In addition to the chlorine compounds, there was also a considerable quantity of sulphates, the presence and disappearance of which were tested by adding to a few cubic centimetres of the water a dilute solution of barium nitrate or of barium chloride[100]. The soluble barium salts give with sulphates a white precipitate or cloudiness of insoluble barium sulphate. If therefore on the addition of a solution of barium nitrate no cloudiness appears, even after some time, it may be concluded that sulphates are no longer present in the water. When the ostraca have been washed and dried, it is often possible to make the script more distinct by varnishing them over with a varnish-benzine mixture (1:6).
It is advisable to subject friable objects of earthenware to the process of impregnation (cp. the impregnation of unbaked clay, p. [81]).
The Removal of Incrustations. Incrustations of earth or lime can be easily removed if the earthenware has been well baked, but trial must first be made with a drop of dilute hydrochloric acid, whether the earthenware itself is not attacked by the acid. The specimen is then placed upon a glass ring or suspended in water containing 2% of hydrochloric acid[ [101]. This mixture, which must be renewed every 24 hours, will remove incrustations which it would be difficult to remove by mechanical means, while crystals of gypsum of considerable size, which are often found on clay tablets of Assyrian origin, are easily dissolved in from two to four days.
Figures [16] to [21] represent two Assyrian tablets which have been cleaned by myself in this manner. It will be seen that the cuneiform characters, which before treatment were almost invisible, are now distinctly legible.
Fig. 16. and Fig. 17.
Assyrian clay tablet with incrustations. Before and after treatment.
Fig. 18., Fig. 19., Fig. 20. and Fig. 21.
Assyrian clay tablet before and after treatment.