It can be performed by mechanical means, as in dye penetrant
technique, with the disadvantage of being intrusive and may lead
to the removal of bacterial cells from inside the defects. Ultra violet
(UV) bactericide radiation can also be used to destroy bacterial
cells in exposed regions, that is, in non defective zones (Fig. 2a),
without interacting with bacteria inside the defects. Varying the
angle of attack ( ) of incident light, from tangential to perpendi-
cular, the sensitivity of the technique can be improved. Another
possible stage variant consists on the deposition of an antibacterial
agent (Fig. 2b) on the surface destroying the bacteria in non-
defective areas and preserving those inside micro defects, such as
cracks. Therefore, the presence of live bacteria indicates existing
micro defects.