moist
It is very important that the silencer has dried out properly before storage.
Water and moisture create a corrosive, white substance. To avoid this, the silencer needs to dry out properly. This is most easily done with compressed air, a heat gun, a hairdryer, a fan, or similar methods.
corrosion
Corrosion can manifest in various ways. The culprit in the drama is moisture that hasn't been properly dried.
Water and moisture combined with gunpowder residue contain ammonia and other corrosive substances. If the silencer is not properly dried and oiled regularly, damage can occur that affects performance. Read more about this in the "Maintenance" section.