Growth of desert varnish on petroglyphs from Jubbah and Shuwaymis, Ha’il region, Saudi Arabia

Petroglyphs, engraved throughout the Holocene into rock varnish coatings on sandstone, were investigated in the Ha’il region of northwestern Saudi Arabia, at Jabal Yatib, Jubbah, and Shuwaymis. The rock art has been created by removing the black varnish coating and thereby exposing the light sandstone underneath. With time, the varnish, a natural manganese (Mn)-rich coating, grows back. To study the rate of regrowth, we made 234 measurements by portable X-ray fluorescence (pXRF) on intact varnish and engraved petroglyphs. Since many petroglyphs can be assigned to a specific time period, a relationship between their ages and the Mn surface densities (DMn) of the regrown material could be derived. This relationship was improved by normalizing the DMn in the petroglyphs with the DMn of adjacent intact varnish. In turn, we used this relationship to assign a chronologic context to petroglyphs of unknown ages. Following the removal of the varnish by the artist and prior to the beginning of Mn oxyhydroxide regrowth, a thin Fe-rich film forms on the underlying rock. This initial Fe oxyhydroxide deposit may act as catalyst for subsequent fast Mn oxidation. After a few decades of relatively rapid growth, the regrowth of the Mn-rich varnish slows down to about 0.017 µg cm–2 a–1 Mn, corresponding to about 0.012% a–1 Mn of the intact varnish density, or about 1.2 nm a–1, presumably due to a change of the catalytic process. Our results suggest that petroglyphs were engraved almost continuously since the pre-Neolithic period, and that rock varnish growth seems to proceed roughly linear, without detectable influences of the regional Holocene climatic changes.

A Black-figured Hydria of the Polygnotan Period

In 1903 the Russian Archaeological Commission purchased a hydria from a dealer at Olbia which is now in the collection of ancient vases in the Hermitage (Fig. 1). Being considered by some authorities a forgery, the vase was not published in the Report of the Commission. I can assert that there is no doubt as to the authenticity of the vase. Apart from small injuries there are no important parts broken off or restored. The shape, but for some slight variations, is that of a typical late archaic hydria; sharp divisions are avoided, the shoulder being connected with the body by a soft curve and the same profile used for the foot. The ring above the foot is quite flat and not separated from the foot. On the lip of the vase there are two sharp projecting tongues instead of the “rotelle” of the archaic type (Fig. 2).The handles are round and curved slightly upwards. The varnish is very bad and dull, being laid on very thin, so that the surface of the clay shows through. There are spots where the fire has turned the black varnish red. The clay is of a dull yellow colour, badly cleansed, with holes in the polished surface, evidently in consequence of small stones and pieces of glimmer which have broken away. The surface of the clay, in the panel reserved for the design, is of a reddish colour. The greater part of the foot, the stripes under the horizontal handles, the inner parts of all three handles and the outer part of the lip are left unvarnished. Judging from the quality of the clay and the special character of the varnish, the vase appears to be Etruscan work.

A Vase Fragment from Orvieto

Perhaps an apology is due to the readers of the Journal of Hellenic Studies for venturing to call their attention to so fragmentary a vase as the one depicted in the accompanying illustrations, Figs. 1, 2; the excuse must be that the design offers certain points of interest which make one regret its mutilated state.All that are preserved are the stem and part of the interior design, cm. 5·5 × 4·8, of a r.-f. kylix which was purchased at Orvieto and purports to have been found there. The clay is fine and well worked, the black varnish of the stem of a brilliant lustre. Of the exterior design there remains only a small section of the ring indicating the ground, and one long, slender foot.