The Technique of Plaster Preparation for the Minoan Wall Paintings at Tell el-Dab'a, Egypt - Preliminary Report

The archaeological excavationsat Tell el-Dab'a, Egypt have been carried out over more than 30 years by the Austrian Archaeological Institute in Cairo under the direction of Prof. Dr M. Bietak. In 1989 they produced a major surprise in the form of huge quantities of plaster fragments in area H-I at 'Ezbet Helmi (Fig. 1). The first fragments discovered showed linear architectural decoration, executed in red, blue, ochre, black and white colours. The lines had been laid out by means of cord impressions in the wet plaster. The technique, as well as figural motives such as bull leapers, a half-rosette frieze, griffins and maze patterns, showed immediately that the paintings cannot be identified as Egyptian (Figs. 2-4). More detailed technical and iconographical comparisons showed connections with Aegean paintings, in particular with the famous wall paintings at Knossos and on Thera. As a consequence, it became more and more likely that the paintings from Tell el-Dab'a/'Ezbet Helmi had been produced by Minoan artists (Bietak 1992; 1994).

In recovering archaeological finds, and in particular frescoes, the chemical properties and mechanics of the soil are of decisive importance. It makes a significant difference whether the material to be removed is embedded in loose, sandy, loamy, dry or wet ground, or, as in our case, in Nile silt under perennial irrigation for many decades. In order to restore the wall plaster fragments from 'Ezbet Helmi it was therefore necessary to develop techniques adapted to the specific circumstances (Seeber 1994).

The site, a palace quarter of the early Eighteenth Dynasty, was originally situated on a levee east of the Pelusiac branch of the Nile, which remained above the periodic Nile inundations. In recent centuries, the surface has been considerably levelled and used as agricultural land. Since antiquity, the continuous silting up of the Delta has caused a considerable rise in ground water level. In addition, perennial irrigation with the water wheel, following the construction of barrages during the last century, has caused seasonal saturation of the soil with water. One also has to take into consideration that the salvage work on the frescoes had to be carried out under considerable pressure of time, as irrigation in the surrounding fields often caused flooding of the excavation areas. Therefore the following working steps were followed. The outlines of the plaster fragments, which vary in size from a few square centimetres to half a square metre, were exposed with a variety of spatulae, joint irons and similar tools. They were afterwards removed along with the soil on which they had rested. The often soft condition of the plaster demanded special care in the process of removal, in order to prevent disintegration due to rapid drying under Egyptian climatic conditions.

Excavation and removal of the pieces was often hampered by the fact that most of the pieces were found in compacted dumps, one fragment on top of the other. Some deposits had accumulated to the height of one metre (Fig. 5). Salvage operations were often also complicated by the fact that the painted surfaces lay face to face with the painted surfaces of other fragments. For this reason we had to make alterations to our techniques of lifting and consolidation. Larger fragments could only be separated in the excavation laboratory, but some in situ treatment was nevertheless invariably necessary. First the backs of the plaster fragments had to be consolidated in situ. Then they had to be padded with paper to prevent disintegration during transport (Fig. 6). If the painting faced upwards it was sprayed with distilled water and immediately covered with a protective layer of soft paper handkerchieves or similarily smooth paper in several layers. Tissue with any surface structure should be avoided. On top of this padding a thin layer of plaster was added. Afterwards the pieces were transported to the excavation storerooms.

THE PLASTER

The plaster consists of lime with small additions of quartz sand. The lime was most probably prepared by beating in order to achieve a high degree of compactness. This can be concluded from the lack of air pockets and cracks shown by microscopical examination. Even thick fragments with a width of 12 cm. show this quality. The plaster was applied on thick mud bricks, as the schematic diagrams in Figs. 7-11 show.

Most plaster pieces display a very smooth, almost polished surface. Stucco relief with a painted surface is also present among the finds, and shows the same surface finish. All of the plaster fragments so far examined consist almost exclusively of pure lime, some of them with a very small sand admixture. The thickness of the wall plaster varies from 0.5 cm. to 12 cm.. It was applied in one or several layers on the mudbrick walls. The surface was covered with pointed depressions, holes and grooves in order to improve adhesion (Fig. 12). This can be observed especially on the back of the thin plaster (maximum 1 cm.) used for figural representations on a smaller scale. The backs of some plaster pieces show reed or mat structures or imprints of wood (Fig. 13). Furthermore, the cord imprints, applied originally on the wet plaster, are visible (Fig. 14). Borders of walls or frames of windows and niches, architectural facade imitations and patterns were planned with the help of parallel cord imprints made in the still wet, smoothed surface. Patterned floor paintings can also be found. Fragments of these can be identified through the absence of brick impressions on their backs. Moreover, the plaster is comparatively thick and even, with edges which curve upwards.

The following preliminary classification of plaster for wall paintings at Tell el-Dab'a can be suggested, and four to five different types (A, B1-2, C and D) differentiated (Figs. 7-11). The plaster was generally applied on clay bricks, and the spaces between these bricks filled with balance plaster. In cases A, B and C, a coarse plaster with a coating of smoothed coarse plaster on top was applied directly on the clay bricks.

In the case of A (Fig. 7), the first coarse plaster was applied unevenly, but is also recognisably uneven in the case of B. The reasons for this can be seen in the better adhesion it offers for the smooth coarse plaster which overlies it.

Type A is characterised by the application of a drawing or sketch, very loosely carried out in red colour, on the smoothed coarse plaster (Fig. 15). The drawing could also be used in the composition or scene, and in this case runs into the compressed smoothed plaster coating which was put on the smooth coarse plaster. The basic layer of colour (described as colour application, for example in Fig. 10) was put on these compressed plaster coats. Areas of white were added to this basic coat of colour and show demarcation lines between various scenes (Fig. 16).

In types B1 and B2 (Figs. 8-9) both these coarse plaster coats were applied to the entire area of the clay bricks, except in the case of the small figural scenes. In this type (B2) another unusual feature, which applies to all small figural scenes (coloured red in Fig. 9) could be observed. These show as a base a very thin, smooth fine plaster with raised 'dovetails' which fit, like a relief, into the depressions of the loam filling below (see Fig. 8). No example of a plaster coating showing suitable depressions could be found, which is why a loam filling can probably be assumed. The technique of construction must have been as follows. First the large scenes with their layered coarse plaster coating were applied, and the little scenes left blank. Then the loam coating with pointed depressions was applied. The edges of the plaster of the large scenes were given a slope, as the spaces thus created were filled with plaster only after the completion and drying of both scenes.

Sloped plaster edges have also been found in the case of type C (Fig. 10), but they could have been a sort of working border, because immediately after the application of the smoothed coarse plaster a colour application (for example a light ochre shade) belonging to the scene on top followed without taking the borders into consideration.

Type D (Fig. 11) consists of a layer of coarse plaster. Raised decorations in high relief were executed in coarse relief plaster with fine plaster on top. Slightly raised scenes were executed directly in fine relief plaster (Fig. 18).

Distinct marks of tools (Fig. 19) have been found in the fine plaster of the scenes executed in coarse plaster relief. These tool marks indicate compression, with the aim of improving adhesion.

THE MURAL PAINTING

The Minoan mural paintings at Tell el-Dab'a can be divided into secco and fresco technique, and a combination of both in the case of overlap. One example may illustrate this: leaf ornaments show that the ground shade was applied relatively thickly in secco technique. On this the leaves were applied onto the lime, and fine details were added by means of lines (Fig. 17). Another method of application can be observed, for example, in the case of a fragment showing a piece of cloth(?), which was executed purely in fresco technique on wet plaster (Fig. 20).

One thing should be noticed in connection with technique and execution: it is often difficult to tell whether a fragment was executed in fresco or in secco technique. This is because the conditions of preservation, which depend on the find circumstances, often make this impossible. An additional problem is caused by overlaps and interpenetration of the individual coats of paint. As objection to the view that all wall paintings were executed in fresco technique, the following may be remarked. The floor and the labyrinth pattern, as well as various other rectilinear architectural elements in the painting, were imprinted on wet, smoothed plaster to provide a rough layout of the picture. When the colours were applied, the plaster was already dry. Moreover, the colours were applied too thickly for fresco technique (often 1 mm. in thickness). In true fresco technique, the layer is comparatively thin and bonds well with the wet plaster surface without the use of adhesives. In secco technique the various comparatively thick layers of colour (as at Tell el-Dab'a) were strengthened with adhesives to preserve their intensity and to allow easier smoothing of the surface.

 The basic colours in particular, like blue, red, black and ochre, were applied on a large scale with a spatula. The fine, superimposed paintings were executed with a brush.

 The bright tones were mixed with lime, and a soluble gum arabic, which has all the necessary advantages for this technique, may have been used as an adhesive. In this way, the colours keep their dear intensity and acquire a pasty consistency which allows them to be applied and smoothed easily. After drying they become quite hard and durable.

The relative frequency of the colours used for the Minoan mural paintings at Tell el-Dab'a can be seen in the following chart (Table 1). Further comparisons with Minoan paintings will be necessary in respect of these.

The constituents of the various kinds of mortar and pigments show that in one case (H-V) an egg adhesive and in another case (H-IV) a casein/glue adhesive were used for the colour pigments (Table 2). Analysis is very difficult, however, because the soil of the excavation site consists of elements similar to those of the adhesives.

In all cases it is a matter either of pure lime plaster or lime plaster with additions of quartz sand with grains of ilmenite and dolomite.

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