In some cases they can literally crumble just sitting on the shelf. First indication may be slight irregularities to the surface that develop into bulges. Those bulges can eventually just fall off leaving a pile of "powder" at the pots base. Once it is visibly bulging it may take only the slightest contact to result in pile of powder left in your hands that loosely matches a concave void left in the side of the vessel. The main thing is though that if you have a stable controlled environment hopefully the condition is not really "active".