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- INTRODUCTION -

Before describing the techniques used to conserve the mosaics moved from Zeugma, a short premise is necessary. A mosaic removed from site is an artifact that has undergone an irreversible operation: it has been separated from its original context (site or monument) and stripped of some of its original parts (original preparatory layers); much evidence left by time has been cancelled, together with its relationship to the architectural setting to which it belonged (irregularities in the levels, historic traces).

Guidelines

Given these premises, and taking into account the radical transformation from architectural-archaeological element into an object stripped of its antiquity in order to assume a new nature, the conservation-restoration professional has to plan the recovery treatment. The artifact’s physical state has changed and hence the guidelines to follow for the conservation treatment have to reflect this change.

The reference points to bear in mind are:• Conservation of the historical and technical data

contained;• Chemical and physical compatibility of the

materials used during conservation in order to re-create a setting bed for the tessellatum;

• Total reversibility of materials used during the treatments;

• Logistic concerns of handling, moving and storing the mosaic in a safe and practical way;

• Final presentation, in order to enable viewers to appreciate the surfaces as close as possible to their true essence.

These were the principal constraints that governed the project. The following procedures were adopted in order to provide adequate solutions to those constraints.

Procedures Any historical information still extant was preserved through documentation: all data that would have been lost through the operations of removal from site and restoration, or data that had been lost, were tracked and

archived through all the forms of documentation available . We respected the criteria of material compatibility between ancient and new materials employed during restoration by applying the tesselatum on a setting bed of cocciopesto similar to the mosaics’ original support on site. In reconstructing a layer of lime-based mortar, we reproduced the conditions of chemical and physical interaction between the mosaic and new materials that are similar to the original ones. This approach assures long-term durability with full respect for the ancient materials and meets the objective of ensuring complete reversibility of the treatments; at the same time, it reproduces a visual effect equivalent to the original one. We resolved the logistic concerns by putting the mosaics on supports that are light, rigid and stable, following the outline of the geometric and figurative design of the mosaics themselves. They are divided into smaller sections so that they can be easily handled without risk of damage. The relatively low weight of the individual sections will facilitate all operations of storage, transport, assemblage for display and dismantling for maintenance operations. Finally, we believe that we have met the needs of presentation by adopting mimetic cutting lines that follow the design outlines of the composition. Once the various sections are put together, this solution restores visual unity, which is indispensable for proper appreciation of the mosaic surfaces. Yet, the key element that has marked the restoration treatment of the Zeugma mosaics is the complete reversibility of the materials and techniques used and the absolute transparency of the operations carried out, thanks to documentation and to diffusion of information on the project.

Before describing the operations implemented during conservation, we must stress that we found the mosaics in a variety of extreme conditions, regarding both their detachment and conservation. In order to better understand the various steps in the conservation process, it is worth looking at the expected final result of the treatment, which is to have the mosaic applied on light-weight panels, about 1 m2 each, cut following the compositional outlines of the original mosaic design. The single panels are easy to move and store. When reassembled, they restore the complete image of the mosaic floor. The panels are made of a sandwich structure of aluminum honeycomb between two layers of fiberglass-reinforced epoxy resin, and are prepared with a lime and

• Chapter two •

The Conservation Intervention

William Aylward

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brick-powder mortar (cocciopesto), which functions as a new setting bed for the tesserae.

The sequence of the operations can be summarized as follows:

• Verification of the adherence of the tesserae to the temporary support, which is the canvas covering applied during removal from site and, where necessary, putting the tessellatum on a clay table in order to produce a new temporary support in place of the decayed canvas for implementing the emergency operations, including the application of new cotton gauze;

• Documentation;• Removal of the reinforced concrete applied after

lifting before our arrival and of the decayed original preparatory layers;

• Application of individual sections onto lightweight sandwich panels;

• Removal of the canvas or cotton gauze covering• Integration (using tesserae) of sporadic new

lacunae and mending old ones with lime mortar;• Surface cleaning;• Consolidation of the mortar filling between the

tesserae;• Surface protection.

- PROCEDURE -

Verification of the adherence of the tesserae to the temporary support and transfer onto clay

The first operation is to verify the adherence of the canvas covering applied when the mosaic was removed from site before our arrival: where the canvas is decayed, or where a significant loss of tesserae occurred during detachment, or where new cuts are required, the tessellatum is temporarily put on a clay table in order to integrate the lacunae, apply new cotton gauze and make any new cuttings required.

The clay is applied on the reverse side of the tessellatum, which is later turned over, in order to proceed with the removal of the canvas applied to the front for lifting from site. While this technique is rather time-consuming, it permits us to check the condition of the tessellatum and, if necessary, do some preliminary restoration (figure 1). In the case of mosaics detached in sections that are larger than one square meter or with cuts that interfere with the aesthetic of the mosaic, a new general plan for the sections is drawn and the pavement is subdivided into pieces of a good size for reapplication. The cutting lines are designed to follow the borders of the figures and geometric patterns, to respect the original mosaic scheme and to permit a better reading of the reconstruction.

A new double layer of cotton gauze is applied with wheat-flour paste to complete this phase (figure 2).

Removal of the reinforced concrete supports and decayed original preparatory layers

All the layers of reinforced concrete that were applied before our arrival immediately after the lifting from site have to be removed. The same treatment is given to the remaining original mortar if it is cracked or crumbling. When the pieces of mosaics are safely supported by the canvas, the sections are turned over and the reverse side of the tessellatum is cleaned. The objective of this operation is to create a levelled, stable surface, ready to receive the mortar of the new setting-bed layer (figure 3). In all cases where the solidity of the original materials permits, we keep the setting bed of the tesserae.This operation is carried out by hand, using electrical cutters with diamond disks, pneumatic tools and chisels.The final passage in the cleaning of the reverse sides is sand-blasting at 4 atmospheres using fine abrasive materials.

Application of individual sections onto lightweight sandwich panels

The methods of application of the mosaic to the panel are of two types, depending on whether the original application layer was previously removed: application from the front (which means the sandwich panel is prepared on the floor and the tesselatum is applied face up) or from the reverse side (which means that the tesselatum is face down and the sandwich panel is applied on top of it). Due to the heavily compromised state of the original mortar, the method used in the majority of cases was application from the front. Let us see the technical operations performed to reapply the detached sections to the lightweight sandwich panels:

Figure 1. Mending of the small lacunae with tesserae

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Figure 2: Application of new canvas

Figure 3. Cleaning of the reverse side of the tesserae with pneumatic tools

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Figure 5. Cutting of the panels along the traced outlines with a jig saw

Preparation of the lightweight panel outlining the dimensions of the single sections

Once all the sections are cleaned and ready for application, they are assembled temporarily face down on a single panel the size of the entire mosaic. The overall panel is assembled using epoxy resin and fibreglass bolts joining a sufficient number of standard lightweight panels (measuring 146 x 300 cm). The thickness of the panels used depends on the thickness of the tesserae of the mosaic being processed. Normally, lightweight panels, 24 mm thick, are used. On this single panel are traced the outlines of the different sections, the section number and all references needed for the application. The panel is then divided by cutting along the traced outlines with a jig saw; (figures 4 & 5).

Preparation of the adherence layer for the mortar with gravel and epoxy resin

Once cut, the lightweight panels receive a layer that will guarantee adherence between the panel and the lime-based mortar of the new setting bed for the tesserae. The adherence layer is made of gravel of volcanic mineral earth (pozzolana) glued to the panels with epoxy resin. Fig. 11The gravel of volcanic origin was chosen over traditional stone gravel for a question of overall weight. An experiment carried out using three different gravel types – stone gravel, expanded clay (LEKA) with small granulometry and volcanic mineral earth – led to the following results: 30% difference in weight between the stone gravel and the other two materials used. The volcanic gravel was ultimately chosen because it combined the advantages of minor weight with being easily obtained (as it is of local extraction), together with an excellent adherence function. Analysis of possible soluble salts was negative, confirming the suitability of the material.

Application from the front of sections on lime-based mortar

The prepared panels are ready for application. After planning of the succession of individual panels to apply, the application starts with the central panel of the mosaic positioned according to its collocation in the mosaic on a wooden working table stretched over the floor. The direct contact with the floor limits vibrations during the beating and other work phases. The lightweight panel is framed with strips of wood and metal fixed to the underlying timber panel layer. The framing strips are of the same height for the complete mosaic, based on the height of the lightweight panel, the depth of the tesserae and of the mortar necessary. The depth varies from mosaic to mosaic from a minimum of 2.5 to a maximum of 5 cm. At this point an hydraulic mortar is applied. 1The mortar is spread with the utmost care to compress and thoroughly work the material with spatula and trowels in order to obtain a very compact layer, neatly applied to the lightweight panel and with no air pockets or bubbles.

Mounting the sections on the panels

The sections, placed face down, are slightly wetted and then covered with a liquid mortar (buiacca)2 which penetrates the spaces between the tesserae and acts to connect the tesselatum and the new setting bed; Thus prepared, the section is positioned on a compressed wood-fibre panel, turned front side up and then placed on the new setting bed. At this point, the section is pushed into the lime-based mortar with the help of modified heavy finishing trowels. This operation is repeated until the tesselatum is perfectly aligned with the timber and iron elements of the frame prepared for the mounting. Once the first section is completely mounted, the process continues

Figure 4. Planning of the mosaic reassembling

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with the next ones, at a rate of some two or three sections a day. Once all the sections are mounted, the mosaic is left untouched for about a month, giving the mortar the time to set up and harden. In the case of floors where the original mortar of the setting bed was in solid conditions and therefore it has been decided to leave it, part of the mounting process is carried out from the reverse side according to the following procedure: Levelling: the original setting bed of the mosaic, with its front covered with canvas/cotton gauze and face down, is levelled in order to obtain a even mortar layer of continuous depth. If this is not possible through levelling the original mortar layer, an even level is obtained by applying a mortar similar to the one used for the new setting bed, levelling out the reverse side to a uniform depth (figure 6).

Consolidation

Before the lightweight panel is applied, the original mortar and any new mortar used to level out the reverse side, is consolidated using an acrylic resin emulsion (Primal AC3315% in water) until saturation.

Application of the lightweight panel

Once the consolidation has been completed and any new mortar has completely dried out and set, the lightweight panel is applied – mosaic still face down – using epoxy resin mixed with sieved sand (figure 7). Once the epoxy resin has set up, the mosaic – complete with its lightweight panel – is turned over again. Now the mounting of any other sections proceeds using the method of application from the front with all the other operations just described. It is important to specify that mounting from the reverse side can only be done on a single section,

no matter whether it is an entire pavement or the central scene of a mosaic. The other sections of the mosaic are then mounted around it, using the method from the front. The method from the front allows an entire pavement to be mounted with a single coherent method, but with the method of mounting from the reverse side, one has to accept one of two possibilities: either the whole floor is mounted in a single piece (with all its inherent problems), or a mixed technique is used, with the central section mounted from the reverse side and all the others mounted from the front.

Removal of the canvas/cotton gauze covering

The removal of the canvas applied for the detachment and of the cotton gauze applied after the integration on clay is executed by the creation of a moisture chamber obtained by pushing hot water vapor under a polyethylene sheet tightly covering the mosaic section. After about one hour, the hot vapor has dissolved the glue to a point where the covering can be gently removed; then follows a patient, mechanical operation to remove any remaining glue from the mosaic surface (figures 8 & 9).

Integration of sporadic lacunae and mending of antique lacunae with mortar

The troubled history of these mosaics during their removal from site, transport to the museum and storage caused a considerable loss of tesserae, many of which were recovered between the various layers of mosaics. These lacunae, normally small but present in great number, were restored after an accurate documentation using the original tesserae recovered and, in some cases, new ones. The lacunae already present at the moment of excavation (identified through the scanty photographic

Figure 7. Application of the new support from the reverse side.

Figure 6. Application of the new support from the reverse side

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Figure 11. Mending of lacunae with mortarFigure 10. Restoration of the tessellatum with tesserae

Figure 8. Removal of the canvas with water vapor Figure 9. Removal of the canvas with water vapor

Figure 13. CleaningFigure 12. Cleaning

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documentation available) were mended with mortar (figures 10 & 11).

- CLEANING -

This operation is carried out using chemical and/or mechanical systems according to the kind of surface deposits present. If there are carbonized surface deposits, cellulose fibre poultices soaked with ammonium carbonate (30 g/l), EDTA (25 g/l) and a detergent (Neodesogen 10 cc/l) are applied. The chemical cleaning is followed by mechanical finishing using various tools: plastic scrub brushes, an electric, modified, low-velocity angular cutter or a drill driven by compressed air, and scalpels. The water used for scrubbing and rinsing the surfaces is immediately removed with an industrial vacuum cleaner, together with the dirt and any chemical substances applied (figures 12 & 13).

RECONSTITUTION OF THE MORTAR - FILLING BETWEEN THE TESSERAE -

In most cases, the original mortar filling between the tesserae had been partially or totally lost during the mosaic’s removal from site or during restoration. In the areas where losses did occur, a new layer of liquid hydraulic mortar is brushed on, and any excess is immediately sponged off (figures 14 & 15).

Surface protection

Once the mortar applied between the tesserae has set up, on the clean surface a protection layer of 1.5% of acrylic resin (Paraloid B72) in acetone is brushed on.

Lifting of five new mosaics from Zeugma, area B

As part of the conservation/maintenance of the fluctuation zone in area B, during the period between October 2000 and October 2003, five new mosaics were discovered at Zeugma, owing to unprecedented lowering of the lake water level in different unexcavated areas during the ZAP 2000 program. The mosaics were in the water fluctuation zone within which conservation in situ is particularly difficult and risky because of wave erosion (figure 16). These mosaics were detached from the site and transferred to the museum for conservation treatment.

The lifting process can be summarized as follows:• Preliminary surface cleaning• Documentation• Consolidation of movable tesserae and edges• Temporary support of the mosaics• Planning for cutting in sections• Cutting• Lifting

Figure 14. Application of liquid hydraulic mortar between the tesserae

Figure 15. Application of liquid hydraulic mortar between the tesserae

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Figure 16. One of the new mosaics discovered at Zeugma in the water fluctuation zone

Preliminary surface cleaning

This operation is carried out to remove all extraneous material from the mosaic surfaces. By using soft plastic brushes, vacuum cleaners and synthetic sponges soaked in a 2% solution of NeoDesogen in water, all dust and debris is cleaned from the tessellatum (figure 17).

Documentation

A complete graphic and photographic documentation is made during the excavation and after the cleaning. This documentation is useful for the later task of re-application of the mosaics on panels. A 1:1 relief is taken on sheets of polyacetate, tracing the principal lines of the figures and the geometric patterns. All the hand drawings combined with photographs are processed with computer assisted design (CAD) software to produce detailed drawings for documentation of the conservation process. All data on the general condition of the mosaic pavements, the areas of lacunae or degradation are traced on graphic maps.

Consolidation of the movable tesserae and edges

Before applying the temporary support on the surface of the tesserae, it is necessary to fix all loose elements so that tesserae are not lost during the lifting operations. For this purpose, infiltrations of an hydraulic lime mortar made

of sifted stone powder and hydraulic lime Lafarge (ratio 1:1) are carried out to consolidate the edges and any loose tesserae detached from the original bedding layer. All the lacunae are accurately cleaned and filled with a lime-based mortar made of sifted stone powder, brick dust and lime (ratio 2:1) (figure 18).

Temporary support of the mosaics

To provide a surface support to the tessellatum and fix the tesserae in their original position, a double layer of cotton gauze glued with PVA is applied on the surfaces. The use of PVA was necessary because of the presence of humidity on the reverse side of the mosaics, due to the rising water of the dam. Any other glues, such as acrylic resins or flour paste, are extremely sensitive to humidity and do not adhere properly to the gauze in a wet environment (figure 19).

Planning for cutting in sections

Before cutting the mosaic’s surface, a general plan of the sections is drawn, taking the decorative patterns and the condition of the mosaics into consideration. All the cutting lines are designed to follow the borders of the figures and geometric patterns, to respect the original mosaic scheme and allow for accurate reconstruction. Planning is also necessary to provide the correct number and size of wooden panels needed for temporary support of the sections for lifting, transportation and storage.

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Figure 17. Preliminary surface cleaning before lifting Figure 18. Consolidation of the movable tesserae

Figure 19. Application of the canvas and cutting the mosaic’s surface in sections

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Cutting

Using the plan, the cutting lines were traced on the upper part of the mosaics and all sections were numbered and documented. The mosaics were cut along these lines with mechanical means and pneumatic tools.

Lifting

The lifting is done by detaching all the preparatory layers (block technique) or only the upper part (nucleus layer). This is accomplished with the help of long metal cutters. All the fragments are placed on the wooden panels, protected by a geotextile sheet and transferred to the camp deposit and laboratory for the conservation process (figures 20 & 21).

Figure 21. Lifting of the mosaicFigure 20. Lifting of the mosaic