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THE
SILTED-UP CHAMBER
The entrance to the Silted-up Chamber
lies at the far end of the Great Fissure, on the lower left side, 3
metres below the top of the scree cone. Twelve metres long and 6 metres
wide, the Chamber resembles the entrance zone of the cave in its
morphology, although the very significant sandy filling hides this
similarity. The rock here is extremely gritty and friable, with numerous
scars left by exfoliation. For these reasons the walls were never
decorated, or at least we have never discovered any engraving or trace
of colouring matter. A partially blocked corridor, some 20 metres long,
leads off the Chamber.
The Rock
Support
The search for and selection of suitable
surfaces for graphic expression was determined by various factors: the
mechanical properties of the rocks, for instance, the morphology of the
support and the accessibility of the walls. Palaeolithic man had to
gauge these different data and then adapt to the circumstances.
Other factors also entered the equation,
such as the dirtiness of the walls. Particles of dust are in constant
circulation in the atmosphere and often settle on horizontal surfaces.
This contamination, which sometimes changes the colour of the wall from
a very pure white to dark brown or anthracite grey, can radically reduce
the wall's reflective properties. Palaeolithic man clearly took this
into account: there are virtually no paintings or engravings on such
sloping surfaces, particularly in the Hall of the Bulls, the Axial
Gallery and the Nave where the decoration is concentrated on the
overhanging level above.
The morphology of the walls results
either from the removal of material, by chemical or mechanical
decomposition, or from the addition of material by re-crystallization,
with or without the incorporation of the residual fill of the cave
(particularly clay). Human action reflects this duality as a rock
surface is either incised, in order to engrave a line or scrape a
surface, or added to in the form of a painting or drawing. The texture
of the support and its relief played a major role in deciding which
technique or tool to use, as well as determining how well works were
preserved over time.
27 Substrate with a powdery surface.
The character of this surface is linked to the very gritty nature of the
rock, caused by carbonate and silicate particles rendered friable by
corrosion. It extends through the entire southern part of the cavity,
from the Passageway to the Chamber of the Felines.
Detailed analysis of the rock supports
reveals a great deal of variability in surface conditions. At Lascaux
more than a dozen different types have been isolated in this way. They
are distinguished by their granularity, their hardness, their morphology
and their reflectivity. We have defined these types as 'forms': They are
divided into two basic categories: one relates to the solid rock, and
the other incorporates the coating elements that have been added during
the course of the evolution of the cave (clay, calcite or other
secondary products).
28 The carbonate encrustation here
takes on a form characterized by spicules, small calcite needles that
grow in all directions. This type of surface is found primarily in
the Hall of the Bulls.
In the first category, the surface
condition is the result of decomposition, either by erosion or by
corrosion, or most often by a combination of the two. Most of the time
the chemical factor obscures the mechanical effects of water or
exfoliation, which are always very close to the intersections between
strata. This is the most common type of form and covers approximately
two thirds of the total surface of the cave. Granularity, but above all
the degree of hardness of the material, characterizes these wall
surfaces, which are also the most susceptible to decomposition. Many
were engraved. The most fragile supports are characteristic of the
entrance zone, the Silted-up Chamber and its extension. The rock is
plastic for 1 to 2 centimetres and heavily saturated with water, which
is not conducive to the long-term preservation of paintings or drawings.
Nevertheless, engravings should have been able to survive, but we have
discovered no trace of them. Proximity to the entrance may explain this,
as this zone is rarely decorated.
Powdery surfaces are the most common
(ill. 27). A certain surface weakness is evident on this fairly dry type
of support. Effects of corrosion remain superficial and limited to the
upper few millimetres of the much harder rock. It is repeatedly
transected by fissures filled with calcite, which is more resistant and
thus remained in slight relief, as on the panels of the Swimming Stags
or the Great Black Cow. The presence of iron oxide in the limestone
gives it an ochreous colour, which, reduces its reflective properties.
Concretions in the Hall of the Bulls and
the Axial Gallery are riddled with the scars of exfoliation, where the
surface of the walls has flaked off. They are generally found at the
boundaries of stratified layers and may be caused by tension in the
rock. There, the reflection of light is much weaker than on the surface
of the concretions, reducing the contrasting effect of colour and thus
giving a certain unevenness to the image.
The second category, associated with the
deposit of clay and, above all, calcite, affects much of the Hall of the
Bulls and the Mondmilch Gallery and the entire Axial Gallery. There are
also small islands of calcite along the first few metres of the
Passageway. For the most part, these surface conditions result from
chemical processes caused by reactions between percolating water, the
limestone and carbon dioxide, which is always in a high concentration in
this environment. These forms are found most often on the primary
surface, but they also affect secondary phenomena, such as deposits of
clay. Differences in the level of hardness are so insignificant in this
case that it is less relevant as a determining factor. The granularity
is far more important: the choice of technique used to execute the
figures will often be governed by the extent and configuration of the
microtopography of the support.
The most important form at Lascaux is the
spicular one (ill. 28), not in terms of its extent within the cave,
which is restricted to the Hall of the Bulls, but because of ies
exceptional photometric properties. It is created around calcite
needles, between 3 and 5 millimetres long and with a diameter of less
than 1 millimetre, which are grouped together in small adjoining
clusters. The coherence of these surfaces is disturbed only by
infrequent gaps, most of which have been filled by a transparent calcite
flow. This form covets three quarters of the middle band of the Hall of
the Bulls, and there is only one discontinuity (the corroded surface
between the hindquarters of the fifth bull and the head of the sixth).
The morphology of these concretions reveals minor and very localized
variation. Its exceptional optical qualities, with a higher coefficient
of reflectivity, compensate for the relative roughness of the
background.
The 'cauliflower' form (ill. 29) is
equally characteristic of Lascaux's walls. From just inside the
entrance, its distribution affects the entire Axial Gallery, with the
exception of the upper half of the first third of the gallery and the
ceiling of the following enlargement. It is also present at the entrance
to the Passageway and, discontinuously, along the left wall. There are
numerous indications that the entire ceiling of this last sector was
covered by this calcite at an undetermined period. Surfaces less exposed
to thermal and hygrometric variation still preserve this evidence,
particularly along the first 3 metres from the entrance and on both
sides of the gallery, where some large paintings of animals still
survive. The white surface has a macroscopically undulating appearance,
with randomly distributed, irregular elements measuring between 5 and 15
millimetres in diameter. The majority are solid, although some are
shaped like small hollow domes.
The 'rice grain' form (ill. 30) is found
less widely than its 'cauliflower' counterpart. However, it is the
main reason that the Lascaux works are of such a high quality. Its
relatively fine-grained texture and maximum reflective properties make
it the perfect background. Several of the most prestigious figures of
parietal art were executed on this support, despite a lack of
accessibility or constraints imposed by a distorted ceiling or wall. The
Axial Gallery's four red cows and the frieze of the Chinese Horses are
the prime examples. Indeed, only the first third of the Axial Gallery
has painted surfaces. Beyond this point, access becomes increasingly
difficult, precluding the continued exploitation of this type of
surface.
29 The more solid 'cauliflower'
concretions cover the walls in the lower part of the Axial Gallery.
30 At the other extreme, this
foundation with a micro-topography resembling grains of rice covers the
interior surface and the projections of the ceiling in the Axial
Gallery.
31 Due to its unstable plastic
properties, intimately linked to the surrounding hygrometry, mondmilch
is unsuitable for engraving and even more so for drawing or painting.
Calcite-covered clay, caused by sediment
fill, coats the ledge running around the lower part of the Hall of the
Bulls and has a very high optical density. As it dried, the fragmented
clay coating was broken up by carbonate infiltration. Subsequent wetting
of the walls removed the clay, leaving only its impression, which has
led to false interpretations of these phenomena as Palaeolithic images.
Alteration of the calcite results in two
differentiated forms, one due to corrosion of the encrustation, and the
other to chemical alteration of the surface, which develops into
mondmilch. The former has only been identified in the Passageway,
particularly along the left wall and on the ceiling. The second is very
localized and restricted to a section intermediate between the Nave and
the Chamber of the Felines. It extends 1.5 metres above floor level
along both sides of the gallery, which is 21 metres long and has an
average width of 1.2 metres. Only the basal part is affected by this
encrustation. As a result of a biochemical reaction over an undetermined
period of time, at least part of the stalagmite deposit developed into
mondmilch (ill. 31). The plasticity of this material, which forms a
milky, whitish mass, several centimetres thick and with a very irregular
surface, varies according to the degree of humidity of the underlying
rock. These properties made such walls unsuitable platforms for parietal
art. However, before the process of deterioration the underlying
stalagmite must have had more suitable properties. It cannot be ruled
out that Palaeolithic depictions once existed on these walls.
The transparency of the laminar form
makes it difficult to find. This calcite veil has concealed some
decorated areas, particularly in the Shaft and the Hall of the Bulls,
between the third and the fourth bulls. It replaces the spicular
encrustation in those parts initially exposed to corrosion, more
particularly at the intersection with the Axial Gallery.
The massive form is restricted to the
Hall of the Bulls and the Axial Gallery and is always present
intermittently. It is linked to the penetration of the coating of marly
by thinly scattered, small openings or fissures in the cave roof, which
let water drip through. This phenomenon encourages the growth of calcite
in the form of short, squat stalactites, some tens of centimetres long,
which develop in the hollows of the deep cavities of the roof. The only
concretion of this type in the Axial Gallery, immediately next to the
Great Black Bull, was formed as a result of a fissure that runs along
the ceiling in the central part of the gallery. In the Hall of the Bulls
they ate more numerous and visible on both sides of the horizontal ridge
that marks the uppermost level. Some of them rest on the projection of
this formation. above the second and the sixth bulls, and the others are
located below the overhang close to the third, fourth and fifth bulls.
One variant is formed by a crystallization of 'butterfly wing' type,
above the first bull's head. The conjunction of these calcite deposits
and the aurochs head theme, which is found as many times as this
concretion exists in Lascaux (i.e. seven), is quite remarkable.
The pedunculate form (ill. 32) only
applies to a small section of the subterranean space. It is found in two
areas: on the lower part of the left wall at the entrance to the Hall of
the Bulls and below the first projection to the left of the entrance to
the Axial Gallery. Its morphology resembles that of a club: it has
a distal excrescence 2 to 3 millimetres in diameter but can be over a
centimetre long. The only figure recorded in this environment is a small
silhouette of a horse painted in black.
Even less common is the rhomboid form
(ill. 33), which is the result of the juxtaposition of macro-crystals
measuring some 8-10 millimetres along their edges. Its surface area is
limited to some tens of square centimetres at the entrance to the Hall
of the Bulls, on the lower ledge of the left wall.
32 The pedunculate form of
calcite outgrowths is only found over a small area of the Hall of the
Bulls and the Axial Gallery.
33 Even more infrequent is the
macro-crystalline type, found only on the left wall close to the
entrance to the Hall of the Bulls.
The heterogeneity of supports leads to
important variations in their characteristics. particularly in their
photometric properties. The ability of a surface to absorb light plays a
major role in determining how the parietal art is viewed. It is far
harder to make out a painting that absorbs more light than its
background, regardless of the colour of pigment used. partly because
those areas where the paint has been less thickly applied become less
visible. These factors had a huge influence on Palaeolithic man's
experiences of the cave, as they affected the type and importance of the
material used to light up an area. A chromatically dense wall implies
the concomitant use of several sources of light. This might explain the
abnormally high number of lamps recovered during excavations carried out
at the foot of the Shaft Scene. In a more favourable setting where the
surfaces are particularly reflective, such as the Axial Gallery or the
Hall of the Bulls, a single lamp would suffice to illuminate the entire
hall.
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