Suppression is a status effect which causes all magic items to behave as their mundane counterparts. Magical staves act as nonmagical lengths of wood; magical swords act as nonmagical (but sharp!) hunks of metal; magical armors act as nonmagical strips of leather and hide.
Suppression blocks all worn and wielded magical item properties (resists, brands, etc.), as well as the evocation of magical items (rods, wands, jewelery, miscellaneous items). The base properties of weapons and armor (damage, AC, enchantment bonuses.) are unaffected. While it may seem as though this has some uses, curses are kept, and the negative effects that occur when certain items are equipped/unequipped (vampiric, distortion) happen as usual.