Accumulation of soot layers on the ceilings and walls of ancient Egyptian tombs and temples is a very common phenomenon. In the Roman period, numerous isolated tombs and temples, dating back to the Pharaonic period, were inhabited by Christian hermits. When they suffered from persecution and economic pressure by the Romans, these sites served as shelters for them and consequently some of these pagan sites were turned into churches [1, 2]. As a result of that occupation, the wall paintings of these Pharaonic sites became begrimed with thick soot layers produced by the domestic activities of the new inhabitants (cooking, lighting, heating, etc…). In addition to the adsorption of various pollutants, these soot layers obscure the wall paintings and reduce the permeability of their surface; [3, 4].
Numerous reagents have been used for the cleaning of soot and smoke particulates from artwork surfaces. They include solvents, salts, and surfactants [5, 6]. The most commonly used reagents are as follows: a) solvents such as ammonia, ethanol, white spirit, acetone, trichloroethylene, and ethyl acetate, b) surfactants such as orvus, vulpex, and triton X-100, and c) salts such as sodium bicarbonate, ammonium carbonate, sodium carbonate, tri-ammonium citrate, and ethylenediaminetetraacetic acid (EDTA). Traditionally, they are used individually or in mixtures and applied by cotton swabs or poultices [5–9]. As an example, in a recent study, Zn nanoparticles mixed with vulpex was successfully used to remove soot, patches of waxes and blood from the wall paintings in the temple of Isis in Luxor, Egypt [3]. In another study concerning conservation-restoration of the mortuary temple of Ramses III in Luxor, enzymes were used to remove soot deposits, blood of bats and a deteriorated varnish of animal glue applied as a protective coating in a previous conservation treatments [10].
In our study, cleaning tests were performed on the ceiling of the Osiris sanctuary in the temple of Seti I at Abydos, Egypt. Seti I dedicated one of the seven sanctuaries in this temple to the god Osiris. Osiris is one of the most important and popular gods in ancient Egyptian history. This importance is derived mainly from two circumstances. The first one is that he suffered a dramatic death: either by drowning or by being murdered by his brother Seth. According to the myth, his corpse was dismembered and then reconstituted and mummified by his wife Isis and his sister Nephthys. Isis, after becoming impregnated by the mummified Osiris, gave birth to a son Horus who was secretly raised by her to protect him from his uncle, and upon reaching maturity, Horus managed to triumph over Seth and was crowned king of Egypt. This myth is significant as it ensured Egyptians that they could survive after death. Secondly, Osiris was popular due to the fact that, after the victory of his son, he was installed as the ruler of the netherworld where every deceased Egyptian had to travel through for regeneration after death. The cult of Osiris was connected to Abydos (situated in Thinite province – upper Egypt) in addition to Busiris (situated in the east – central Delta) [11–14].
The sanctuary of Osiris is the most interesting one in the temple and is located in the middle of a series of seven sanctuaries devoted to different deities; see Fig. 1. All the sanctuaries contain false doors on their west side except for the Osiris sanctuary that has a real door. The latter leads to a complex of small rooms dedicated to the celebration of the Mysteries of Osiris.
The scope of this work is to evaluate the use of gels, as a controllable and safe cleaning method, for removing thick soot layers from the ceiling of the sanctuary of Osiris without provoking damage to the sensitive paint layers underneath (see Fig. 2). In previous studies, we developed a polyvinyl alcohol-borax/agarose (PVA-B/AG) double network gel and studied its properties. It was tested to remove deteriorated consolidant layers from wall paintings of the same sanctuary and it was able to successfully remove the consolidant without damaging the paint layers [15]. In addition, we investigated the different characteristics of the PVA-B/AG double network gel. According to these investigations, the gel is characterized by the following features: a) it is a flexible gel with the ability to adapt its shape to complex surfaces such as the case of ancient Egyptian painted reliefs, b) it features good shape stability when applied on painted surface for extended contact times, and c) it can be loaded with a wide range of reagents such as mixtures of polar and non-polar solvents, chelating agents, and surfactants, d) and it has a good liquid retention, a relevant property in sites at elevated temperature and at (very) low levels of relative humidity [16].
Based on the aforementioned features, the PVA-B/AG double network gel was deemed suitable for cleaning tasks in the sanctuary of Osiris. For this reason, the gel was loaded with various cleaning reagents, already documented in literature to have the ability to remove soot particles. The prepared gel composites were applied to the ceiling of the Osiris sanctuary during two cleaning tests and the results were assessed visually and microscopically. In view of the difficulty of reaching the cleaning locations (curved ceiling ca. 4 m above floor height), the option was taken not to use other/more sophisticated (spectroscopic) characterization equipment on site to assess the difference before and after treatment. The most effective gel composite was adopted to treat a larger area of the surface as a final demonstration of its efficiency.