182 Chapter 7
Fracture occurs at the weakest joint of an object, which connects this type of
damage with the production process. The resistance to mechanical wear is a
function of the surface hardness; once scratches have occurred, they represent
prominent points for further attack.
3.7 Restoration and Conservation
Among all the materials used to create decorative arts, ceramics are the most
stable ones. Nevertheless, the damage phenomena described above occur on
ceramic objects; whereas some collections or groups of finds are more affected,
others are more stable, depending on the sensitivity of the objects and on the
damage potential of the previous exposure or storage conditions. More severe
problems occur if ceramics are combined with other materials, such as wood,
metals or organic materials within one object. Each of those cases requires
special consideration.
Storage conditions for ceramic objects should be optimised to minimise
furtherdecay. First of all, fluctuations of temperature and humidity should be
avoided to prevent salt crystallisation. Therefore, the general rule is to keep
objects in a dry environment, especially if retrieved from a dry exposure site.
Objects from damp environments might have to be kept wet, if an immediate
treatment is not possible. Removing damaging salts by long-term soaking in
water is a common method for future stabilisation of such materials. Air pol-
lutants increase the damage by chemical attack, especially on sensitive glazes
and should be therefore reduced in showcases and galleries. Extreme tempera-
ture changes and vibrations, causing thermal or mechanical shock, have to be
avoided. In contrast, light is an environmental parameter that does not play an
important role in ceramics degradation. Monitoring of light is necessaryonly
for very special coloured low-fired ceramics or to prevent degradation of
previously applied conservation materials.
Figure 17Glazed ceramic samples in the process of weathering: a non-weathered sample (left)
and proceeding damage on the glaze after accelerated weathering (middle and right)