Cancellation

Cancellation is the term for removing magic from an object or disabling the special attack of a monster. The most common source of cancellation is the wand of cancellation. A few are able to use the spellbook of cancellation. Those wielding Magicbane can sometimes cancel monsters that way. Foocubi can spontaneously become cancelled.

Cancellation of objects
Cancellation typically removes all charges from an object, removes enchantment (resetting weapons and armor to +0), and removes blessings and cursings. Scrolls and spellbooks are blanked, and most potions are converted to uncursed water (booze, fruit juice and oil are just made uncursed, while see invisible and sickness become uncursed fruit juice). In short, cancellation is quite thorough. However, cancelling a bag of holding does not turn it into a sack and has no effect whatsoever on the contents. Similarly, cancelling a magic lamp uncurses it but does not turn it into an oil lamp. Irina Rempt has written an excellent spoiler on cancelling objects.

Canceled wands cannot be recharged. (This fixes a bug that had allowed players to gain infinite wishes by cancelling their wand of wishing.)

Cancellation of monsters
Cancelling monsters eliminates most forms of attack they have (except inflicting physical damage). In particular, cancelled monsters cannot blind with light, cast spells, charm, confuse, disenchant, divide, drain stats, explode, heal, mimic, paralyse, prick, poison, put to sleep, rust, rot, seduce, slime, spit, steal items (except the Wizard of Yendor) and intrinsics, stick, stun, summon, teleport, wrap around or use any breath weapon, cold, fire or electricity attack, whether as an offensive or defensive ability, with respect to you or any other monster.

Cancelling clay golems causes them to be destroyed immediately (this is because they, according to legend, are animated by an inscription on their forehead, which the wand erases).

Cancelling Medusa removes its stoning gaze, which also means that it cannot be stoned with a reflecting item. Similarly, cancelling a floating eye means it cannot be paralyzed with the same.

Some attacks which are not magical in nature cannot be cancelled, these include:
 * the special attacks of the Riders (disease for Disease, hunger for Famine and touch of death for Death
 * the blinding attack of ravens
 * mind flayers brain attack
 * the attacks of the Oracle
 * defensive acid splashing

Breaking the wand
If you break a wand of cancellation, there is an explosion from 1 to (4*charges) damage. Monsters and objects in the affected squares are cancelled.

Considering when to cancel
Suppose you need some blank scrolls and spellbooks and some potions of water, because you plan to use your magic marker and make holy water. You have two choices; you could wet them or you could use cancellation.

If you can find a wand of cancellation, then a strategy is to initially use cancellation. This is because you can pile all your junk scrolls, spellbooks, and potions, then zap it with only one charge. However, once you acquire water walking, do start dipping things into a moat. (Remember to kill the ;| first!)

The advantage of this strategy is that you do not need to use fountains, whether you already dried every fountain or you just want to avoid the nasty side effects. When you switch to the moat, you can save cancellation for use against monsters, and you can also dilute your potions of fruit juice.