Update on state of conservation

edited by Elisabetta Giorgi


The 'work-site card system' (cf. the article Graphic documentation for the restoration project by the same author) has been organized by selecting 5 categories of objects, each identified with their own code: the archaeological pieces (RA001-n), the pilasters (P01-10), the coupled columns (CB01-48), the slabs (L01-69), and the decorated undersides of the arches (SA01-58). Individual elements or rather those that cannot easily be grouped together, such as the cantharus, the cosmatesque cornice, the pavements and the plaster surfaces of the walls have all been subject to study. In order to avoid restrictions as a result of organizing the data a priori, the database, which will make it possible to systematically structure the diverse queries that arise, was established only after the compilation of the cards.

The archaelogical pieces

The 'work-site card system' was organized in such a way as to contain the principal data relating to the identification of the piece in question, to its formal and historical characteristics and to its state of conservation. Specific entries were dedicated to the characteristics of the mural support; for this reason it was considered important to include a heading that referred to the 'surround' of the piece, in other words, the surrounding wall area whose careful examination may lead to useful information concerning the history of the piece itself (fig. 1). Quite often this area has revealed the superimposition of different layers of intonaco and traces of previous fixtures. The direct analysis of the surround, collated with historical and iconographical data and in some cases supported by laboratory tests, has helped to reconstruct the museological history of the individual pieces, which represents one of the elements to be taken into consideration in the final phase of the project: many pieces have in fact been added or moved since Muñoz's arrangement without taking account of the historical and typological criteria that he had adopted.

The comprehensive evaluation of data on the conservation of the pieces is fundamental to the project. It has emerged that residues from various types of mortar can be found on 90% of them (fig. 2). In the majority of cases they are traces left from the former re-use of the piece: one must recall that many pieces found by Muñoz had been turned upside down and re-used in the pavement of the basilica. In other cases, instead, the mortar has been used as a kind of daub and may therefore have been put there for aesthetic reasons, though this will be a subject for further study.

Another cause of deterioration on many of the pieces derives from the iron brackets with which they are fixed to the wall. Apart from evident patches of ferrous oxide and their relative drip paths, they have also inflicted damage of a mechanical nature. Where they have been inserted, former cracks have become larger, or new ones are evident. The majority of the pieces will have to be removed, cleaned and put back in place and in this case the most seriously damaged or those that however might interfere with the conservation of the piece itself, will have to be replaced with others in stainless steel. Only in a few cases have phenomena of disintegration of the marble been noted. For these it will be necessary to carry out preliminary consolidation with ethyl silicate, a product used above all for silicate materials that has proved effective also for calcareous ones. In particular, the larger-sized pieces have been coarsely repaired with cement plaster that poses not only conservation problems (mechanical stresses, presence of salts etc.) but also aesthetic ones. Also in these cases, specific treatment will be required in order to remove the cement and substitute it with a specially prepared hydraulic lime.


The coupled order: columns, bases and capitals

A comparative study of the 'work-site' cards relating to the coupled columns has revealed significant data on the historical and figurative background of the columns themselves (see article by Laura Morgante), on static and structural problems and those concerning the conservation of the surface (fig. 3-4). The most important piece of data to emerge relating to all the columns is the presence of a film presumably applied during Muñoz's restoration work. This film most likely served a dual purpose: firstly to protect the marble surfaces already in a state of deterioration and secondly to tone down the apparent difference between the original columns and the new ones added during restoration. From the point of view of color, the former produce a different chromatic effect not only due to the patina of time but also to the grayer marble used for the replacements. Over time the film has been subject to considerable and varied forms of deterioration that have resulted in serious decay phenomena. In places it has become detached, taking part of the marble support surface with it. In these cases, white 'blotches', which indicate none other than the emergence of the constituent material, can be noted. Another grave phenomenon that has been observed is the formation of black crusts evident in those areas subject to rainwater washing. This problem, which is getting worse and worse as a result of widespread environmental pollution, produces not only aesthetic damage but actually eats into the stone material with consequent losses of the latter. It is interesting to note that this type of decay exists on both the original coupled columns as well as on the substituted ones. The phenomenon indicates that the worsening level of pollution has led to a totally irrational mixture between old and new, which at this stage can only be identified through careful analysis. Other phenomena are less apparent, such as disintegration, rainwater washing and the presence of cement. In certain cases the latter has been hurriedly applied, concealing and distorting the original shapes such as the moldings on the bases and capitals. And finally the presence of serious flaking at the joints between shaft and base (fig. 5) and between shaft and capital must be noted.

The slabs

There are 69 slabs that act as supports for the pilasters and coupled orders. The identification of an individual slab is determined by recognizing its perimeter, even though this is not always clear because of the numerous repairs carried out with different materials, such as brick, marble fragments and mortar reintegration of various kinds. The card system other than providing dimensions and historical data (re-used material, inscriptions and incisions both before and after construction, traces of color, etc.), also focuses on conservation problems. The presence of thick surface deposits, the accumulation of wax, dust and improper applications of cement mortar, have resulted in the formation of a not easily removable layer on a considerable number of elements. Cement mortar used to fill in the joints between the slabs and to make repairs has further aggravated the conservation problem. It is useful to note that the slabs fulfil the function of inhibiting rising damp from the underlying soil. In a sense they act as a filter of the salts that dissolve in water. There are high levels of nitrates, whose hygroscopicity could in part explain the film of water that, at certain times of the day and under particular climatic conditions, can be found on the surface. Where the slabs are continuous, phenomena of surface decay, such as disintegration, concretions and black crusts, are more evident

The decorated undersides of the arches

There are 58 undersides decorated with geometrical motifs with a prevalence in white and gray triangles on the shorter north and south sides and red and green drops on a white background on the longer east and west sides. The intonaco of the intrados and undersides with their decoration all pertain to the 1914-16 restoration work, with the exception of two small original fragments. One of the two fragments can be found on the north side (SA10, fig. 6), and has the following characteristics:

Type of decoration:

- geometrical motif with white and gray triangles.

Production technique and constituent materials:

- incisions carried out on wet intonaco;
- a frescoed gray background with the subsequent addition of white triangles.

State of conservation:

- there is lack of adhesion between the intonaco and mural support in the central area;
- the surfaces indicate abrasions and widespread patches of whitening.

The other original fragment can be found on the east side (SA56, fig. 7):

Type of decoration:

- motif with red and gray-green drops.

Production technique and constituent materials:

- preparatory design carried out with a gray or red line on wet intonaco;
- a frescoed white background with the subsequent addition of drops.

State of conservation:

- there is lack of adhesion between the intonaco and mural support in a limited area;
- the only lacuna present has been patched up with coarse plastering;
- the surfaces indicate widespread abrasions.

The decoration of all the other undersides carried out during the 1914-16 restoration work was performed in two different ways that have characteristics in common and can be summarized as follows:

Production technique and constituent materials:

The intonaco surfaces were most probably painted a secco or when the carbonation process was almost complete. As a first step, a preliminary layer of white lime-wash was applied, on which the incisions to guide the decoration were made by scratching the dry intonaco with a pointed instrument; at times the intonaco may not have been completely dry. In the latter case, the design was traced with pencil lines. In any one arch, both incisions and pencil tracing may be present. Subsequently the gray triangles or the red and green drops were added. In many points the color is visible inside the furrow of the incision. On the undersides decorated with the drop motif it is often the case that the added color does not strictly follow the incision guidelines. In order to diminish the effect of a 'modern' reconstruction, during the final phase of the project, the intrados surfaces were aged by marking and scratching the intonaco and then coating it in a brown color, applied with a sponge or a brush and then partly removed with abrasive action, clear signs of which still remain. The internal and external arched lintels have a yellow ochre color pertaining to the final coloring of the vaults and the external wall.

State of conservation:

All things considered, the state of conservation is good. The presence of some cracks and fractures does not indicate any specific problems of a static nature, except perhaps the underside of the arch in the east corridor. Also with regard to the lack of adhesion of the intonaco there are no really serious detachments to draw attention to. The lacunae of the intonaco, mainly evident in the external arched lintel of the undersides, are small and infrequent. Lack of adhesion and cohesion in the paint layer is rare.

The intonaco

The majority of the intonaco surfaces appear to have maintained the configuration given them by Antonio Muñoz in 1914-16, whose restoration also involved some repairs to the final plaster layer due to adjustments during the project. The archaeological pieces were often fixed with gypsum-based mortar, applied to a traditional wall structure with lime mortar and pozzolana, and this has led to incoherence from a physical and chemical point of view and to the accumulation of harmful salts throughout the entire structure. Despite this, the phenomena of deterioration are not evenly distributed over all the surfaces. On the internal sides of the corridors there are generally widespread surface deposits and black crusts, detachments, and losses of intonaco and color. The presence of nails and iron clamps used to attach the majority of the archaeological pieces to the walls has caused appreciable damage to the wall structures, the intonaco and the pieces themselves. In particular, it must be noted that the south and east walls are the most damaged. The former,up to a height of 1.50 m from the ground, has deep lacunae, losses of intonaco and color, and patches of cement. Rising damp has reached its maximum levels, exceeding the impost of the vault; in the three niches for lighting there are serious losses of rendering, intonaco and disintegration of the constituent wall materials (fig. 8). The south half of the east wall has in recent years been stripped of its intonaco, without however considering the aesthetic result. Many deep channels and repairs to the wall structure with cement mortar are visible, and these have seriously damaged the 11th century brick curtain-wall. At the north end of the same wall a portion of 18th century fresco, whose paint layer shows clear evidence of deterioration and loss of color, is visible. The intonaco of the bases of the coupled columns is seriously affected by rising damp with cracks and detachments on the top parts; there are numerous repairs on the wall above the small arches. The intonaco of the vaults precedes Muñoz's restoration work and, on the whole, is well conserved. Cracking is evident in certain points due to static problems. Only on the east side have there been losses of the paint layer, as a result of its lack of adhesion to the support, which is here covered by a thick deposit of soot particles. Where the intonaco has been replaced due to the installation of electric circuits, there is a change in color. Similar phenomena are evident on the external surfaces, as well as a loss of color due to rainwater washing.

The cantarhus

The fountain that stands in the center of the cloister was constructed in 1914 using the parts of an ancient cantharus that Muñoz found in the monastery gardens. These parts are made up of two marble cups one above the other, the lower one adorned with leonine heads and mascarons. Decay phenomena are largely due to the presence of water and to restoration work carried out with improper materials, such as extensive areas of cement plastering and bronze or iron brackets (fig. 9). The water is responsible for the thick calcareous deposits, whose removal will require particular caution in that they have become firmly embedded in the marble surface that had formerly been subject to serious disintegration and fractures. Moreover the presence of water has generated severe biological aggression in the form of lichens and algae, which have further jeopardized the aesthetic effect of the sculptural forms. The damage caused by the brackets is largely of a mechanical nature: the changes in temperature that affect the brackets and their insertion into the cement mortar have resulted in diverse stresses and produced cracking and fractures.

The cosmatesque cornice

The state of conservation of the cornice has been mainly jeopardized by air polluting agents, particularly temperature variations and rain. The tiles that alternate with the marble slabs which together constitute the most characteristic elements of the cornice, have been made with polychrome marble inlay (porphyry, rosso antico, green serpentine or Sparta stone, white fine-grained marble). These tiles do not appear to have serious detachment problems except where the temperature range is higher. In certain cases rainwater washing has evenly distributed both salts and dirt, creating a veil of whitening that conceals the color of the marbles themselves. In the less exposed areas heavy surface deposits, sometimes in the form of actual concretions, are evenly distributed on the brick and stone elements. Lacunae resulting from the loss of tiles and serrated edges have allowed the upper portions to slip down. Some of these lacunae derive from the mechanical action of tall vegetation present in the cloister.







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Fig. 1 - Detail of a residual 'surround' due to a new arrangement.


Fig. 2 - Deterioration on piece no. 187; deposits of mortar and fractures can be noted. (an analysis of its dimensions led to the discovery that this was the piece that, turned the other way round, had left the surround visible in Fig. 1).


Fig. 3 - Part of the data card on the state of conservation of the coupled columns.


Fig. 4 - Legend for mapping the state of conservation of the coupled columns.


Fig. 5 - Detail of loss or serious flaking at the base of a coupled column.


Fig. 6 - Detail of the decoration of the underside of the arch SA10.


Fig. 7 - Particolare della decorazione del sottarco SA56.


Fig. 8 - Detail of the decoration of the underside of the arch SA56.


Fig. 9 - The cantharus; the metal brackets and the cement plaster can be noted.