Scroll of Identify

Permanently reveals all of the secrets of a single item.

Scrolls of Identify are rare when compared to the number of items that you will want to identify over the course of  a game. You will never have enough. These scrolls are best saved for use on whatever items will relieve you of the most frustration when compared to ID by use. Scrolls of identify are generated completely at random. In one seed you may find ten, in another you might find zero. Applying a potion of detect magic before you begin using your scrolls to identify your gear will make the scrolls last that much longer.

When you use a scroll to identify a wand, its type and number of charges will be revealed. This is often a good idea. Powerful wands like empowerment and domination can be potentially be rendered useless by expending its only charge use-IDing it. Just as bad, you might apply a very detrimental effect like invisibility or plenty on a dangerous monster, or polymorph on an inconsequential foe.

Equipping a cursed ring, depending on the type, has the possibility of ending your game rather quickly. Also, it takes 1500 turns to use-ID a ring. For these reasons, a ring is a good candidate for a scroll of identify, particularily if you have no means to determine its blessed/cursed status and/or have no means of removing a curse. 

If you use a scroll to identify a staff, its current number of charges will be known throughout the rest of the game. This is very useful for a wizard build or any character that relies heavily on a staff. In fact, it's so important that many experienced Rogues will use a scroll of identify on a staff even after its type and max charges have been learned, because having a staff fail you when you need it most is a fine recipe for Yet Another Stupid Death.

Whether or not to use a scroll of identify on a weapon is a mixed bag. Killing 20 enemies with an unknown weapon will identify it. This isn't much of a problem early in the dungeon, but as you move deeper, enemies become more dangerous and you typically get more creative. If you kill 20 enemies with a weapon and it is identified as having an unknown runic, it may be worth spending a scroll to find out which runic it has.

It takes 1000 turns to identify armour rather than use a scroll on it. This usually isn't too much of an imposition. As with weapons, if after 1000 turns you find it has an unknown runic, then you may want to burn a scroll on it.

It is very rare that you will want to use this scroll on a potion or another scroll. Sometimes, once you have narrowed down possibilities far enough, it might be worthwhile.