The crystallization process of soluble salts inside the natural and artificial porous materials partially immersed in different saline solutions has been studied, This procedure is used to simulate the conditions of exposure to salt weathering in which foundations and lower walls of building structures are within the zone of capillary rise of saline ground water.Crystallization pressures that can develop in the samples, which are a function of the pore size and salt-solution interfacial tension, have been calculated and are compared with experimental values of the materials tensile strength. since both these parameters allow the prediction of porous materials behaviour against salt weathering.

In order to study the processes of salt weathering of monumental stones, several samples were partially immersed in sodium, potassium and magnesium sulphate solutions which ascended through their capillary network and, eventually, crystallized. This procedure pretends to simulate the conditions in which foundations and lower walls of building structures are, within the zone of capillary rise of saline groundwater. Mass transport and the rhythmic nature of crystallization fronts inside samples reminds the Liesegang phenomenon, so they have been considered as a form of dissipative structures. The saline deposits developed on the surface of the samples were effiorescences (mirabilite and epsomite), subeffiorescences (picromerite, aphthitalite and arcanite) and crusts (aphthitalite and arcanite). The most devastating effects resulted from massive crystallization inside the samples or from surface peeling due to the develop ment of subeffiorescences or crusts.

Supersaturation evaluation is an essential requirement to describe, confront and explain crystal growth experiences. However, in the particular case of crystal growth in gels, experiences are often described by attending to the initial concentration of reagents. This fact is wnnected with deficiencies in the theoretical quantification of mass-transfer, and therefore in both time and location prediction for the first precibitate. In this paper laboratory experiences have been specifically designed to test supersaturation evolution through an actual (finite) diffusion system. The problem is carried out by keeping into account several complexity factors: free ions as well as complexes and silica gel Na+ and C1-"unloading" are considered to evaluate the supersaturation.

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This paper highlights the contribution of transmission electron microscopy (TEM) when combined with scanning electron microscopy and energy-dispersive X-ray microanalysis (SEM/XEDS) to characterize objects in archaeology. The application of TEM in archaeology is not yet a common tool, but it may provide data that are significant to understanding pre-Columbian gold metallurgy, specifically the gilding and silvering methods. Two gilded rods were studied using a combination of TEM and SEM/XEDS techniques. The objects were found at the Atacames archaeological site, in the Esmeraldas region, Ecuador, which was occupied between AD 750 and 1526 by the Atacames culture. The microchemical and structural results of the inner and the external gilded part of the artefacts support the hypothesis of a gold diffusion to the surface enhanced by chemical treatment with chloride-rich solutions, heating and successive annealing processes. The present study reveals that microstructural investigation by TEM provides useful information with which to investigate the techniques used to modify the chemical surface composition of pre-Columbian artefacts.