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.