This operation consists of passing the filled cans through a bath (or a shower) of hot water with various additives. It can be aggressive for the ink film when not varnished. A discoloration of the controlled cans during this test can be considered as fault.
Low over varnish film weight.
Increase over varnish film weight.
Over varnish separated into two phases.
Properly agitate the over varnish container.
Varnish applicator is not adjusted.
Check for varnish voids.
Some inks are not suitable.
Follow the TDS series from the ink supplier.