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?
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.
Detect Magic says:
You detect magical auras. The amount of information revealed depends on how long you study a particular area or subject.
3rd Round: The strength and location of each aura. If the items or creatures bearing the auras are in line of sight, you can make Knowledge (arcana) skill checks to determine the school of magic involved in each. (Make one check per aura: DC 15 + spell level, or 15 + 1/2 caster level for a nonspell effect.) If the aura emanates from a magic item, you can attempt to identify its properties (see Spellcraft).
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".
You are skilled at the art of casting spells, identifying magic items, crafting magic items, and identifying spells as they are being cast.
Check: Spellcraft is used ... to identify the properties of magic items in your possession through the use of spells such as detect magic and identify.
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:
You are educated in a field of study and can answer both simple and complex questions. Like the Craft, Perform, and Profession skills, Knowledge actually encompasses a number of different specialties. Below are listed typical fields of study.
Arcana (ancient mysteries, magic traditions, arcane symbols, constructs, dragons, magical beasts)
Check: Answering a question within your field of study has a DC of 10 (for really easy questions), 15 (for basic questions), or 20 to 30 (for really tough questions).
You can use this skill to identify monsters and their special powers or vulnerabilities. In general, the DC of such a check equals 10 + the monster’s CR. ... Many of the Knowledge skills have specific uses as noted on the below table.
[ed: I don't have luck with quotes and tables, so this is just the "Task" column]
- Identify auras while using detect magic
- Identify a spell effect that is in place
- Identify materials manufactured by magic
- Identify a spell that just targeted you
- Identify the spells cast using a specific material component
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.