Some other potion questions.

[Yqatuba]

1. How do you tell what a potion does without drinking it?
2. Can you have a potion that casts a harmful spell when you drink it? (and use it for a sort of trap?
3. Do potions detect as magic?
4. What happens if you try to use a potion in an antimagic field/dead magic zone? I'm guessing you just swallow it and nothing happens.

[thorin001]

1) perception check or the usual detect magic
2) Yes
3) Yes
4) There is no clear RAW on this. My best interpretation is that the potion applies its effects and is immediatel suppressed like any other spell in such an area. So an instant effect like a Cure spell woud be wasted. One with a duration would still count the time in the AM effect against its duration, but would start immediately working at full effect once out of the AM effect.

[Kayerloth]

1) Also Analyze Dweomer and Identify. Other clues may exist as well if the vial is marked, has an Arcane Mark on it or has other distinctive features leading to the use of Knowledge checks or Bardic Lore type abilities (or spells) to figure out what it might be (or at least narrow the field). Pretty much no limit here depending on the time and creative effort the GM and PC(s) want to put into it.
2) yes, or poison with Magic Aura on it. (or a vial of Sovereign Glue <oops>) going to be tough to eat for a while)
3) Absolutely unless the magical aura is messed with via things like Nondetection or Misdirection.
4) I'll second thorin001's response.

[mardaddy]

Spellcraft check. DC is 15+ Spell level.

Identify gives a +10 to the check, it's not automatic.

Regarding detecting a potion that has a harmful effect, well... now you (DM) have to determine between is it a harmful spell in potion form, or is it a cursed potion? If it is just a harmful spell, the original check will reveal it. If it is a cursed potion, it will detect as something helpful unless the DC is exceeded by 10, THEN it will be known as cursed.

Examples:
1) Cure Lt Wounds DC16+ Spellcraft check to ID as such.
2) Inflict Lt Wounds DC16+ Spellcraft Check to ID as such.
3) cursed Cure Lt Wounds (actually Inflict Lt Wounds) DC16+ Spellcraft check reveals it as Cure Lt Wounds, and unless a 26+ is rolled, it is not detected as cursed.

One trap I've used is labelling an Inflict Lt Wounds Potion with a Cure Lt Wounds label. Most players go with it with only the detect magic and just assume it's labeled right. Only works once, lol.