypsum and filling the lacuna to the level of the original surface. Moreover, large portions of the missing painting, like in the right part of the front wall (Rape of Proserpine) were invented, by suggesting the shapes of missed figures (Athena and Artemis) and the sequence of the painted architecture at the dado with color glazes, using slightly lighter hues than the original. In some places, the original was over-painted to emphasize figurative details. The votive bench along the walls, built with modern masonry materials according to the site record, rests directly on the ground. It is not structurally connected to the concrete ribbing and is not acting as a foundation for the walls. Panels of plaster of Paris reinforced with wood latticework were used for the small entrance, imitating the surface of the carved calcareous bedrock.

Question – Could you talk us about the state of conservation before the restoration project?

Answer – Water rising from the underground occurring accidentally during civil war years, while the museum remained closed, caused alarm for the statics of the structure and large degradation to the surfaces. In such stressful conditions (RH 100% – T 30°) the structure projected by Person in the ’40 performed anyway quite efficiently. Despite the general environmental decay occurred in the whole basement of the museum, the system has guaranteed a substantial static capacity as confirmed by the two assessment missions held by Iccrom in 1997-98, focused on the rescue of the structure. In 1997 the microclimatic conditions of the entire basement, including the area where the tomb was reconstructed were prohibitive and totally incompatible with the conservation of the painting. Persisting conditions of a relative humidity close to saturation in the space enclosed by masonry wall and with the entrance sealed until April 1997, was the main source of decay of the painted surfaces.

La humedad del subsuelo del Museo Nacional había puesto en serio peligro a las pinturas, por lo que la intervención era delicada

This involved mainly two aspects:
1) Biodeteriogenic decay
2) Chemical-physical decay

1.Biodeteriogenic decay: the unfavorable environmental conditions inside the enclosed room of the tomb led to an exceptionally extended and severe growth of heterotrophic microorganisms (e.g. fungi, streptomyces). Abundant quantities of substrata are provided by organic adhesives used for the detachment and never completely removed and by the fixative applied in the larger reintegrated lacuna. Laboratory analysis also revealed the presence of sulfides , probably produces from sulphates (gypsum) migrated to the surface by sulfur-reducing bacteria. A direct effect of the biodeterioration of organic matter was the decay of the wooden structure of the ceiling followed its collapse.

On the painted surfaces, products of the metabolic activity has caused the formation of extended, powdery and variously colored stains (brown on residues of fixative and whitish on adhesives used for the detachment). The action of biodeteriogens, in addition to the detrimental effect on the legibility, has also contributed to the loss of cohesion of some pigments.

2) Chemical-physical decay: a major source for the migration of pollutants towards the surface is the gypsum support. The high water content in the room has started a process of solubilization, migration and recrystalization of soluble salts (sulphates). The capillarity rise from the ground was absorbed by the votive bench and by the panels in between the loculi, leading to a total impregnation of the constituent materials up to a level of about one meter. Here the re-crystallization of soluble salts was particularly destructive , with the plaster edges of the fragments completely invaded by efflorescence, lack of adhesion and advanced loss of cohesion. The thickness of this fragments is generally less than of the paintings above. This, together with the fact that they were applied on the panels in direct contact with the gypsum, might have contributed to the stronger effect of salt decay. Also the salt efflorescence on the higher part of the walls appeared to be made up almost exclusively of calcium sulphate. They were concentrated mainly in the areas close to gypsum fills, forming macroscopic crystals, which however were much less invasive than in the lower part.

Restricted areas of the back wall and the right hand wall show lack of adhesion of the original plaster from the gypsum support. Also in this part the destructive thrust of sulphates appears to be directly proportional to the thickness of the original fragment.

During the cleaning, after having removed sedimentation, biological growth and soluble salts which were hiding the paintings, it was possible to identify calcareous incrustations and incrusted soil which were never removed completely during the previous intervention of the ’40. Moreover, considerable quantities of organic adhesives, used for the facing during the detachment, have been found in the roughness of the plaster.

Question – Explain us, please, what kind of conservation works do you have develope.

Answer – The restoration project, executed in six months during the year 2010, has been focused in two main issues: preventive and conservative. Preventive: achieving the reestablishment of a correct stability of temperature and relative humidity in the environment of the tomb (T 20°-25° / RH 55-65 % ). Conservative: facing the complete treatment of the wall paintings, including consolidation of the structure, fixing of renderings and paint layers, cleaning of the surfaces from microbiological growths and salts, removal of previous interventions, new esthetical presentation.

El proyecto de restauración de las pinturas, que duró seis meses en el año 2010, tuvo un doble enfoque: preventivo y de conservación. 

On the basis of the positive evaluation of the stability of the support structure and recognizing the high level of fidelity achieved in the reconstruction of the tomb using Pearson’s survey, it was decided not to replace the supports and to maintain the structure as an historical witness of the conservative approach of the Near East archeology in the first half of XX cent. Having excluded the possibility of transferring the paintings , which would have been traumatic for the already weary painted surfaces, thoughts turned towards problems related to the preservation of the system.

The strategy was directed as first to prop and reinforce the structure where necessary, and than to achieve the whole de-humidification and water proofing of the basement, in order to establish a compatible microclimate, suitable for the conservation of detached mural painting.

The different phases of interventions were articulated as follows:

– checking and removal of the protective structure and temporary facing on the right wall. Reinforcement of the stability applying new series of steel tension wires through the plaster wall-panel to the concrete structure behind;

– removal of microbiological growth and application of poultices soaked with a suitable broad-spectrum biocide (Solution of Water-Ammonia-Proctol-Alcool 1:1:1:1) , through sheets paper by brush;

– re-establishment of cohesion and adhesion of the paint layer, by infiltration of microacrlylic resins in idroalcoolic solution ( Acrylmat ) and acrylic resin in emulsion (AC33);

– mechanical removal of salt efflorescence and partial extraction through basic poultices: 1 lt. water + carboxymetylcellulose + cellulose pulp + 50 gr. sodium bicarbonate + 30 gr. ammonium bicarbonate);

– removal of residues of calcareous incrustations by mechanical action (scalpel, micro-drill, fibre glass pens, wishab rubber sponge);

– removal of last insoluble salt veils by Amberlite exchange resin (hard cationic OH)

– removal of old residua from organic glue (protein) used in the detachment of the’40 by solution of formic acid and distilled water 1:1 and subsequent neutralization by solution of ammonia and water 1:1;

– adsorption of dark stains by poultice of sepiolite and distilled water; – final cleaning by dimetylsulfoxyde, by brush;

– partial detachment and correct re-alignments of differences in level along the joints between separately detached sections;

– recording (scale 1:1) of the pictorial reintegration of figurative details from the previous interventions of ’40;

– mechanical removal of the gypsum fills in the deep lacuna, protecting the edges of the surfaces by previously facing them with gauze and acrylic resin in solution (Paraloid B72 in acetone 20%);

– fillings of the lacuna, using a plaster with similar characteristics to the original in terms of mineralogical compositions, granulometry, colour and morphology.

According to the type of lacuna the plaster has be applied in three different levels:

a) flush with the original surface for the reconstructible levels; mortar composed by white hydraulic lime, fine marble powder , fine calcareous powder, 1:1:1 ;

b) at the level of the abraded original plaster in worn areas ; mortar composed by brown hydraulic lime, fine marble powder, medium calcareous powder, 1:1:1 ;

c) slightly below the level of the original surface for not reconstructible lacuna; mortar composed by brown hydraulic lime, medium white calcareous powder, medium black calcareous powder, medium yellow calcareous powder 1:2:0,5;0,5. -the esthetical presentation of lacuna has been based on:

a) tone lowering of superficial abrasions of the paint layer by using neutral water colour glazes,

b) reintegration in “tratteggio” of the reconstructible lacuna already filled flush to the originals surface.

The theoretic principles of this esthetical presentation was not to hide the passage of time over the surfaces, including its decay, or to deny gaps and abrasions that occurred in the past. Even the interruption of text (lacuna), indeed has to be achieved as part of the history of the monument and linked with the value of its authenticity.

The case of the tomb of Tyr, emblematic for the presence of such extensive system of losses, reveals how the reading of ancient paintings involves an issue of visual perception, in other words a question of close relationship between gaps and original areas, even if severely fragmented.

According to this, the intervention focused rather on the search of a new balance between original and lacuna, avoiding any trial of vast reconstruction, fake imitation or didactic hypothesis, but achieving at the same a satisfactory level of readability.

Author

Mario Agudo Villanueva