An-Najah Staff

Prolonged immersion in seawater results in chemical alteration of ceramics. This interaction primarily involves some earth alkalis. In the first experiment (six years duration), a powdered calcareous ceramic lost up to one-third of its calcium, gained an equivalent molar proportion of magnesium, and lost some of its strontium. XRD analyses showed it is free calcium phase (CaCO;, Ca (OH)= or CaO) that disappears, and that Mg= CO|(OH):'5H= O is formed. A second experiment, two months of contact with seawater for fired synthetic mixtures of ...

The identified pigments in Vallon roman wall painting are : egyptian blue, calcite, goethite, haematite, green earth (céladonite or glauconite) and soot or charcoal. Owing to the fire, these paintings suffered considerable damages : cracking and weakening of the plaster and of the paints and change of some colours. We observe the transition from white to grey, from yellow to red ; from red to a more or less yellowish brown or to black ; from green to grey, to red or to brown and the disappereance of the black paint. After burial in a clayey and wet soil, these paints show different types of alteration : a calcareous patina and a lot of black spots associated with different colours. These spots were found to be iron and manganese oxides, probably produced by bacterial activity. A preliminary chemical test carried out on some treated paint fragments has shown the presence of some traces of the used chemical products.

After treatment with milk, wine, urine and different phosphate solutions, all the studied ceramics have shown an important phosphorus uptake. The quantity of phosphorus fixed by ceramics depends on the interaction of ceramic characteristics (mineralogical nature, firing temperature, presence or not of calcite) with the pH and the phosphate concentration of burial or use media. The observed phosphorus uptake is best marked where clays are less fired, where they are calcareous, where the time of contact with the medium and its temperature increase. The optimal fixation occurs in slightly acidic medium, less acidic for the calcareous ceramics than for the non-calcareous ones.