. Can. J. Chem. 65, 1058 (1987).The once colourful mural paintings at the Beni Hasan tombs (ca. 2100 B.C.), an important Egyptian archaeological site, are covered with an obscuring grey deposit. Qualitative observations made over the past 150 years were assembled and correlated with each other by us. Cumulatively, they indicate that recently the development of this layer has accelerated. To study this surface degradation, X-ray photoelectron spectra of fragments from the painted walls have been collected. Empirical XPS sensitivity factors have been employed to treat the data semiquantitatively. Three types of surfaces were identified. The first surface consists of CaC03 and Si02 as major constituents, and was the only surface identified previously. Our XPS data indicate that it also contains AI2o3, NaCI, MgO, sulphates, and phosphates as minor and trace components. The second surface consists predominantly of aluminium silicates. The third surface consists mostly of calcium carbonate. A preliminary mechanism for opaque layer formation is proposed herein. It suggests that the principal physicochemical processes are adsorption of water in the presence of carbon dioxide, followed by dissolution of the substrate walls upon which the murals were painted. This mechanism is consistent with our finding that mural deterioration is recent; it also indicates that deterioration is progressive, continuous, and cumulative. Further experiments are designed to verify the proposed mechanism. Two mechanisms proposed earlier are found to be inconsistent with at least some of our findings. Relatively recent efforts in removing obtrusive surface layers with dilute HC1 were found to be performed carefully; there was no evidence of excess chlorides on cleaned surfaces. However, this finding does not provide a guarantee that murals were undamaged by HCI below the surface. It does suggest that progressive damage due to the formation of hygroscopic CaC12 on the surface has been avoided. Chem. 65, 1058Chem. 65, (1987.Les peintures murales trks colortes des tombes de Beni Hasan (environ 2100 B.C.), un site archCologique Cgyptien important, sont couvertes par un dCpot gris qui les rend moins claires. On a rassemblt et Ctabli des corrtlations entre les diverses observations qualitatives qui ont Ct C faites au cours des 150 dernikres annCes. Ces observations prises d'une maniere cumulative indiquent que le dCveloppement de cette couche s'est rCcemment acctlCrC. Dans le but d'ttudier cette dtgradation de la surface, on a recueilli les spectres photoClectroniques par rayons-X de fragments provenant de la peinture des murs. Dans le but de faire un traitement semi-quantitatif des donntes, on a utilisC des facteurs empiriques pour la sensibilite des SPX. On a identifie trois types de surfaces. Les constituants principaux de la premikre sont le CaC03 et le Si02; il s'agit de la seule surface qui avait CtC identifiCe antkrieurement. Nos donntes de SPX indiquent qu'elle contient aussi du A1203, du NaCI, du MgO, des sulfates et des phosphates, comme...

The Egyptian tombs at Beni Hasan (ca. 2100 B.C.) have developed an ubiquitous, progressive grey surface layer which disfigures their painted surfaces. Recently, we published a series of X-ray photoelectron spectra of samples from these tombs and proposed a mechanism for surface layer formation. It involves COz-saturated condensed water which gradually erodes the mural substrate. However, no direct evidence for this erosion was available. To test the proposed mechanism, light microscopy was used to study cross-sections of the murals. Areas of repeated solution and precipitation, in the form of dendritic structures were discovered in the subsurface regions, especially in yellow pigmented samples. In red pigmented samples, this degradation is not seen to the same extent. A series of electron microprobe analyses of the surface and subsurface regions of small painted fragments also were performed. Porous, heterogenous subsurface regions with pockets of phosphates have been found, predominantly in the yellow samples. These findings support the mechanism proposed earlier. Pore size measurements, estimated by photographic measurements, indicate that subsurface alteration took place before the bulk of the surface deposit layer had formed and that the existing surface deposit protects, as well as obscures, the painted walls. The surface layer development described here has some aspects common to other natural systems, i.e. the interaction of C 0 2 in water with carbonate-bearing rocks and deposits. However, at Beni Hasan there is effectively no source of groundwater and the painted surfaces are sheltered from direct exposure to the environment. Therefore the Beni Hasan deterioration has unique mechanistic features. Chem. 66, 2348Chem. 66, (1988. Les tombes tgyptiennes ii Beni Hasan (environ 2100 B.C.) ont developptes une couche superficielle grise qui dtfigure progressivement les surfaces peintes. Rtcemment, on a publiC une strie de spectres photo-tlectroniques des rayons-X effectuts sur des tchantillons provenant de ces tombes et on a proposC un mtcanisme pour expliquer la formation de ces couches superficielles. I1 implique de I'eau saturCe par du C 0 2 qui provoque une trosion graduelle des murales. Toutefois, on ne posstdait aucune donnte directe concernant cette trosion. Afin de verifier le mtcanisme propost, on a utilisC la microscopic lumineuse pour ttudier des sections droites des murales. Sous la surface, on a dkcouvert des surfaces ayant subi des solutions et prtcipitations rtgtCes, sous la forme de structures dendritiques et particulibrement dans les Cchantillons pigmentts avec du jaune. Dans les rtgions pigmenties en rouge, on n'a pas observe un tel degrt de dkgradation. On a aussi effectut une strie d'analyses par micro-sondes tlectroniques ii la surface et dans les regions sous la surface de petits fragments peints. Dans les Cchantillons pigmentks en jaune, on a observt sous la surface des regions poreuses et hkttrogbnes qui foment des poches de phosphates. Ces rtsultats sont en accord avec le mtcanisme pr...

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During the heights of ancient Egyptian civilization, statues of deities and pharaohs were often constructed of hard and colourful igneous rocks, such as granite and diorite. Most of these statues remain in an excellent state of preservation. However, others have unexpectedly fragmented, in some cases only a few years after having been excavated in near-perfect condition. In the present work it is shown that two interrelated physicochemical processes contribute to this degradation: (1) the infiltration of saline H2O and (2) subsequent alteration of the constituent minerals. Conclusions were reached on the basis of neutron activation and atomic absorption analyses of rock samples from two sites in Upper Egypt and leached soluble salts therefrom. These samples were identified as quartz diorites on the basis of petrographic and X-ray spectroscopic examination. The chemical significance of the geological nature of the stone is discussed. Possible precautions to be observed in the field are presented.

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