When using the Detect Magic spell to determine the properties of a magic item, do you have to succeed on the Knowledge arcana check in the third round of Detect Magic before you use the spellcraft skill to identify the exact properties?
Identify magic items
magicmagic-itemspathfinder-1eskills
Related Solutions
Since all of the Detect spells have a duration of Concentration, it seems to me like you have to concentrate to gain a benefit from them. If the Night Hag concentrates for 1 round, she can use any of her detect spells without having to cast it, but she doesn't get any information without concentrating. The difference here between continuous and at will is that the continuous version doesn't provoke an attack of opportunity. I don't think there's a solid rule on this, but I feel like this solution fits the normal behavior of the spells best.
Identifying a scroll is different from deciphering a scroll and neither requires expending the scroll.
Identifying
The detect magic spell determines if there're any magic auras in the area on the first round, the number of magic auras and the most potent aura in the area on the second, and where exactly those auras are and how powerful each is on the third. With a successful Knowledge (arcana) skill check (DC 15 + spell level), the caster can determine the aura's school of magic; this check apparently takes no time and is part of the 3rd-round detect magic effect. Doing this would tell the caster only the school of the spell or spells on the scroll.
A 3-round thorough examination of the object while employing the detect magic spell permits the caster to "[i]dentify the properties of a magic item" with a successful Spellcraft check (DC 15 + scroll's caster level). This tells the caster everything about the magic item, with apparently one exception. The caster knows whether the scroll is arcane or divine, what level spell is on it, what level the spell or spells are scribed at, and so on, but identifying doesn't reveal exactly what spell is on the scroll; to do that the caster must decipher the scroll.
These 3 rounds are in addition to the first 3 rounds leading to pinpointing each aura in the area of the spell detect magic. Events happen in order unless stated to happen simultaneously.
(The analyze dweomer spell also reveals these properties, but the word dweomer is difficult to say without laughing.)
Deciphering
To find out which spell is on the scroll (and subsequently be able to activate it) the caster must decipher the scroll, which requires a successful full-round Spellcraft skill check (DC 20 + spell level), a successful 1-minute Use Magic Device skill check (DC 25 + spell level), or the read magic spell.
After the scroll's deciphered, that scroll's always deciphered for that caster. No further checks need be made, and the scroll can be employed normally.
Don't conflate identifying with deciphering. The hairs are fine and difficult to split but the game splits them anyway: When a caster identifies an item's properties, he gets command words, number of charges, and so on (pretty much just like he read the item's description from the book) but not the name of the spell on the scroll; the caster gets that and the ability to activate the scroll from deciphering the scroll.
Note: That's weird and the Pathfinder Role-playing Game buries that on page 490: "The writing on a scroll must be deciphered before a character can... know exactly what spell it contains." This also isn't exclusive to Pathfinder--both the Dungeons and Dragons 3.0 and 3.5 Dungeon Master's Guides have the exact same language in their Deciphering a Scroll sections (pages 203 and 238, respectively).
Note: A solid but dangerous case can be made for skipping the identification step if the caster already knows what he's dealing with, much in the same way someone proficient with a sword can just whack fools with the sword instead of learning its maker, properties, and history before he starts using it. The DM rolls secretly to determine if a character deciphers gibberish via the Linguistics skill, but the player rolls openly to decipher a magic scroll via the Spellcraft skill or Use Magic Device skill, so right there the player will know it's a magic scroll and, if successful in deciphering it, know the spell on it. The character can then try to activate the scroll, but--and this is really a DM's call--the character still won't know any of the scroll's properties (such as it's spell level or the scriber's caster level) because the character's not identified the scroll's properties. Just as Fighter Joe can still take swings with a magic sword without knowing its exact properties, Wizard Jim can decipher a scroll and, if he meets the requirements, cast the spell from the scroll without knowing exactly what's going to happen. I've never seen a player want to do that, but I'd totally let him. That could be hilarious.
Other Tidbits: There are spells that straight-up answer questions and get information; one could possibly use those and make a big pile of information about a scroll. There are feats and classes that are scroll-specific, and those might be useful. I've ignored both because they seem to be beyond the question's scope.
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Best Answer
Use Spellcraft
Detect magic allows the target to see magic auras which, in turn, allows the caster to learn about the things from which those auras emanate.
Knowledge (Arcana) allows someone benefitting from detect magic (and similar spells) to learn the school(s) of magic involved.
Spellcraft allows someone benefitting from detect magic (and similar spells) to identify the properties of a magic item. Doing so requires "3 rounds per item to be identified and [the ability] to thoroughly examine the object". The way it's worded, I'm pretty sure that means identifying an item with detect magic actually takes 6 rounds: 3 from detect magic then 3 from Spellcraft.
So: someone with detect magic is looking at Goggles of Minute Seeing, a magic item based on the divination spell true seeing for 3 rounds. They could roll Knowledge (Arcana) to learn that the goggles emit a divination aura at the end of the 3rd round, even if they couldn't "thoroughly examine" the object. They could also choose to stop there if they had a bunch of magic items to look through and/or were pressed for time. Divination magic is rarely harmful, so such a party might just put them on and hope for the best.
If that person can examine the object for the next 3 rounds, they can also make a Spellcraft check to determine the properties of the goggles (ie., that they give a bonus on Disable Device checks; some GMs leave it at that, some give the name, and I've seen both work). Even without knowing which schools are involved in the item's creation, the person can determine the function of the item by careful examination.
Specifically...
Detect Magic says:
The ability to learn the aura(s) and the properties are listed as to separate abilities. If you needed to make the Knowledge check first, this would say something like "you can make Knowledge (arcana) skill checks to determine the school of magic involved in each. If you determine the schools to which the auras of a magic item belong, you can attempt to identify its properties".
Spellcraft says:
If you had to first know the schools of magic that the item's auras belong to, this would say something to that effect.
And, Knowledge (Arcana) says:
If knowing the schools of a magic item's auras were required to identify it, I suspect Knowledge would say something about it, even just a footnote on "Identify auras while using detect magic" that said doing so was a prerequisite for identifying the properties with Spellcraft.