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State of
the Art Report: Rock Art and Semiotics
By Robert Bednarik
Prehistoric rock art represents by far the largest body of evidence we
possess of humanity's cultural, cognitive and artistic beginnings. Through
its relative permanence, it has profoundly influenced the beliefs and
cultural conventions of subsequent societies up to the present. It is
therefore an integral part of humanity's collective memory, and the
greatest surviving witness of our cultural evolution.
'Rock art' is a somewhat arbitrary term describing non-utilitarian
humanly made markings on natural rock surfaces, made either by an additive
(the application of material) or a reductive process (the removal of rock
material). The former result is called a pictogram or rock painting and
this form includes also pigment drawings, stencils and beeswax figures;
the latter is a petroglyph or engraving, sometimes called carving. The
term rock art is usually not applied to human markings on prepared or
dressed stone surfaces, such as may be found on buildings or rock-hewn
structures. Nor does it include humanly made but unintentional rock
markings (such as those occasioned by bulldozers), utilitarian rock
markings (e.g. drainage channels on axe grinding panels) or markings made
by non-human animal species, even if made 'deliberately' (e.g. certain
forms of cave bear claw marks in European caves). Broadly speaking, the
term rock art refers to anthropic (humanly made) markings on natural rock
surfaces; they may be pre-Historic or Historic (in the sense that the
capitalization of the term refers to the arbitrary definition of the
dominant society).
Rock art is a very widespread phenomenon on our planet, occurring in
nearly all countries. Its uneven distribution across all continents except
Antarctica is, however, not so much attributable to differences in
cultural conventions, it is primarily a taphonomic attribute (i.e. a
result of preservation bias). For instance, the high-pH and low
precipitation regimes of arid and semi-arid regions have greatly
facilitated the preservation of rock art in various parts of the world,
such as the Sahara, Arabia, central Asia, the American Southwest, Peru and
Australia. Another major determinant of rock art distribution is geology.
Some of the largest surviving concentrations are those found in the
sandstone facies of the former Gondwana plate, i.e. in southern Africa,
India, Australia and northwestern Brazil. These sandstone deposits have
facilitated the formation of rock shelters that provide excellent
preservation conditions, especially for rock paintings. Similarly, the
practice of Upper Paleolithic rock artists to place some of their
productions in deep limestone caves has significantly helped the survival
of some of that period's rock art.
Paleolithic cave art has been reported from over 400 sites, but the
art's attribution to the Pleistocene has remained intangible at many
sites. For instance, there is currently no validated claim for Paleolithic
rock art in central or eastern Europe, despite many such postulates having
appeared. Similarly, various claims made about the occurrence of
Paleolithic rock art at open schist sites in the Iberian Peninsula remain
unsubstantiated by dating evidence.
A brief historical review
The total number of known cave art sites worldwide is well under one
thousand, while the number of open rock art sites is likely to be up to
one million, and they often present vastly greater numbers of motifs than
the cave sites. Yet, in comparison to European cave art, their study has
been relatively neglected. For instance, no publication about Chinese rock
art had appeared in English until 1984, although the earliest literary
mention of rock art is from China. The philosopher Han Fei (280-233 B.C.)
provided the first known reference to rock art, while the geographer Li
Daoyuan (A.D. 386-434) described numerous rock art sites in China and even
mentioned occurrences in India. In South America, Captain De Carvalho
found rock art in 1598 in what is now Brazil, and published his recordings
in 1618, while in Europe, the first known recordings, made by Peder
Alfssön in Denmark in 1627, were not published until 1784. More determined
scholarly efforts commenced during the 19th century, focusing initially on
Russia, Scandinavia and northern Africa, later on southern Africa, parts
of South America, Australia and eventually India.
With the beginning of the 20th century, after orthodox archaeology
finally accepted the authenticity of Franco-Cantabrian cave art, the study
of rock art became nominally integrated into mainstream archaeology.
However, this merely promoted the proliferation of simplistic stylistic
constructs and the development of various unproductive methods. For
instance, some archaeologists considered that taxonomic constructs and
statistical analyses of stylistic or morphological matrices of motif types
would provide empirical interpretations, in the same way other artifacts
were classified and interpreted statistically. However, rock art has no
archaeologically perceptible time depth, and most major rock art sites are
cumulative assemblages deriving from different eras. Lumping these
different traditions together and treating them as a 'style' because they
happened to occur at the same place served no useful purpose, and this is
even before the complex issues of selective survival (taphonomy) are
considered. Thus the greatest barrier to integrating rock art successfully
into archaeology was the intractability of its dating. Worldwide, there
have been only about twenty instances of reasonably convincing minimum
dating by finding rock art under supposedly datable sediments.
Archaeological age estimations, generally by considerations of style
and 'content', have varied greatly for specific corpora. For example,
there is a distinctive tradition of shelter paintings in eastern Spain,
the Levantine genre. Over the course of the second half of the 20th
century it has been attributed to every single archaeologically perceived
cultural period from the Perigordian to the Iron Age (i.e. to every age
from about 35,000 to 2500 years ago), yet its true age, now thought to be
Neolithic or later, remains still unknown. Much the same applies
throughout Eurasia. In Portugal and western Spain, a corpus of engravings
known to be no more than a couple of centuries old was consistently
described as being from 20,000 to 30,000 years old. The 'oldest known rock
art site of central Asia', at Zaraut-Kamar shelter (Uzbekistan), is now
thought to have been painted in the 19th century, as is a series of
'Paleolithic' cave paintings in Mladec Cave (Czech Republic). These and
hundreds of similar examples suggest that age determination of rock art by
stylistic or archaeological means is tenuous at best.
The paradox is that, without some idea of its age, rock art has little
archaeological relevance, and it is difficult to separate components of
different traditions at sites. Some archaeologists have suggested that the
study of rock art should best be left to 'specialists'; others have
vigorously opposed this view. The last few decades of the 20th century
witnessed the emergence of rock art research organizations in many parts
of the world, beginning in North America, Australia and Western Europe. In
1988 these bodies formed the International Federation of Rock Art
Organizations (IFRAO), which currently has over forty affiliated member
associations, covering in effect most of the world. One of their principal
aims is to introduce scientific methods, grounded in such diverse
disciplines as geology, semiotics or cognitive science. This trend is
currently replacing interpretative endeavors with contextual studies, and
concerns with meaning are giving way to epistemological rigor.
Global distribution of rock art
The pre-eminence of the Franco-Cantabrian cave art has in some respects
overshadowed the appreciation of the many other rock art traditions of
Europe. In France, for instance, the extensive corpus of Fontainebleau
receives scant attention, simply because it is of the Holocene rather than
the Late Pleistocene. Much the same can be said about Spanish traditions,
such as the Galician petroglyphs or the Levantine paintings. Alpine
petroglyphs have fared somewhat better, especially in the western Alps at
Mont Bégo and southern Alps in the Tellina and Camonica valleys. There are
scattered sites or smaller concentrations in nearly all European
countries, but the only other major series of sites extends across
Scandinavia, from Denmark to Karelia. It comprises mostly petroglyphs, but
pictograms do occur, especially in Finland. Little is known about the rock
art of the Balkans and Greece, but there appears to be a fair amount of
it. Portugal, Britain and Ireland are well endowed with petroglyphs,
typically non-figurative. Most of European rock art has been attributed to
the Metal Ages, some may be older, and traditions that are more recent
certainly exist. It needs to be cautioned that credible dating is rarely
available, and revisions still have to be anticipated. For instance, the
Scandinavian petroglyphs are mostly attributed to the Bronze and Iron
Ages, but it is possible that more recent people, such as the Vikings or
the Saami, were involved in their making.
Asia, of which Europe is only a small appendage, comprises several
large bodies of rock art that surpass numerically any European regional
corpus. Most of the countries of the Middle East are rock art rich,
especially Saudi Arabia, Iran and Israel. Here, early inscriptions often
occur alongside petroglyphs, helping to unravel the chronology, and
suggesting that much of the art dates from between 3000 and 1400 BP. With
the advent of Islam, rock art production was severely reduced although
practices did continue. The rock art of the Caucasus region has only begun
to attract interest recently, and very little is known about Turkish or
Yemeni rock art. Researchers have noted the occurrence of concentrations
in Pakistan, but so far no research of substance has been conducted there,
while in the several countries to the north, it has only begun in the most
recent years. Across central Asia, including the Tibetan Plateau, there
are numerous reports of rock art, but a great deal has been destroyed by
Moslems, for instance along the Silk Road. Much better explored is the
rock art of Siberia, of which concentrations appear along the Yenisey
(impact petroglyphs) and Lena rivers (abrasion petroglyphs and few
paintings). In Mongolia, the greatest assemblages are found in the Altai
Mountains. The impressive iconography of the central Asian regions,
sometimes dominated by apparently human faces described as 'masks', or by
extraordinarily ornate 'deer stones', continues into China, especially in
the Ningxia Province and Inner Mongolia. Among the more than 10,000
Chinese sites, those in the north are almost entirely of impact
petroglyphs, while the situation is reversed in southern China. Nearly all
rock art there is of pictograms, especially in the rock art-rich Yunnan
Province, or in Guangxi Zhuangzu with its incredible site at Huashan,
where monumental paintings extend to forty metres height.
Japanese rock art is mainly found in small occurrences on boulders and
stelae, but information is often unreliable. The countries of South-East
Asia all feature rock art, but publications are very sparse and no
researchers have worked in most areas. A notable exception is Borneo, with
its numerous limestone cave art sites of paintings and stencils. In the
Philippines, sound ethnographic observations concerning cave paintings are
available from Palawan. India offers one of the largest and best-explored
rock art bodies in Asia, with paintings dominating in all provinces except
in the far north and northwest, in the Deccan and the extreme south. The
richest repositories are found in the rock shelters of the central
regions, particularly in Madhya Pradesh. They include the best-known
Indian site complex, Bhimbetka, of about 500 painted shelters.
Africa, too, boasts some massive rock art concentrations. These begin
with the several art regions of the Sahara, extending from Morocco to
Egypt. The arid conditions have greatly facilitated the preservation of
rock art of the last six millennia. In terms of its artistic finery,
Saharan art is matched by few traditions, one of them being the
Bushmen/San rock paintings of southern Africa. Other painting and
petroglyph traditions occur also in that region, and the Pleistocene finds
of portable paintings in Apollo 11 Cave, Namibia, imply that very early
traditions once existed. Other portable art from Africa is even older, but
no African rock art has been convincingly demonstrated to be of the Ice
Age. There are extensive corpora of rock art in Tanzania, Kenya, Gabon,
Sudan, and smaller occurrences in probably all remaining African
countries, but as in Asia, there are also great gaps in our knowledge of
distribution.
The situation is considerably better in Australia, where all major rock
art regions have been identified and the issue of antiquity is somewhat
clearer. The major bodies in the rock art-richest country are the
petroglyphs of the Pilbara, the paintings of the Kimberley and Arnhem
Land, and the mixed rock art of the Victoria River District and Cape York
Peninsula. Other notable complexes are the stencil-dominated sites of
central Queensland, especially in Carnarvon Gorge, the Sydney sandstone
petroglyphs and those of the Olary district in South Australia. In
general, the number of sites increases from south to north, with the
limestone cave art along the southern coast and in Tasmania forming an
unusual feature. A remarkably large part of Australian petroglyphs seems
to be of the Pleistocene, having been estimated to be as great as 20% of a
corpus thought to be well in excess of 100,000 sites overall. Many of the
islands of Oceania are also well endowed with rock art, among them New
Guinea, New Caledonia, New Zealand, Hawaii and Rapa Nui (Easter
Island).
Canada's rock art is comparatively sparse, with minor concentrations in
British Columbia and relatively isolated finds in most other states. The
United States, by contrast, has major occurrences, especially in the
southwestern states. The Chumash paintings and Coso Range petroglyphs in
California, the numerous sites across Utah, Arizona and New Mexico all
form a massive body composed of many traditions. Most other states also
contain rock art where suitable conditions pertain. In terms of antiquity,
North American rock art seems to be consistent with most of the rest of
the world: all or nearly all the rock art is of the Holocene. The western
art province continues in the neighboring Mexican states of Sonora and
Chihuahua, with notably impressive painting sites in Baja California.
Smaller concentrations occur in much of Central America, and there is
hardly a major island in the Caribbean that lacks rock art. In both
regions, paintings as well as petroglyphs occur.
All countries of South America feature rock art sites, but the major
corpora are found in the Andean region, from western Venezuela to
Patagonia. The largest single site is perhaps Toro Muerto in southern
Peru, consisting of several square kilometres of petroglyphs. Other
notable occurrences in Colombia, Bolivia, Chile and Argentina have been
subjected to detailed study, as have the extensive traditions of
northeastern Brazil.
The recording of rock art
Since rock art has begun to be recorded, centuries ago, the purpose of
such records has always been to create a visual register of those aspects
of the art that were deemed important. This has remained so until quite
recently, and it follows that rock art recordings are usually
interpretations of individual observers, not objective data. Indeed, this
principle is embodied in a ruling of the High Court of Austria in 2003,
that rock art recordings are copyrighted because they are individual
interpretations by the recorder. This is now changing with the
introduction of sophisticated digital recording systems that yield much
more objective results.
Nevertheless, the ready availability of computer equipment and
electronic image manipulating software does not necessarily obviate other
recording techniques. The discipline has in the past made the mistake of
ignoring useful approaches, such as rock surface cartography as initially
developed by François Soleilhavoup. It would be precipitate, therefore, to
jettison all earlier methods, but it is certainly appropriate to discard
all those that are invasive or threaten the research integrity of rock
art. Many of the latter have been used extensively in the past, but there
is absolutely no justification now to continue with any of them. These
physical enhancement methods have included the application of clear
liquids to close the pores of silica skins or other thin accretions, thus
improving photographic records. The liquids used in this have ranged from
water to motor oil, from kerosene to clear lacquer. Another common
practice has been the outlining of rock art with chalk and a variety of
other markers, including dye, pencil, lipstick, and felt pen.
Archaeologists have contaminated the geochemical fabric of thousands of
square metres of petroglyphs by applying organic white and black paints,
to facilitate manual recording. The use of pressure-sensitive films,
rubbings made with a great variety of materials, the production of casts
from latex, plaster of Paris, papier mâché, thermoplastic resin and so
forth have all been found to affect the rock art, and in some cases have
caused spectacular damage to it. The use of transparent film to copy the
art can also be damaging, because these sheets tend to be electrostatic
and the movement of pens or fingers can attract small flakes of material
from paintings. Even the use of aluminium foil tamped gently into
petroglyphs before it is backed by stiffer material, regarded as a
reasonably safe method, has at last been opposed by a chemist working with
rock art.
There is one very simple rule now in recording: unless the rock art in
question is about to be destroyed by other factors, no invasive method, no
contact is acceptable. The first consideration in all rock art recording
work must be that it would be selfish to prejudice any future analytical
methods rock art scientists will bring to bear upon the rock art,
centuries from now. Since we have not the faintest idea what these future
methods will involve, there is only one possible solution: all rock art
recording today must be by non-invasive methods, except in circumstances
where the rock art is subject to other imminent threats.
There is no need to resort to damaging and superseded methodology.
Photography, sometimes in combination with non-contact enhancement
techniques, is now universally available. Raking light photography
(oblique lighting at night) is far more effective in recording petroglyphs
than manual recording, which is a cumbersome and subjective procedure. It
can be most conveniently accomplished with battery-powered movie lights. A
variety of filters and special films are available to improve photographs
of rock art. Cross-polarized photography, using two light sources with
polarizing filters, can greatly enhance contrast. It is important that a
calibrated color and gray scale be included on all rock art photographs,
the most widely used being the IFRAO Standard Scale. This has a number of
purposes, the foremost being the facility of color re-constitution. All
photographic records are of distorted color, and all of them fade with
time, therefore a color profile included on a photograph permits the
digitized recovery of original color of the object at the time the image
was taken.
The equipment now widely available to rock art recorders includes
high-resolution digital cameras which, combined with the use of laptop
computers in the field, have revolutionized rock art recording.
Photographs can now easily be color corrected on site, as soon as they are
taken, right at the panel being recorded. The digital image processing
programs now available have replaced the laborious enhancement procedures
of the 1980s. In addition to this basic system, several more sophisticated
recording options have recently become available. Some remain very
expensive but, judging from previous experience, it is only a matter of
time before they, in addition, become stock-in-trade, and ever more
powerful tools are introduced at the high end. The use of photogrammetry,
which has been sporadic in rock art survey work, has experienced a revival
due to the introduction of digital elevation model (DEM) software. This
can generate accurate three-dimensional recordings of petroglyphs. An
alternative approach is the use of laser scanners to produce virtual
digital models of great accuracy and versatility. This technique evolved
from the need to record the topography of groove shapes, such as those of
Scandinavian rune stones. Manual groove topography of petroglyphs, still
done in the late 1990s, has now been superseded by automated laser
scanning. It yields visualization algorithms that facilitate the use of
such recordings in the application of computer-assisted drawing (CAD)
programs to rock art, which can create virtual rock art sites.
Micro-topography of rock art has also been attempted with a CCD camera by
obliquely projecting a grating fine grid (40 lines per mm) over the rock
art.
The alternative method of reproducing panels or sites is the production
of physical rock art facsimiles. This has been used for many decades, but
only sporadically because of the high cost involved. The most celebrated
rock art facsimile is Lascaux 2, a partial copy of the famous cave in
France. Having been created at the cost of $8 million, it is now viewed by
about half a million tourists per year and its cost has been recovered
many times over. Facsimiles are constructed by first acquiring the
necessary topographic data, traditionally either by photogrammetry or the
use of precision theodolites, but more recently by laser equipment. The
rock panel is then recreated and the rock art projected onto it. This
process is very laborious and involves considerable artistic skills.
Conservation and site management
Humanity lavishes billions of dollars annually on its art objects, art
repositories and art industry. By comparison, its endeavors to look after
its oldest and most valuable art treasures are miniscule. Despite its
appearance of relative robustness, rock art is quite fragile, and what we
see today is only the tiny surviving fraction of what was once created.
Two factors need to be distinguished in the deterioration of rock art: the
effects of natural processes, and the damage occasioned by human agency.
The mitigation of the former is often difficult, whereas that of anthropic
destruction is in most cases easily achievable. Importantly, deterioration
by humanly introduced factors far outweighs natural degradation. In
understanding the interplay between these two factors it is important to
appreciate that the rock art that exists today does so because it has
survived a great many natural decay processes, often surviving in a state
of relative equilibrium with its ambient environment. Hence, it is likely
to persist much longer unless there is a significant change in its
preservation conditions, especially one introduced by human intervention.
This may be as simple as the introduction of human visitation to a
formerly pristine site, or as complex as the occurrence of acid rain
caused by industrialization.
The principal natural agent of rock art loss is moisture, mainly in the
form of rainwater, capillary moisture in porous rock, condensation in
caves and shelters, freeze-and-thaw cycles, surface run-off, and secondary
effects such as salt efflorescence or exfoliation. Physical weathering of
rock art panels occurs as insolation (solar radiation), lightning strikes,
brushfires, Kernsprung, tectonic adjustments and kinetic damage (aeolian,
gravity or water induced). Many forms of biological factors can contribute
to weathering, including bacteria, fungi, lichens, algae, mosses, larger
plants, insects (mud-daubing wasps, termites, bees), nesting birds and
various larger animals, especially domestic and feral species. For many of
these threats, protective measures have been found. Site hydrology, for
instance, can be controlled by artificial silicone driplines in shelters;
condensation can be eliminated by climate control.
One animal, however, is causing far greater rock art destruction than
all other factors taken together. Of the many forms of damage occasioned
by humans the perhaps most repulsive is that occasioned by researchers, be
it through misguided recording activities or through their role in
permitting or condoning the destruction of rock art by industrial or
infrastructure development. The former has been largely eliminated in
recent decades, but the latter continues unabated. At one Australian site
complex alone, at Dampier, it has been responsible for the obliteration of
about 100,000 petroglyphs. Tourists and site visitors contribute to rock
art deterioration, though it has often been found necessary to sacrifice
some sites to them in order to preserve many others. The locations of new
sites are no longer made public, and well known pristine sites such as
Chauvet, Cussac and Cosquer Caves in France are totally closed to all,
except a few researchers who only enter these sites with careful
precautions to prevent contamination. For instance, researchers are not
allowed to walk on the floor of Chauvet Cave. In Australia, most of the
cave art sites are only accessible to two or three researchers and their
locations are generally confidential.
There are very few professional rock art conservators worldwide, and
the standards they apply vary from one region to another. Their tasks
include graffiti removal, moisture and climate monitoring and control, and
the design of site management measures. The latter differ according to
local circumstances, and include such measures as the erection of fences
to keep out animals, the installation of visitor boardwalks and paths, and
in some regions protective grilles. In modern site management practice,
the concept of 'site fabric' is paramount, referring to all physical and
non-physical aspects of a place, including accretionary deposits on the
rock, even its ambience or religious significance. The primary principle
of intervention at a rock art site is that any modifications must be fully
reversible. Today's site conservation and management practices may well be
superseded tomorrow, and the cultural resource in question is, after all,
not renewable.
The science of rock art
One of the priorities in contemporary rock art research is the
development of methods for estimating the age of rock art motifs. During
the 1980s, this led to the replacement of stylistic or iconographic dating
by forms of 'direct dating', in which the age of dating criteria
physically and directly related to the rock art is determined.
Propositions of the chronological relationship of these criteria with the
rock art must be testable, i.e. refutable. The dating criterion may be of
the same age as the rock art (e.g. an organic binder contained in the
paint residue of a pictogram, or the fracture surfaces caused by the
impact that occurred when a petroglyph was made); or it may be older than
the rock art (e.g. its support surface, or a lichen thallus dissected by
an engraved line); or it may be younger than the rock art (e.g. a
superimposed insect nest, or a mineral accretion concealing the art).
There are numerous types of such directly relatable criteria, most of
which have been provided by geochemistry so far. However, direct dating
offers no actual ages of rock art; it merely generates testable
propositions about the relevance of specific physical or chemical data to
the true age of rock art. The interpretation of this relationship demands
an understanding of the method used, of the circumstances of sample
collection, and of the limitations applying to stated results. The
principal difficulty experienced with this approach is that the
interpretation of its results is usually contingent on such complex
qualifications that they are difficult to relate to immediate concerns of
archaeology. To practitioners seeking certainties, expressions of
probabilities or intricate formulations of explanatory scenarios are
frustrating and seem to limit the practical use of such data.
The first method used in this quest was radiocarbon analysis of mineral
accretions containing atmospheric carbon, such as carbonates and oxalates.
These are often found in direct physical relation with rock art, but the
utility of their results is limited by a complex set of qualifications.
Uranium-series dating (thorium-uranium) has also been applied to
carbonate. Most widely used has been the carbon-isotope analysis of
inclusions in mineral accretions or in paint residues, and the
determination of the age of charcoal pigments. Here, the qualifications
are somewhat simpler. In the former method, the principal limitation is
that, to obtain valid estimates, the nature of the analyzed substance must
be determined, either at the object or molecular level. Until recently,
all such determinations referred to bulk samples, but in 2005, an Italian
team succeeded in isolating the dated substance molecularly in rock
paintings at five Libyan sites.
The determination of carbon ages of charcoal pictograms is a
straightforward method, but unfortunately, the date refers to the time
when the tree in question assimilated carbon from the atmosphere, not to
the time of rock art production. Ancient charcoal might have been used in
this, and often was, which introduces an obvious limitation to such
results. The most reliable results from any pictograms so far are 137
carbon isotope determinations obtained from beeswax figures in northern
Australia. An experimental approach is to use sand grains embedded in wasp
or termite nests directly related to rock art to determine when they were
last exposed to light, using the optically stimulated luminescence
method.
Petroglyphs may be more difficult to date than paintings, because they
offer no substance relating to the time of their execution. The mineral
dust then yielded is probably not recoverable. Nevertheless, the surfaces
freshly exposed and the mineral crystals broken or truncated at that time
experience significant changes over time, which are utilized in
microerosion analysis. Two forms of this method have been used so far: the
determination of erosion on rocks with components that weather at very
different rates, and the measurement of micro-wanes on fractured mineral
crystals. The second version is the more developed, but its use is limited
to very erosion-resistant rock types containing crystalline quartz, such
as granite, whereas sedimentary rocks are usually unsuitable. A very
robust analytical method, microerosion analysis yields reliable dates for
petroglyphs manufacture, but they are typically imprecise and several
preconditions need to be met. Recently, digital colorimetry has been
applied to both repatinated petroglyphs and pictograms, after surprisingly
consistent results were secured from historical inscriptions of known
ages. Other approaches, so far not effectively applied, would be to use
lichenometry or rock surface retreat for estimating the ages of
petroglyphs, or the use of weathering zone growth rates and macro-wanes.
There is thus considerable scope for extending the range of viable direct
dating methods.
While the scientific study of rock art may still be in its infancy, it
is not limited to issues of antiquity. Investigations of the technology of
rock art have involved several productive approaches, including the study
of the tools used in making petroglyphs, of paint recipes, of microscopic
inclusions found in paint residues, and of the sourcing of pigment
materials. Nano-stratigraphy - the microscopic excavation of strata of
paint residues, mineral accretions or weathering and patination zones -
was first introduced in the 1970s, and has been developed to great
sophistication already. Its principles are rather similar to those of
archaeological stratigraphy, but its methods, obviously, are very
different. To some extent, this method might even overcome the limitation
of rock art being, in contrast to archaeological sediment strata,
apparently two-dimensional. This potential is well shown by Alan
Watchman's extraction of ten radiocarbon ages from a stratigraphical
sequence of pigments and mineral deposits totaling only 2.11 mm thickness,
in north Queensland. The results were all in sequence, covering a period
of 26,000 carbon years.
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