In a cave or rock shelter excavated in limestone, water that is present at the interface (in the form of a film or droplets) and that is in chemical equilibrium with the calcitic facies will evaporate (Fig. 2). This calcite formation takes place under a variety of polymorphic conditions, the main micromorphologic patterns of which are shown in Table 1 (evaporatory conditions). An example of needles grafted onto preformed buds is shown in Figure 3. Methods used to obtain visual images and automatic
Figure 3
Growth of calcite crystals on a prehistoric painting.
Table 1 Identification of growth and dissolution of calcite crystals influenced by evaporation-condensation phenomena, as seen in decorated caves or shelters
Growth phase (polymorphism) (evaporatory conditions)
Dissolution phase (condensation conditions)
Figure 4
Diagram showing the evaporation-condensation phenomena in the case of an artificially covered archeological site. Analysis was carried out in May and June 1992.
Forming of craters or pits (craterization)
Ablations (tips of needles and microdroplets) Flaking
Swellings and loss of cohesion
Figure 5
Ground plan of the excavation: P. S. = higher floor; P. I. = lower floor; M1 and M2 = eroded historic walls; A = clays; G. S. = shingle. Map of the observed increase of the bleaching area (salts) at different periods of time: line 1 =
31 March 1993; line 2 = 1 June 1992; line 3 = 22 September 1992. Lines 1, 2, and 3 are the limits of the bleaching area.
Single (pinpointed), clusters, larger areas precipitates: amorphous
Simple, complex growth (chaotic, massive)
Needles grafted onto flat or “conchoidal” supports
Pointed budding disorganized, organized, thin layers, flakes
Processing of these data make it possible to follow the phenomena of crystal growth stage by stage.
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