HTML Conversion by Kate Nepveu
Version 1.4.3 - all versions 1.4.* are for NetHack 3.4.3
First 2006 Edition
This spoiler details techniques for identifying objects in the face of a shortage of identify scrolls; it's actually possible to sort out nearly every object in the game without risk of adverse consequences. I am keen to have submissions on additional methods of identifying objects, or corrections to any errors in this spoiler. I am not keen to be told that I use British English spellings; you wouldn't think I'd have to mention that, but unfortunately that is not the case. I deal only with vanilla NetHack, but the techniques will be useful in variants.
This spoiler is really long; you have been warned. You may freely distribute and modify this spoiler under the terms of the GNU General Public License - version 2 of the License, or at your option any later version. It is by no means all my own work; I must acknowledge assistance (in no particular order) from Dylan O'Donnell, Klaus Kassner, David Goldfarb, Raisse, Zack Weinberg, Kathrin Paschen, Michael Hedera, Eva Myers, Rob Elwood, Kate Nepveu, Marisa Lohr, Gregory Bond, Chris, Jaakko Salomaa, Kieron Dunbar, Dan Sheppard, Tina Hall, George Fleming, Ian Jackson, Lotta Loytonen, Topi Linkala, Jukka Lahtinen, David Throop, Keith Hearn, Trebor Rude, Colin Watson, Seraphim, Wes Irby, Jakob Creutzig, Patrick Clot, Shawn M. Moore, Martin, Doug Freyburger, Rast, Michal Brzozowski, kb, Matt Rei, Stephen Oberholtzer, Peter Maydell, some mystery contributors, and no doubt one or two I've forgotten (sorry).
If you do have some identify scrolls, you should always bless them and ensure you have as many unidentified objects in your inventory as possible before reading them; there is a one in five chance that a blessed scroll will identify everything in your main inventory.
It is vital that you understand the use of the #name command; either to name a specific object (this particular potion is uncursed) or a class of objects (these scrolls cost 50 zorkmids in shops.) #name is also useful to sort out objects with identical appearances; if you #name the first kind of lamp you find 'lamp 1' and then find an unnamed lamp, you know one of the two kinds is magic, or if you #name a red gem 'red gem 1' and find an unnamed red gem, they can't both be worthless glass. Where the object has not been completely IDed it is best to include the appearance in the name; for example, if a scroll type is named "READ ME costs 100" it can be distinguished from a second scroll type named "YLOH costs 100", or if a wand is named "uranium vanisher" it can be distinguished from a second wand named "iron vanisher". It's worth noting that you can blot out an existing name by #naming the object with just a single space character - this is extremely important because when you have a vague name for an object (like "orange costs 100") and want to actually try one out, you'll only get the 'call' prompt if it's unnamed; and that when the game asks a question like "Call an orange potion?" that's equivalent to #naming it.
A pleasantly cheap trick with #name is that you cannot name an individual object (answer 'y' to "Name an individual object?") after an artifact if the object is of the base class of that artifact; "While engraving your hand slips". This is useful in three cases; you can't name a gray stone "The Heart of Ahriman" if it is a luckstone, you can't name a helmet "The Mitre of Holiness" if it is a helm of brilliance, and you can't name an amulet "The Eye of the Aethiopica" if it is an amulet of ESP. Hence you can, for example, try so #name-ing every amulet you find - if your hand slips, you know you have ESP. There is a certain amount of controversy over whether this is outright bug abuse.
An awareness of item probabilities helps; if you find six of 'lamp 1' and one of 'lamp 2', it's not hard to guess which is magic. Also, if you know all but one items in a given category (such as scrolls, potions, or amulets), the last one can be determined by elimination (eg, "I've IDed every scroll except genocide, and I have this one marked ELBIB YLOH.")
A lot of techniques demand that you know the blessed/uncursed/cursed (henceforth "b/u/c") status of an object, or at any rate that it's not cursed. Dropping items on altars works (or being a Priest), but your pet will not walk on a cursed object (unless you displace it, there's food there, or it "moves only reluctantly"); if you leave your pet behind, I've no sympathy. Watching monsters use weapons and take off armour is also instructive; cursed wielded weapons are noticed as such (if you see the monster actually wield it or fail to unwield it), any item (including potions) that 'slips' or 'misfires' as a monster throws or fires it is cursed (but a cursed item will not always slip), and any armour a monster removes is not cursed (but there are no visible effects from them failing to do so.)
Some objects are always generated uncursed (otherwise, objects are usually uncursed, but sometimes blessed or cursed with roughly equal probability, unless noted otherwise): non-tin food; gems other than loadstones; tools other than light sources, grease, crystal balls and figurines; armour and weapons with positive enchantments (may be blessed); statues and boulders. But beware bones piles, where all bets are off. There are also some mentions of messages from cursed items, in case you really do have no way of determining b/u/c status.
Some objects give you the message "You have a strange feeling for a moment, then it passes" if flags.beginner is set; roughly speaking, this is the case if you have never had more than 500 XP (250 for wizards). If you don't have showexp on, a level 6 Wizard or a level 7 anything qualifies, provided you have not gained XP from potions of gain level, wraith corpses, or sex (which don't count). This is important because you cannot always distinguish objects when this happens.
Some objects can be identified if you zap a wand (or drink a potion) of enlightenment while wearing/carrying them, but the possibilities there are too great to number - for instance, one can distinguish flint stones and luckstones, but this technique is most useful on uncursed rings and amulets. The Monk Quest Artifact, the Eyes of the Overworld, can be #invoked for enlightenment - an unlimited supply.
Various races and classes begin already knowing certain objects - mundane weapons and armour for combat wombats, your racial gear if non-human (only really useful for elven boots) - and, of course, you always have your starting inventory identified.
There are some guaranteed objects at various points in the dungeon. Primary amongst these are the gem piles in the Gnomish Mines and in Fort Ludios (see 'Gems' below); the 'statue of a knight named Perseus' on the Medusa's level, which may contain a cursed shield of reflection, levitation boots, a blessed +2 scimitar, and/or a sack; the top level of Sokoban contains either an amulet of reflection or a bag of holding (on the space marked "Elbereth"), and the two scrolls found in the bottom left corner of the bottom level are always scrolls of earth; Vlad's Tower contains an amulet of life saving, amulet of strangulation, water walking boots, crystal plate mail, and a spellbook of invisibility on the middle level, and a long sword, lock pick, elven cloak and blindfold on the bottom level; Orcus always carries a wand of death; and the Wizard will bring a spellbook of dig to the Plane of Earth.
The most basic technique for a lot of classes of objects is grouping by price in shops. Everyone knows that identify scrolls are the cheapest (don't they?); but a lot of other objects can be reduced to two or three possibilities by price grouping. This technique is useful for things like potions and scrolls, where you want to know (say) what scrolls marked ELAM EBOW are; less useful for things like weapons where you know what long swords are but you want to know what this particular long sword is. Hence, I'm going to open with a discussion of how the sale or purchase price of an object is determined from the base price - the cost listed in objects.c. You may also want to examine the 'shopping' spoiler.
For most objects, the price is the base price multiplied by a few fiddle factors for things like Charisma. First, though, the base price is hacked about for a few things. If you're hungry, food is much more expensive (but you don't need to price group food items.) An empty unrechargeable (possibly cancelled) wand is worthless (but if you're buying, the base price of a 'worthless' object is 5 zorkmids); so is an uncursed potion of water (always a 'clear potion', so easy to identify.) The base price of armour and weapons is increased by ten zorkmids for every point of positive enchantment. Used candles are worth less, but identifying candles isn't really important. Unidentified gems are cheap if selling or pricey if buying; the details have been relegated to the gems section.
If you're buying, one in four objects (based on the object ID number, so consistently for a given object) has its price increased by a third. This is awkward and nearly unavoidable, especially if it prevents you distinguishing an object with a base price of (say) 60 from one with a base price of 80. Where base prices are so positioned, you may need to see several objects of a given type before you can determine what's really going on; since this is the only surcharge that's unpredictable and applies to some but not all objects of a given type, references to being fooled by the surcharge refer to this one.
If there is a second object of the same type in the shop, but only one is surcharged, and they stack, I am told you can get both at the lower price by dropping the cheap one on the expensive one and picking them up again, not that this really pertains to identification. For identification purposes you will of course want to price each item in a stack individually.
A dunce cap, a visible shirt (no body armour or cloak) or being a tourist of level 14 or less carries a surcharge of another third, as does an angry shopkeeper (but then you may be more concerned with not dying.)
Now we've got all these avoidable things out the way, there's an adjustment for Charisma; Cha below 6 doubles the price, 6-7 adds one-half, 8-10 adds one-third, 16-17 subtracts one-fourth, 18 one-third, and 19+ subtracts one-half.
If you're selling, the base price is first of all divided by two - three if you're a low-level tourist, wearing a visible shirt or a dunce. 1/4 of sales (at random) have the price reduced by 1/4, but (unlike the random purchase surcharge) you can circumvent this by getting 2-3 quotes on the same object. Sale prices are also not influenced by Charisma, making identification of an object's price group much easier when selling - of course, if you can afford to buy an object, you can do so and get a sale quote immediately afterwards; and if you don't have an object of your own to get sale quotes on, IDing is of less interest (although you might find one later, obviously, and want to use it without returning to the shop; or simply be planning to rob the shop in a way that angers the shopkeeper).
A shopkeeper who has insufficient cash will offer 'only n gold pieces' for an object (where 'n' is all the gold he has); clearly this limits the deduction possible about the sale price. However, a shopkeeper with no gold at all will offer credit equal to 90% of the sale price (as ever, the surcharge may apply), which is just as good.
It is worth noting that throwing an object into a shop makes it the shopkeeper's (as does killing a monster that drops it, greasy fingers, etc.), and even if the object is not one normally sold in that shop, you can now get a purchase quote for it. Of course, this is expensive.
Here's a table of some common base prices and the effective purchase prices. There are two rows of Charisma scores; one for prices where no surcharge applies and one for a price with one surcharge; you then find two prices below, one surcharged and one not. Why like that? So you can locate your Charisma score (in the second row, if you have an unavoidable surcharge) and simply look down the two columns to find all possible prices. Sale prices are equal to the purchase prices for a Cha 19+ with no surcharge. There are probably some rounding errors; sorry.
|Cha (no surcharge)||3-5||6-7||8-10||11-15||16-17||18||19+ or sale||19+|
|Base Price (down)||Cha (with sur)||3-5||6-7||8-10||11-15||16-17||18||19+|
If you actually sell various mundane armours and weapons, the shopkeeper will identify them for you. This is only really useful for helmets and gloves, as noted in the Armour section.
A full discussion of this is beyond the scope of this document, but when you find a bones pile, you can have a very good idea of what some of the items in it are, especially if the dead character was not far advanced. A wizard corpse with a magical cloak is very likely the wizard's original cloak of magic resistance; a valkyrie corpse's small shield is probably +3; an archaeologist with a single grey stone probably had a touchstone, etc. However, this is by nature a gamble; never underestimate the perversity of your fellow players.
Now, onto some sorts of objects;
Potions can be identified in several ways, not least because monsters tend to use them; once you have somehow found some of the more harmful ones, you can just drink the (non-cursed) things, especially if you have a unicorn horn available and/or have done some price grouping - but even without price grouping you can probably start quaffing eventually.
Clear potions are water, but you knew that, right? No other potions have a fixed description, but using the (a)pply command will only present potions of oil as potential targets for the command, so they can also be easily identified.
The special functions of smoky and milky potions (djinn and ghosts) are not related to what type they are, but it is worth saving and blessing smoky potions regardless of whether they are a type you would normally drink.
Dipping a consumable missile weapon (arrow, crossbow bolt, dart, shuriken, but not daggers) into a potion of sickness will poison it (and now you know what the potion is; it 'forms a coating' on the weapon). Dipping almost anything into polymorph polymorphs it (see below). It's a smart plan to test potions that might be polymorph with a missile weapon, unless you have a spare unicorn horn; and it's a cheap way to ID sickness before you have a unicorn horn at all. Don't #name them before making this test; polymorph IDs itself, and sickness will prompt for a name. Dipping poisoned weapons into potions of healing (including extra or full healing) unpoisons them.
Dipping into polymorph is resisted ("Nothing happens.") by wands and spellbook of polymorph, iron balls attached to you, and armour merged with your skin; by artifacts 95% of the time; and by all objects 5% of the time. However, I do not believe that any other type of potions being dipped into can produce "Nothing happens" under any circumstances. If an object polymorphs into the same object again, you will be told "Nothing seems to happen".
If you have a unicorn horn, #dipping it into potions of hallucination, blindness or confusion will turn them to water, and turn potions of sickness to fruit juice (which is one way to distinguish fruit juice and see invisible.) Unless you want to keep potions of confusion for use before you wear out a spell, this is a very valuable tactic; #name all potions 'harmful <colour>' and dip a unicorn horn into them; if they don't clear or go a new colour, #name them back (if they go a new colour, #name them 'fruit juice', obviously.) The gotcha here is that you can't identify paralysis or sleeping like this, so you can't get rid of all massively harmful potions; however, Eva Myers points out (amongst other things) that a ring of free action negates the harmful effects of either, but they are still identified.
If you have an amethyst (easy to find if an archaeologist, or if you have three violet gems with different #names - one is worthless, one is fluorite, one is amethyst), it will turn booze into fruit juice.
Monsters may drink the following types of potions; healing, extra healing, full healing, gain level, invisibility, speed, polymorph. Pestilence may drink potions of sickness, but that's kind of obscure. Nearly all these cases identify the potion for you; the only exception is cursed gain level ("<monster> rises up, through the ceiling!"), where you are called upon to supply a name.
Monsters also throw paralysis, blindness, confusion, sleeping and acid. Paralysis, sleeping and blindness identify themselves; confusion ("You feel somewhat dizzy.") and acid ("This burns!") ask you to supply a name. There are some cases where a monster might throw a potion that hits another monster; my reading of the source is that you are not called upon to supply a name (unless you breathe the vapour), but if you can guess it right and have another sample in your inventory you could #name that (even if you can't guess, it must be one of those five, so can be #named "thrower" or whatever.)
In theory you could go chucking unided potions at monsters to see what they do, but that is normally pretty daft (or dangerous, in some cases, especially polymorph.)
There are guaranteed to be six potions of booze in the Gnome King's Wine Cellar, so if you get that mine ending you can effectively eliminate booze from consideration; also the southernmost pile will contain a potion of object detection (and only that), which is handy if you haven't killed a lot of nymphs yet. (The Gems section discusses which mine ending is which, but providing layouts is beyond the scope of this spoiler). There is always an amethyst in any mine ending, so a little work with violet gems lets you write off fruit juice, too.
Nymphs often (one in two) have potions of object detection, but they also can have other random potions. Shopkeepers often have healing and extra healing (in their own inventories, not their shops.)
A delicatessen stocks and buys only potions of fruit juice, booze, and water (but, like any shop, will sell any item that happens to land in it - thrown in, dropped by a dying monster, or whatever.)
If you have the input to an alchemy recipe, you could identify the output potion by carrying it out and seeing what appearance the result has. You would need to refer to the alchemy spoiler for a list of all possible combinations.
Now, by price group;
5 - uncursed water. It's clear, anyway, but this lets you know which of your potions of water are uncursed. If you really have no altars, you can sort your potions of water into three groups (which will refuse to merge in inventory); having eliminated uncursed by price or probabilities, you can dip a useless object (or see below) into one of the other two stacks and see what happens to it, to determine which stack is holy water. This makes it more practical to head for Sokoban before Mine Town.
It's best to dip a cursed useful object if you have one. If you picked unholy water, nothing happens ("Interesting..."); if you picked holy water, you were going to use it up uncursing that object anyway. Hence, you avoid a wasted potion.
50 - see invisible, booze, sickness, fruit juice.
The presence of sickness in this one is a bit of a nuisance, since monsters won't identify it for you, but testing with missile weapons makes it easy enough to sort out. Blessed sickness does nothing, so blessed potions in this group are safe; healers are immune in any case; if the damage won't kill you, a ring of sustain ability will prevent the stat loss, or you might know and have a stock of restore ability - or you might have started with a potion of sickness.
See invisible and fruit juice both "taste like fruit juice". Non-cursed see invisible (but not fruit juice) will unblind you if you are blind, which may help to pick them apart; also, fruit juice adds a modest amount of nutrition (between 5 and 30 based on blessing and dilution); hence you can distinguish fruit juice from see invisible by drinking one when you have just crossed a hunger status boundary (eg, just become Hungry).
If the potion is cursed, fruit juice and see invisible both say "Yech! This tastes rotten." Booze makes you pass out; sickness does more damage.
Note, above, that a deli helps you sort this lot out - not just by what it sells, but by what it buys.
If you can already see invisible, all potions in this group are basically useless. Sometimes it's not worth the bother.
100 - restore ability, confusion, hallucination, healing, extra healing, sleeping, blessed/cursed water.
Sleeping and confusion are quite irritating, but can usually be safely drunk in a locked room. Hallucination is the real stinker here, without a unicorn horn - also, the monsters won't sort that one out for you. Whether it's worth going through all that to find restore ability by elimination is up to you, but if you're really hurting for it, go ahead. Restore ability, which does not auto-ID, will make you feel 'great', 'good', or 'mediocre', but never 'tastes' of anything.
150 - blindness, invisibility, monster detection, object detection, gain energy.
Once you've had blindness thrown at you or unicorn-horned it out or have a means of curing it (and have a mummy wrapping, if planning to shop), go ahead with this group, if uncursed. Cursed invisibility gives you aggravate monster - also, you can't identify it if you're already invisible, so you may need to see a monster drink it.
Monster detection; it's wise to check there's a monster around if flags.beginner is set, since otherwise you won't ID it for sure; if you're not a beginner, "You feel threatened." (or "You feel lonely", if blessed).
Cursed gain energy makes you feel "lackluster", but is still identified.
Also, annoyingly, if you get surcharged buying these potions, they look like the ones in the next group.
200 - speed, levitation, enlightenment, full healing, polymorph.
Without polycontrol polymorph is likely to make your life miserable regardless of b/u/c status. If you must try potions in this group, do it without shirts, body armour or cloaks in a locked room, on a level with a sink (which eases the effects of unblessed levitation; cursed levitation causes you to hit your head on the ceiling but is no worse than uncursed thereafter). Enlightenment and full healing can be identified even if cursed (enlightenment makes you feel "uneasy"); speed will normally be identified for you, but a non-cursed speed will heal wounded legs and need to be #named 'speed', or if you are already very fast your legs will 'get new energy' (but no auto-ID.)
250 - acid, oil.
Since you can use the (a)pply trick to identify oil, weeding out acid is also trivial once you can price-ID. Acid "explodes" when immersed in a pool or moat, but since this would possibly destroy other potions this is only useful after an accident, if you can remember what you had beforehand...
300 - gain ability, paralysis, gain level.
This group's quite tricky, and often better left. Gain ability is a bit wasted if not blessed ("tastes foul", if cursed); gain level is wasted at low levels, or if cursed, or if unblessed at intermediate levels; and paralysis is nasty, blessed or cursed. Once you've got paralysis out the way (by having it thrown at you?), it's probably worth hanging onto the others to bless them.
Scrolls are trickier than potions; monsters don't use so many of them, and amnesia will always ruin your day, so there's nothing much to be done but identify scrolls that might be amnesia. Sufficiently lucky wizards with magic markers and a stock of blanks can always try writing the scrolls they are most worried about (as can any class, but with only a 1/3 chance with maximised Luck, so you'd need a large surplus of marker charges for this to be sensible).
A scroll by itself in a one-space corridor 'closet' in the wall is practically always teleportation (and, if there are multiple scrolls, one of them is practically always teleportation), as is a scroll in a corridor next to a room in general.
Like clear potions, an unlabelled scroll is always blank, but can be read (and not consumed) to identify it. But who cares?
Monsters may use scrolls of teleportation, create monster, and earth, but earth is quite unlikely.
Conversely, the fact that many scrolls have different effects while confused can let you weed out some of the harmful ones relatively unscathed.
The fact that scrolls of scare monster will crumble to dust if picked up often enough makes them easy to spot - but if you are in a shop and you are really broke, you may want to take care to get scroll prices via #chat.
As mentioned earlier, there are always two scrolls of earth on adjacent squares in the lower left corner of the first level of Sokoban.
You can try writing unknown scrolls with a magic marker. The odds are greatly improved by being a wizard and/or having maxed Luck, to the point that this is quite viable for a very Lucky wizard. They are not auto-IDed when you succeed, but you of course know what they are.
Now, by price group;
0 - mail.
20 - identify.
This one is easy; it's also very common - with twice the item probability of the next most common scroll, although the various special cases that create teleportation probably mean it is created still more frequently. If you really don't have any suitable shops, accumulating a vast mass of scrolls and reading the common ones may be the only thing to do.
50 - light.
Also unique in cost and auto-identifying when read; but, unlike identify, largely useless and a prime candidate for blanking.
60 - enchant weapon, blank.
This group would be easy if a surcharge didn't make it look like one of the next group. If you don't know the b/u/c status, you could get confused and read it while using unrustproof (or fireproof) weapon and armour; cursed confused enchant weapon removes rustproofing, but there will be none to remove. However, if it's blessed remove curse it'll still ruin your day. Another approach would be to try unconfused with expendable armour and weapon - if you can uncurse things affected by remove curse.
80 - enchant armour, remove curse.
These are not so easy unless you know the b/u/c status, because a confused remove curse randomly curses or blesses some of the objects it would otherwise have operated on. Oddly enough, that means (if you are wearing no rustproof armour) that cursed confused is safe; remove curse just "disintegrates".
100 - destroy armour, confuse monster, scare monster, teleportation, gold detection, food detection, magic mapping, fire.
The presence of fire and destroy armour in this group make it harder than it might be. If you're fire resistant or can take the damage and don't have any flammable objects, fire's OK; destroy armour can be handled by not wearing any armour (but you get a "strange feeling" instead of "Your skin itches." if flags.beginner is set) or by wearing a piece of junk (but uncursed) armour. These two are more easily mitigated by being confused (fire sets light to your hand, destroy armour makes a piece of armour glow purple and potentially changes its rustproofing status), but the effects of some of the others are more severe if you are confused.
Confuse monster confuses you if cursed; if you are confused, it un-confuses you if blessed ("a red glow surrounds your head"), or makes you more confused. Scare monster gives you "sad wailing" or "maniacal laughter" (but, if cursed or confused, attracts monsters). Teleportation will level teleport you if cursed or confused (eep!). Gold detection detects traps if confused or cursed - looking like gold, if cursed. Confused or cursed food detection detects potions; the best way to handle this one is to ensure there are some food items (and a potion, if it's not known uncursed) around to be detected.
I think the best way to handle scrolls in this group is to eliminate teleportation and then read them while confused and wearing no rustproof armour. Failing that, wearing junk armour and having no other inflammable items around may do the trick; but teleportation can still blast you across the level (into a sticky situation, naked.)
200 - create monster, taming, amnesia, earth.
Amnesia must be identified somehow, making scrolls in this group a prime candidate for whatever identifies you do have - but note, above, that one can identify earth from Sokoban. Assuming that's been done, earth does nothing in the endgame (other than on the plane of Earth) or on the Rogue level, but creates at least one boulder anywhere else regardless of b/u/c; if confused it creates rocks in the pattern of boulders you would otherwise have gotten. If you aren't equipped to deal with a potentially large number of monsters, confused create monster creates acid blobs, which also guarantees you will be able to see the results and so know what you got. That leaves taming as the one that might do nothing visible (but then you know what it is, anyway); interestingly, the effects of taming cover a much wider area if confused. Wasting a scroll of taming is irritating, but you have a 50% chance of identifying it before amnesia anyway.
300 - genocide, punishment, charging, stinking cloud.
Stinking cloud pays no attention to confusion, and always identifies itself. Beware that the cloud's radius may be as large as 4, if blessed; don't poison yourself.
Uncursed confused genocide will kill you very dead indeed. Cursed confused genocide sends in 4-6 of your own role, which can be nasty. Blessed confused genocide functions normally, which means you can do confused testing of this group if you know the scroll is blessed (but then you might as well just use it while unconfused.)
Punishment is easy; if confused or blessed, "You feel guilty.", and if you have a pickaxe or a pit to hand and a boulder, you can ditch the iron ball in no time (arrange to push the boulder into the pit while the ball is in it.)
Charging makes "You feel charged up!" if confused (increasing your Pw), but otherwise identifies itself.
I'm inclined to feel scrolls in this category are usually best saved; a spare blessed charging spares you a wish on your first WoW, and genocide is best used in pant-browning emergencies. Bless 'em and save 'em; when you find that WoW, you can always wipe out liches if you happen to read genocide first.
The traditional method for identifying most wands is to engrave with them after first writing something else with your fingers in the dust; by and large, this either identifies the wand or gives a message you can use to identify the wand. However, four wands give no result; one group of three and one of two give identical messages; and, if wands are found in a shop, you will be charged usage fees for the charges you consume. It is worth wearing unidentified objects such as rings, special armour, and amulets that are known to be safe if the wand you are engrave-testing might be enlightenment.
See also the spoiler at <http://www.steelypips.org/nethack/wand_id.html>.
Light, enlightenment, create monster, digging, fire, lightning and wishing will identify themselves immediately, as will secret door detection if by some chance there is a secret door in the room. Lightning blinds you if you engrave text, but not if you hit Enter when asked for a direction. The following wands give unique messages;
The following wands give no message; Nothing, undead turning, opening, locking, probing, secret door detection (normally). If you can be bothered, you can line up a locked door/chest, an unlocked door/chest, a corpse, and a live monster; all these wands do something to that lot, except nothing and secret door detection; and nothing prompts for a direction where secret door detection does not.
Death and sleep both give "The bugs on the floor stop moving!"; find some nice monster to volunteer for testing purposes (beware bounces). The odds are ten to one that it's sleep (unless Orcus dropped it).
Make invisible, teleportation and cancellation all cause the previous engraving to vanish (actually, a teleported engraving is elsewhere on the level, so if you find it you know which wand you had), which is a bit awkward, especially as you can hardly zap them at yourself.
Lining up a monster and a junk object does for this; if both vanish, it's teleportation; if the monster vanishes, it's make invisible. Alternatively, you can use a slow-moving monster, since you can just nip across to its space and try to smack it if it disappears - resist the urge to use a cancellable monster such as a floating eye, because it may make its magic resistance saving throw. A third approach is to use an object that changes with cancellation - if it goes away you had teleport, if it changes you cancelled it, and otherwise you had make invisible. A fourth technique is to stuff the wand into a spare bag of holding and see if it explodes - although personally I find it hard to envisage a situation where one would be that desperate to identify teleportation.
Price groups are included mostly for their utility when shopping, and also because you can sort out some of the previous differences with prices.
100 - light, nothing.
This lets you eliminate the wand of nothing from those others that do nothing when engraved with (but the rest of them all cost the same.)
150 - secret door detection, enlightenment, striking, make invisible, slow monster, speed monster, undead turning, opening, locking, probing, digging, magic missile.
There's a lot of wands in this group, and to make it more irritating the 1/3 surcharge can confuse them with wands in the next group but one; and you obtain wands so rarely that it's unlikely you'll have more than one to try. However, you can pick one of the 'engraving vanishes' wands out by price; make invisible.
175 - fire, cold, sleep, lightning.
These wands are a good choice when shopping, because they are readily identified, relatively inexpensive, and all deal effectively with monsters.
200 - create monster, polymorph, cancellation, teleportation.
Here's the other two 'vanishers'.
500 - wishing, death.
If you find one of these wands in a shop, you can line up the shopkeeper (but not yourself on the rebound) and attempt to let them have it. If it's death, fine; if it's wishing, wish for 2 blessed scrolls of charging and a wand of death, and let them have it anyway. If you're not concerned about killing shopkeepers, this is no bad plan, and it gives you about a 50% chance of netting a wand of wishing. Obviously if you can steal from shops effectively, you don't have to jump through these hoops.
Rings are difficult, because monsters never use them. Conversely, you can always try on a non-cursed ring for one turn and see if anything happens; the odds of (say) polymorph kicking in during that one turn are very small. Don't try this next to a powerful friendly (shopkeeper, say?) that will whip the snot out of you if it's conflict; do try it next to a wussy peaceful monster, or with several monsters in view next to each other. Do try to do it when you have a wand of enlightenment to zap and see what changed.
If you do not know the spell of "teleport away" and you are below experience level 12 (8 for Wizards), press ^T while trying out an uncursed ring. If it's teleportation, you will be told "You are not able to teleport at will." rather than "You don't know that spell."; this behaviour does seem to be intended. This doesn't work if you have teleportitis from eating the wrong corpses.
The following rings will be identified by putting them on; see invisible, if you are invisible and can't already see invisible; invisibility, if not already invisible; adornment, gain strength/constitution and protection, if not +0; and levitation, if not levitating anyway. Some other rings - like conflict - can be identified by observation of the effects and then #named appropriately.
If you gain intrinsic poison resistance while wearing an amulet versus poison or a ring of poison resistance, you will feel "especially healthy"; hence if you have only one unknown item of these kinds on, you know what it is.
If you are female and have a ring of adornment in your inventory (but not worn) an incubus will try to put it on you after sex, possibly asking you first. If you are male and have a ring of adornment with you, a succubus will either take or ask if she can take it after sex.
If you have two of a given ring, dropping one on a sink will give a message that can identify the ring to you (you don't need two, but since you usually lose the dropped one there's not a hell of a lot of point otherwise); this is very effective one you have a decent collection of rings. You will need to have a junk object on the sink, in case the ring is hunger; and many of these effects do not work, if blind.
These messages are as follows;
searching: "You thought your ring got lost in the sink, but there it is!" slow digestion: "The ring is regurgitated!" [these are the two cases where you get the ring back] levitation: "The sink quivers upwards for a moment." poison resistance: "You smell rotten <fruit>." aggravate monster: "Several flies buzz angrily around the sink." shock resistance: "Static electricity surrounds the sink." conflict: "You hear loud noises coming from the drain." sustain ability: "The water flow seems fixed." gain strength: "The water flow seems stronger/weaker now." gain constitution: "The water flow seems lesser/greater now." increase accuracy: "The water flow misses/hits the drain." increase damage: "The water's force seems smaller/greater now." hunger: "Suddenly, <junk object> vanishes from the sink!" meat ring: "Several flies buzz around the sink." [Effects from here demand that you are not blind.] adornment: "The faucets flash brightly for a moment." regeneration: "The sink looks as good as new." invisibility: "You don't see anything happen to the sink." free action: "You see the ring slide right down the drain!" see invisible: "You see some air in the sink." stealth: "The sink seems to blend into the floor for a moment." fire resistance: "The hot water faucet flashes brightly for a moment." cold resistance: "The cold water faucet flashes brightly for a moment." prot. shape changers: "The sink looks nothing like a fountain." protection: "The sink glows black/silver for a moment." warning: "The sink glows white for a moment." teleportation: "The sink momentarily vanishes." teleport control: "The sink looks like it is being beamed aboard somewhere." polymorph: "The sink momentarily looks like a fountain." polymorph control: "The sink momentarily looks like a regularly erupting geyser."
That said, price grouping still has some value for rings; if you can ID the real nasties in a group, you can try the rest on.
100 - adornment, protection, stealth, sustain ability, hunger, warning, protection from shape changers.
If only hunger wasn't in this group! Nothing else in here can hurt you by being worn long-term even if cursed (although beware the problem where you try on shape-changers in a shop and all the mimics whip you), and some of them will easily identify themselves to you.
[However, sustain ability can be awkward to identify - it's hard to generate a stat change on demand. If uncursed, you can become satiated, wait until the turn after you stop being satiated, eat something with a known nutrition value, and see how long you are satiated for - this lets you pick up on hunger.]
150 - gain strength, gain constitution, increase accuracy, increase damage, aggravate monster, poison resistance, cold resistance, shock resistance, invisibility, see invisible.
This risks confusion with the next group - but once you've got aggravate monster out the way (or have Stealth, which almost entirely nullifies aggravate monster), you may as well wear noncursed rings in this group (provided you didn't uncurse them - otherwise, there you are with -3 uncursed increase damage...)
200 - regeneration, searching, levitation, fire resistance, free action, slow digestion, teleportation.
Noncursed rings in this group; go for it. Teleportation is no problem if you can take it off, and see the ^T trick above. Just ensure you're down some HP for prompt identification of regeneration.
300 - conflict, teleport control, polymorph, polymorph control.
Without polycontrol, polymorph is a killer, since it will quite likely trash all your armour.
There's relatively few of these. The bad news is that they all cost the same. The good news is that, provided you are not polymorphed, trying on non-cursed amulets is pretty harmless. You might change gender (which is irritating), fall asleep (do it in a controlled environment) or be strangled (but then you just remove the amulet; uncursed strangulation is not dangerous); but this is well worth it for the possibility of donning life saving, and in any case these harmful types are nearly always generated cursed. Again, the wand of enlightenment technique is very useful here.
Of the non-harmful ones, ESP becomes known pretty well right away. Reflection is bound to become obvious after a while. Magical breathing can be tested for by stripping and jumping in a pool - you'll crawl out, if it's not (beware; if you can teleport, you often will, if not wearing AoMB). In theory you could also test for magical breathing by overeating and seeing if you die, but this has an obvious drawback. Versus poison is hard to identify if you're already poison resistant (see also the note in "Rings" if you're not), and life saving is hard to put to the test (but you often find them round monsters' necks, the standard way of IDing them - hence, an amulet dropped by an intelligent necked monster is probably not life saving - but it's not impossible.)
As mentioned above, Vlad's always has life saving and strangulation.
See also the #name trick in the "General" section to weed out ESP very easily.
Of course, the 'plain' spellbook is blank paper, and the 'papyrus' spellbook is the Book of the Dead. Vlad's always contains a spellbook of invisibility, and the Wizard will bring a spellbook of dig to the Plane of Earth.
Any blessed spellbook can be read successfully, and any spellbook granted you by your god will be blessed. Of course, there is no guarantee that you can cast the resulting spell. :-)
The base price of a spellbook is always 100 times the spell's level, making for easy identification of those one can safely read; obviously, however, the surcharge can confuse a level 3 spell with a level 4 spell.
The effect of reading a cursed spellbook is the same as that of failing to comprehend an uncursed spellbook, so normally you need to check cursedness before doing anything with a spellbook.
The question, then, is what level of uncursed spellbook you can safely read. It's easy for wizards, who receive a warning if they might not succeed, but the rest of us have to chance it. The effects of a too-hard spellbook are very severe, and I prefer to shop-ID the level of all spellbooks and only read safe ones. You will fail to read a spellbook if a random number between 1 and 20 is greater than (Intelligence + 4 + half XP level - twice level of book); hence, you can only read safely if this total is 20 or more.
Odd XP levels are useless for reading books; a level 3 character is equivalent to a level 2 one (and a level 1 character might as well be level 0). With that in mind, a level 0 character needs an Int of 18 to read a level 1 spellbook safely. Every 2 XP levels past that lowers the Int requirement by one, but each extra level of the spell increases it by 2. The chance of failure is 5% for each point of Int you are short. A moment's thought will reveal that there's not much point in spellbooks unless you have a high Int or a high XP level; at the high end of the spectrum, a level 7 spellbook requires an XP level of 24 to read safely even with Int 18.
If you can't be bothered to do the numbers, there's a table at <http://www.steelypips.org/nethack/spellreading.html> you can refer to.
That said, a low-level spellbook cannot paralyse you for very long (but more than long enough for a cockatrice to stone you), but although the worse spellbook aftereffects are generally seen at higher spell levels, the 'teleport' effect is most likely at low levels - a level 1 spellbook will give it every time - and being *bamf*ed across the level when paralysed is a good way to get killed. There is a sharp increase in paralysation times at spell level 3 and above; levels 1 and 2 can only immobilise you for 1-3 turns at most, which you may be willing to chance, especially since the probability of failure will be low. The particularly bold may even want to try level 1/2 spellbooks of unknown cursedness.
Unless you have monstrous Int and XP level, or are a wizard, reading unblessed books of unknown spell level is asking to be killed.
You can apply the same writing technique to unknown spellbooks as is discussed under "Scrolls".
These price groupings are pretty useless, to be frank; if you identified every other spellbook in a group, you can probably read the last one safely anyway.
There's not much to say about weapons, save that - like armour - a shopkeeper will increase the base price by 10 zorkmids for every point of positive enchantment. If you know the base prices for every weapon and piece of armour (which I am not, no, going to list here), you can easily determine which these are. Better yet, no weapon or armour generated with positive enchantment is cursed; just fling 'em down in a shop and pick up the expensive ones. Beware items from bones piles!
If you have several stacks of objects that stack, like daggers or arrows, the largest stack is probably uncursed +0.
Naturally, a named weapon (not found in bones) is always an artifact weapon, which are occasionally randomly generated.
If a throwing weapon or piece of ammunition 'slips' or 'misfires' when you throw or fire it, it is cursed; but cursed weapons and ammo will not do this every time they are used. Exception; any greased item may also slip or misfire.
Armour is much easier, since you can discover the +/- status just by trying it on (once you know it's not cursed, and with the exception of the autocursing types of headgear; of course, the enchantment pricing technique above helps spot blessed armour); but there are a few types of armour with shuffled descriptions. Positive enchantment can obscure price groupings, but that's OK (again, apart from those kinds of headgear) because such items are then always non-cursed and can be removed (and as soon as you try it on and learn the + status you know what group it's really in.)
Nearly all fumble boots, levitation boots, helms of opposite alignment, and gauntlets of fumbling are generated cursed. Not all, alas, so one may still get uncursed helms of opposite alignment. Nevertheless, if you (as I do) #name a known cursed armour item "cursed once plumed" or similar, and then find a second piece of the same type also cursed, the odds are good that it is one of these; conversely two noncursed items of the same type (without also finding cursed ones) suggest that the item is not of this type (but if it's not a helmet, you might as well just try it on.)
One type each of magical gloves (gauntlets of power) and boots (kicking) is made of metal, not leather, and so rusts and corrodes where the others burn and rot; this might be useful if found in a bones pile or if you have spares and can change into a monster that eats metal or leather. You might also try wearing non-cursed boots and looking for changes in your spellcasting chances (a lack of a change does not guarantee non-metallic boots - a full discussion of these chances is beyond the scope of this document). This is useless for gauntlets of power, because they automatically ID when worn. Also, you could immerse the item repeatedly and see if it rusts (or wear boots and let a rust monster pound on you, I suppose). Beware; if your Luck is high, many immersions may be needed. If you have an unidentified touchstone or any other grey stone, rubbing it on metal armour produces "scritch, scritch" or "scratch marks", and non-metallic armour produces brown streaks. You can't do this with an identified touchstone. No, I don't know why not.
If you use a stethoscope on monsters, you can gain a good idea of the enchantment of their armour.
The most straightforward of these are the 'conical hats'; the cornuthaum and dunce cap. If you're not a wizard, you don't care; if you are, you can either be prepared to uncurse the dunce cap (not with the spell of remove curse), or use the fact that the base cost of a cornuthaum is 80 and that of a dunce cap is 1.
Next, the plain helmet, helm of brilliance, helm of telepathy, and helm of opposite alignment - plumed, etched, crested and visored. Plain helmets are cheaper (base cost 10 vs. 50), often found on soldiers and minetown guards, known to those classes that start with knowledge of armour types, and if you sell (actually sell, not get an offer on) a plain helmet to a shopkeeper it will be identified, so that's pretty easy. The other three are hard to tell apart, and opposite alignment autocurses and blows away your divine protection; but, if you're willing to take a chance on it, telepathy is pretty handy. (If one of these helms doesn't do anything, it's most likely +0 brilliance. Or you forgot to take off your amulet of ESP? Or a +4 plain helmet...)
However, if you are in your Quest and you try on a helm of opposite alignment, you "narrowly avoid losing all chance at your goal" (or "are suddenly overcome with shame and change your mind", if you already changed your base alignment); you still lose divine protection but it doesn't end up autocursed and stuck to you.
See also the #name trick in the "General" section to weed out brilliance very easily.
A 'slippery cloak' is always oilskin; a 'faded pall' is always elven; an 'apron' is an alchemy smock. The cloaks with shuffled descriptions are protection, invisibility, magic resistance and displacement; the tattered cape, opera cloak, ornamental cope, and piece of cloth. Protection and displacement both immediately ID themselves when you wear them. If you're already invisible, it can be hard to tell invisibility from magic resistance (if you have the HP, zap yourself with a wand of magic missile or striking). It may be sensible to try on these cloaks even if not known uncursed; they all do useful things, and a cursed cloak only prevents you from changing body armour (or shopping, if invisibility.) Note that protection and displacement have a base cost of 50 where the other two have a base cost of 60.
A cloak of magic resistance could also be identified by walking into traps of types that it negates; teleport, drain energy, level teleport, polymorph (carries its own risks) - or by suffering attacks that it negates, although taking a touch of death and seeing if you die does have certain drawbacks. You'd obviously need not to be carrying any other magic resistance item.
A polished silver shield is always reflection; if blind, it's a 'smooth shield'.
Four kinds of gloves are shuffled; leather (again, classes who recognise armour get a bonus here, and actually selling one will ID it), fumbling, power, and dexterity; these are old, padded, riding and fencing gloves. It's hard to justify trying these unless known uncursed; fumbling is awkward and +0 dexterity is useless. You can't tell +0 dex from leather if you don't already know leather, which is a nuisance. Gauntlets of power are made of metal. Leather is very much cheaper; base cost 8 versus 50 for the others. Guards and soldiers, again, often have leather gloves.
Boots are pretty awkward, because there are many types. 'Walking shoes', 'hard shoes' and 'jackboots' are just low boots, iron shoes and high boots, respectively. However; speed, water walking, jumping, elven, kicking, fumble and levitation boots are shuffled into jungle, combat, hiking, mud, buckled, riding and snow boots.
Elven and kicking boots are cheap, with a base cost of 8. Fumble and levitation boots cost 30 (and are nearly always cursed), and the others 50. Since fumble are the only harmful kind (and the cost 50 boots do their job just as well if cursed), this can be useful.
Elven monsters are very likely to start with elven boots, and if you are an elf you began the game knowing elven boots.
Levitation, elven and speed boots ID themselves right away, unless you are already levitating, stealthy or very fast; not being stealthy can be hard to arrange, though. Jumping boots can be trivially identified by trying to jump; fumble boots (uncursed, I hope) by wandering around in them.
Kicking and water walking boots are more difficult. Kicking boots may be distinguished because of the fact that you will always kick down doors when wearing them (if you have a lot of doors to spare - obviously, you can never be quite sure), but a more straightforward method if you are not a monk, samurai or sasquatch is to kick any object with and without the boots on; with kicking boots on it will move between 1-3 further spaces. Kicking ranges are also increased on ice, so don't compare on-ice with off-ice ranges. Monks, samurai and sasquatches can still try kicking doors, but they are quite likely to kick down doors anyway. As mentioned above, jumping into pools IDs water walking right away, and will also sort out kicking boots when they rust.
There is relatively little potential for confusion amongst tools, but there are a few complicated types, and the question of whether the tool you have is cursed is always interesting.
4 objects are described as 'bag'; the sack, oilskin sack, bag of holding, and bag of tricks. The sack is considerably cheaper (2 vs. 100), and you may well start with one; the bag of tricks is trivially identified by #looting or applying it (be equipped to handle the results. #looting will do at most 10 damage, where applying may summon an arbitarily nasty nasty and will cause a shopkeeper to charge you for that use, if it's not your bag.) The other two can be sorted out by finding a bunch of junk objects (rocks, say) that just make one Burdened and stuffing them into the bag; if you aren't Burdened, it was holding. Take them out, drop two (now un-Burdened), and put them back in; if you are Burdened, it's cursed holding. If objects disappear upon applying, it's cursed holding, and you want to take out all the remaining objects now. Use #name appropriately.
If you find a bag in a bones pile, it is mostly likely cursed and full of juicy loot. You may not want to chance its being holding (and losing some of the loot), so if you can lift it at all, it's probably a good idea to uncurse it first; if not, clear other objects away and give it a zap of cancellation (if possible) - this doesn't harm the contents. It's not clear to me that cursed holding can be generated outside of a bones pile. Of course you may be willing to sacrifice some of the loot to have the rest readily available.
Another way to sort out the bags which are not tricks is to put water-damageable objects such as junk potions and scrolls into them (be sure it's not cursed holding, but since holding's easy this is best for oilskin sacks and plain sacks in the absence of price-ID) and immersing it repeatedly, checking to see if the contents are damaged. With high Luck you may require many immersions.
There are two objects called 'lamp'; the oil lamp and magic lamp. Oil is cheaper (cost 10 vs. 50), and magic is inexhaustible - either kind may 'splutter' and fail to light if cursed. Four approaches; check the price, bless one and try #rubbing it, just light the first you find and see if it ever gets used up, or try to refill it with a potion of oil (but you might as well wait and see if it gets exhausted, unless you have 2 kinds of lamp and want to know which is which right away). Regardless, it's worth #naming the first lamp you find 'lamp 1' or something, so you can tell if you've actually got both flavours.
There are two 'whistles'; tin and magic. Apply them; a high whistling noise is tin and strange is magic. Easy. You may not need to #name magic, if you have a pet to be summoned. (These objects are unlikely to be cursed, but 'high-pitched humming' is magic, 'shrill' is tin.) Watchmen are often generated with tin whistles.
For all musical instruments, you should improvise unless you are trying to open the Castle drawbridge (not that you get a choice with drums).
Two 'flutes'; magic and wooden. Magic flutes, if charged, produce 'soft music' (and put monsters to sleep); if not, they are like wooden flutes - they 'trill' or 'toot' (and charm snakes, in the former case, which is likely if you have good Dex or XP level). However, magic flutes are never generated uncharged, so this should not normally be an issue.
Four 'horns'; tooled, frost, fire and plenty. Frost and fire ask for a direction (same issue that an uncharged one is like a tooled horn); a horn of plenty makes food (an uncharged one does nothing, but it's the only horn that does, so you know what it is.) Beware; tooled horns awaken monsters.
Two 'harps'; magic and wooden. With the usual proviso about the uncharged magic version looking like a normal one, the magic harp produces 'very attractive music' (and charms monsters) and the normal one 'produces a lilting melody' or 'twangs' (and charms nymphs, in the former case.)
Two 'drums'; leather and earthquake. If charged, it's not hard to work out which one you have.
All bells and bugles are normal, except the 'silver' Bell of Opening.
Various tools are easily identified, but you may be unsure as to their cursedness status (although, as mentioned above, only light sources, grease, crystal balls and figurines will normally be generated cursed). With a cursed camera, you will photograph yourself half the time. A cursed towel or blindfold cannot be removed, and (a)pplying a cursed towel covers you in gunk (useful in emergencies if you have no other way of blinding yourself). A cursed stethoscope may well cause you to hear "your heart beat" (even if you are polymorphed into a heartless monster, alas). A cursed leash will strangle your pet - potentially fatally. A cursed mirror will fog up and not reflect. Cursed bells summon nymphs; the cursed Bell of Opening summons undead. Cursed tinning kits make cursed tins. A cursed unicorn horn gives you one of several nasty conditions, potentially fatally. Cursed grease greases your hands. Cursed land mines and bear traps tend to go off on you. Wax candles burn for 400 turns where tallow candles burn for only 200, so if you have some obscure need to identify candles (perhaps to eat wax candles without breaking vegetarian conduct) you could light one, wait for it to burn down, and #name others that stacked with it. That's about all the interesting ones.
Rocks are technically 'gems', as are grey stones. Grey stones come in four flavours; flint stones, luckstones, touchstones and loadstones. They can be price-IDed; luckstones have a base value of 60, touchstones of 45; the other two have a base value of 1. Loadstones are always generated cursed; other gems, uncursed, so apart from bones files you need not fear carrying around a cursed luckstone. This also makes spotting loadstones very easy for Priests.
You can only kick a loadstone across the floor if your Strength is at least 22 and you are either wearing kicking boots or are a samurai, monk or sasquatch; even then you will not move it reliably. If you are on ice, an extra 1-3 is added to all kicking ranges (which might otherwise be negative); if you can kick a grey stone on ice, it's best to kick it to a non-ice space before deducing anything. A grey stone that cannot be kicked owing to an awkward position presents a difficulty; so does one in a chest or box. If you can, you can try locking the box and #forcing it with a blunt implement to destroy the box; but if you break the lock, you are out of luck unless you have the spell of wizard lock or a wand of locking. If you have the patience you could count up your total weight and arrange matters so that the weight of the box and a loadstone would take you to a different burdening status to that produced by the box and a harmless stone. If you can afford to uncurse the thing, you can always pick it up and see if it's really heavy; remember to #name it before dropping it again if it is a loadstone. To my knowledge, there's no way to #name a loadstone without picking it up, so even if you kick-test one you've got no way of marking it unless you have holy water to burn.
See the #name trick in the "General" section to weed out luckstones very easily.
Touchstones are easily identified provided you're not blind; #rub any unknown grey stone on a hard object that is not gold, silver or wood, like an iron weapon. If it's a touchstone, you will hear "scritch, scritch". Once you have a blessed touchstone - uncursed if you are a gnome or an archaeologist, the latter of which begin with a touchstone - you may rub it on any gem or stone to identify it, which certainly helps with the other grey stones.
As for flint and luckstones, #name any grey stones you can't kick-test or determine are touchstones by #rubbing; once you have two flavours, you know you have a luckstone. Alternatively, only flint stones and touchstones are generated in piles of more than one; you may use enlightenment to tell that there is a luckstone in your inventory (you will always have "extra luck" or "reduced luck"); or see the discussion of the guaranteed items in the Mines below.
Unusually, gems of certain types are only created below certain depths in the main dungeon when creating new levels (note, however, that unless you dig a gem out of the rock it's hard to be sure it was generated then). Each gem in the table below lists its minimum depth in brackets where that depth is greater than 1.
Gems come in two flavours; soft and hard. You can engrave in the floor with hard gems, but only write in the dust with soft ones. All hard gems are valuable (but not all soft gems are worthless). This provides sufficient information for most purposes; you don't need every valuable gem to get all a shopkeeper's goodies (but you _will_ need scrolls of identify to actually ID your valuable gems and sell them) or to get luck out of unicorns. If you are interested in IDing gems at all, this is the technique that reveals the maximum information for the minimum amount of effort.
You can identify amethysts with the trick in the 'potions' section.
A second way to identify classes of gems is by flinging them to unicorns. This also has an effect on your luck - however, it's equally likely to be negative as positive if the unicorn is not coaligned, so best to stick to coaligned unicorns. The unicorn keeps the gem if it's valuable and you haven't #named it, so I usually #name the target gem 'valuable red' and fling it; if I get it back, I can then #name it 'worthless red'. If it's not #named, the unicorn 'graciously' accepts glass, and you need another one to actually #name.
Glass golems, when killed, create worthless glass but not valuable gems. I should add a disclaimer here; I've never seen a glass golem drop anything, and I don't see why one shouldn't happen to be carrying a valuable gem, which might confuse the issue. However, Dylan O'Donnell tells me that a glass golem will never pick up a gem.
The spell of stone to flesh turns valuable gems into meatballs, but leaves worthless glass intact. If you don't mind losing the test gems, you can #name unknown gems "valuable <colour>", zap them, and #name the ones left over "worthless <colour>".
The gems in the 4 corners of Fort Ludios are always diamonds, emeralds, rubies and amethysts. In 3.4 the Gnomish Mine bottom has become considerably more complicated, alas. There are three randomly selected endings, two of which have layouts from familiar versions of NetHack. Portions of these next paragraphs are quoted directly from Dylan's Dungeon Gazetteer.
In general, each gem or piece of glass (or flint or touchstone) listed below may become a pile of 2 at generation time, with a 1/6 chance. Also, there also a chance that any of the level's randomly scattered gems could end up on a predetermined pile; in that case it would be on top of the pile.
The first of these is "the Mimic of the Mines", a variation on the only mine ending in still older versions of NetHack; this is the ending where you descend into an irregularly shaped area which is dark. There are seven awkward or secret spots on this level, six of which (randomly assigned) will contain;
The second ending is the Gnome King's Wine Cellar; in this one you start in a wide short lit rectangular room with a single doorway in the right-hand wall. Here the gems are in a 2x2 rectangular hole in the rock you can dig out; this contains at least two diamonds, two random gems (NW); two emeralds, two random gems (NE); one ruby, one emerald, two random gems (SW); two amethysts, one ruby, one random gem, and a luckstone on top (SE). Often the random gems will not interfere with colour-based ID of the valuable ones; if you find two grey stones in the south-east pile, the top one is the luckstone (but kick it off anyway out of paranoia?)
The new ending is the Catacombs, where you begin in a lit square room with only secret entrances. Randomly placed on the level are two diamonds, three emeralds, two rubies, and two amethysts; and there are three secret spots - one empty, one with a level teleport trap and a luckstone, and one with a level teleport trap and a flintstone. Getting the stones off the traps is left as an exercise for the reader.
Gem pricing in shops is curiously complicated. Selling prices (where the gem is un-IDed) leak a little information in a way I still believe is an inadvertently possible abuse, and hence I am not going to document this - especially since any compilation option that changes object ID numbers will invalidate the whole list. However, the buying price of each worthless gem is randomly set (each game, not each gem or each purchase) to that of one of two valuable gems of the same colour; hence if you find a soft gem of a given colour with a price that does not match one of the possible worthless glass prices, you know it is still valuable - in particular, the dilithium crystal qualifies here and sometimes the various variable-colour gems (see below). The table below has a '*' next to the name of all gems that have a duplicate price for worthless glass.
Colour grouping can help sort out gems - unfortunately, various gem colours are shuffled at game start time, to make our lives miserable. The table below indicates the chance that the listed gem is of the listed colour (but a given gem will always be the same colour in a particular game - if one turquoise is green, they all are.)
|white||diamond* 4000 (25)||dilithium 4500 (28), opal* 800, fluorite 400 (25%)|
|red||ruby* 3500 (22)||garnet 700, jasper* 500|
|orange||jacinth* 3250 (19)||agate* 200|
|blue||sapphire* 3000 (16), aquamarine* 1500 (50%)||turquoise 2000 (50%) (7), fluorite 400 (25%)|
|black||black opal* 2500 (13)||jet* 850, obsidian 200|
|green||emerald 2500* (10), aquamarine 1500 (50%)||turquoise 2000 (50%) (7), jade* 300, fluorite 400 (25%)|
|yellow||citrine* 1500 (4), chrysoberyl* 700|
|y.brown||topaz* 900||amber* 1000|
|violet||amethyst* 600, fluorite* 400 (25%)|
[In addition, there's one kind of glass for each colour.]