[Illustration: Fig. 9. Bronze Pasht showing destructive patina.]
[Illustration: Fig. 10. The same after treatment (Finkener's method).]
[Illustration: Fig. 11. Bronze Pasht showing destructive patina.]
[Illustration: Fig. 12. The same after treatment (Finkener's method[64]).]
Nor am I able to endorse the statement of Friedel[65] that a spreading patina is characterised by a peculiar and disagreeable smell, although some oxidized bronzes have a distinct smell which it is not easy to describe.
The presence of chlorine is particularly dangerous to those bronzes which consist of a casing of metal of variable thickness around a core of sandy clay, the object of which has been to economize metal. These constitute an important class amongst Egyptian bronzes. The chlorine often exists in the core as sodium chloride, and can thus attack the metal from both sides. Moreover, the structure of many Egyptian statuettes of a later period is very porous and spongy, and thus presents a large surface to destructive agencies. On sawing through the support of an Osiris[66] numerous small bright spots were found, upon examination with a lens, to be small pores filled with a salt solution. A few days later the action of the carbonic acid had begun, and the bright spots of moisture were represented by small green patches. The following figures show the absorption of moisture and of carbonic acid by this specimen and by another Osiris from the Egyptian collection.
Weight, air-dried 14·6554 gr. After one day in the desiccator 14·6514 gr. Air-dried, after one day 14·6540 gr. Air-dried, after ten days 14·6576 gr. Air-dried, after one month 14·6599 gr. Air-dried, after two months 14·6623 gr. Air-dried, after four months 14·7261 gr. After a prolonged period in the desiccator 14·7033 gr. Air-dried, after one day 14·7254 gr. Air-dried, after one month 14·7321 gr. Air-dried, after two months 14·7362 gr. Air-dried, after four months 14·7381 gr.
Weight, air-dried 77·7522 gr. After some time in the desiccator 77·7397 gr. Air-dried, after one day 77·7462 gr. Air-dried, after ten days 77·7548 gr. Air-dried, after one month 77·7582 gr. Air-dried, after two months 77·7617 gr. Air-dried, after four months 77·7704 gr. After being heated to 200°C. in the drying stove and lying one day in the desiccator 77·5967 gr. Air-dried, after one day 77·6752 gr. Air-dried, after one month 77·8044 gr. Air-dried, after two months 77·8191 gr. Air-dried, after four months 77·8320 gr. Air-dried, after seven months 77·8444 gr. After four days in the desiccator 77·8225 gr.