Because rock art conservation and site management is such a new and
underdeveloped field, sound policies in this area are far from firmly
established. There is a clear lack of basic research into almost any
facet of this field and therefore underlying policies remain very much
in flux. A few specific points are considered to illustrate this.
Termite tracks and the nests of a variety of mud-daubing wasps are such a common feature at tens of thousands of rock art sites the world over, that they have long attracted the ire of site managers in all continents except Europe. Just ten years ago we had clear expert recommendations by entomologists on how to deal with such ‘infestations’ (Watson and Flood 1987; Naumann and Watson 1987). For instance, the mud nests were to be removed because of aesthetic concerns and the damage they do to rock paintings, but also because the presence of wasp nests tends to attract the construction of more nests. Since the recent introduction of luminescence dating of quartz grains contained in these nests (Morwood et al. 1994; Roberts et al. 1997, 2000) it has become apparent that such research can only be conducted if these structures have remained intact. Much the same would apply to termite tracks. Moreover, at least in northern Australia it has been shown that rock paint-ings occur not only under wasp nests, but are often found painted over remains of such structures which may have survived for millennia. Naturally they may also contain organic matter, which can be dated. At some sites, notably in South America, the interstitial spaces in wasp nests have become mineralised, resulting in fossilised wasp nests that are as hard as limestone. One would certainly not recommend their removal, particularly as they are likely to yield considerable environmental information about the past if appropriately analysed, and are no doubt datable.
In the very short time of a decade, our attitude to insect structures at rock art sites has changed dramatically, from the fundamental doctrine of banishing from the vicinity of rock art everything that might possibly interfere with it, or with our ‘aesthetic appreciation’ of it, to the present, better informed attitude. This raises two relevant points: firstly, our knowledge of the extent of actual damage to rock art was based on conjecture, not on sound research in most cases. Secondly, the overriding consideration was the enjoyment of the human visitor: how easy the art is to see, how photogenic it is.
Precisely the same applies to the removal of lichen. As noted in Lichenometry, lichen can be useful in the dating of rock art, and in most circumstances there is no evidence that they contribute to deterioration of rock (Smith 1962; Walderhaug and Walderhaug 1998). Some lichenologists argue that lichen may reduce weathering rates, and there can be no doubt that they reduce anthropic damage where they conceal the petroglyphs successfully. Jackson and Keller (1970) report that the ‘weathering zone’ under lichens is thicker than adjacently, but this is to be expected. There would be little erosion under the lichens, while the unconcealed surface may well have been subjected to disintegration. Subsequent examination of the same site by Berner (1992) showed that Jackson and Keller’s ‘weathering zone’ was in fact a deposit of aeolian dust. According to Cochran and Berner (1992, 1993) there was absolutely no evidence that the lichens are preferentially attacking their support rock or enhancing its breakdown. Evidence concerning the effects of lichens seems limited to such chemically fragile rocks as limestone (Wainwright 1985) and shale (Fry 1924, 1927). Better metamorphosed facies, beginning with schists, are probably not much affected by lichens, especially where thalli are thin and patchy. Chemically resistant rock types apparently benefit from lichen cover in that it protects them. The occurrence of loose flakes beneath lichens is not evidence that it was caused by them, which is in fact unlikely; it is the lichen that has held such clasts in place. Most lichen species use the rock only for support, deriving their nutrients from airborne detritus. This is demonstrated by their ability to colonise inert surfaces such as pure quartz, aluminium, fibreglass and galvanised steel roofs. I have microscopically examined the surface of terracotta roof tiles that had been covered by lichens for about a century and have detected no corrosive traces that might be attributable to these plants.
Ten or twenty years ago, the construction of buildings to house rock art in situ was considered in quite a number of countries — and sometimes implemented without any comprehensive independent consultation. The placement of such buildings is one of the two basic forms of ‘massive intervention’, the other being the sawing off and removal of whole panels to transport them to a museum, which was last proposed in the Côa valley in Portugal, and defeated. The problems encountered in three such structures erected over petroglyph panels, in Canada, Russia and Sweden, have been reviewed (Bahn et al. 1995, 1996; Bahn and Hygen 1996). In all three cases the buildings are considered to be failures, primarily because massive intervention involves the creation of entirely different environmental conditions than those in which a rock art panel has managed to survive for centuries or millennia. While the rock art was certainly suffering some damage under conditions of natural weathering, the ameliorating effect of placing it inside a building may easily be negated by new threats due to new conditions which the rock had not previously experienced. Thus deterioration may well be accelerated by massive intervention. Again, a strategy of past years has become questionable after close scrutiny.
This applies also to the use of air abrasive equipment (Ford 1995) in emphasising patinated petroglyphs. Some years ago this method was applied to petroglyphs in the Sydney sandstone area of Australia, until members of the public objected and complained to an independent scholarly organisation, the Australian Rock Art Research Association. The practice was then discontinued, but the use of such equipment is still being advocated occasionally. There are legitimate applications for it, especially in the removal of modern graffiti — but once again we can see that the activities of rock art conservators need to be monitored by open peer review, and prac-titioners themselves need to be sensitive to such discussion. Another example is the widespread notion that graffiti beget more graffiti, hence to remove the existing graffiti may eliminate the motivation for the graffiti artist. This may well be true, but is at best a general rule of thumb. As detailed above, it has also been found that, when a small area in a graffiti-covered site was cleaned, within a year new graffiti appeared in the area left vacant by the graffiti removal (Bednarik 1992b).
An important recent development in rock art conservation work is the emerging emphasis on monitoring. In the past, resources were usually only made available for the duration of a particular project, and once this work was completed there were no funds and there was no further interest. Rock art preservation and site management measures need to be monitored over very long time spans. For the benefit of the global specialist community, both positive and negative effects must be determined and objectively reported. Without such measures, mistakes would be repeated over and over, thousands of times. Detailed follow-up technical reports are therefore required, and they need to be rendered accessible to the rock art conservators of the world. In view of the tendency of governments to re-organise their technocracies at rather regular intervals it is evident that no state agencies can be entrusted with such a long-term responsibility. Rather, universities and scholarly societies (specifically, the members of IFRAO) need to be entrusted with the necessary vigilance to ensure that such long-term monitoring is not neglected. Such monitoring is greatly facilitated by modern digitised equipment, which offers the benefit of facilitating types of research largely neglected until now: the measurement of surface retreat on fragile rock such as sandstones, the monitoring of weathering processes generally, of paint residue colours and of patination, among other variables.
A matter related to monitoring is the need to ‘finger-print’ interventions in rock art, in the way pioneered by Thorn (1993). Graphical documentation has long been considered appropriate, but Thorn introduced a new way of identifying interventions: by including in substances applied (such as paints or varnishes) materials the skilled researcher can readily identify as modern. For instance glass micro-spheres, ranging in size from 10 - 200 m, are readily identifiable microscopically and by x-ray diffraction. They can be included in substances applied by the conservator, indicating that the intervention must postdate 1972 (when the glass spheres were first made). Similarly, certain colours used in toning incisions (e.g. synthetically manufactured ochres known as Mars colours, titanium white, manganese blue, platinum yellow) only became available at specific times in modern history, and they are readily identifiable microscopically. In contrast to the pigments used in pre-History, which contain many incidental inclusions, these synthetic substances are pure and of even particle size.
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