If the coating is porous at the start of the measurement than the
can is excluded (see Section 3.1); only “good” cans are used for this
measurement. However, the inside coating can have weaknesses
at many different locations, like blisters, very small scratches, dust
particles, too low thickness, etc. These weaknesses might not show
as a pore at the start, but might grow into an increasingly larger
pore in time.