Several spells create, conjure, manipulate (etc.) mundane material. Typical spell-casting durations are instantaneous, but the effect is permanent. I want to understand when these spells leave a magical aura that might be detected by Detect Magic, for example. When is the result of the spell mundane vs. magical?
I'm going to come at this question from a couple angles.
According to the spell description for Detect Magic, spells and magical items have a lingering magical aura depending on their strength, even spells with an instantaneous duration. This aura lingers even after the spell has ended or a magical item has been broken. For the remainder of this answer, I ignore this effect and consider only non-lingering magical auras.
Creation of Mundane Material (void → mundane)
There's an instantaneous magical aura involved in the casting of the spell, but it dissipates as soon as the spell is cast, leaving behind only mundane materials with no discernable magical aura.
- Create Food and Water
- Create Drug
- Wall of Stone
- Minor Creation (technically this is both creation and manipulation of material, because it requires a tiny amount of substance as a spell component)
Manipulation of Mundane (mundane → mundane)
These spells move, shape, or manipulate mundane material into other mundane material. Typical durations are instantaneous. There is no magical aura before or after casting the spell, but an instantaneous aura exists while casting the spell.
- Move Earth
- Purify Food and Drink
- Transmute Mud to Rock
- Stone Shape
- Transfiguring Touch: Assuming the alchemical residue is mundane, this spell simply spreads it out over the surface of the target.
Magical Removal (magical → mundane/void)
These spells magically remove something from existence, whether the target is entirely mundane, entirely magical, or a mix.
Magical Manipulation (mundane → temporarily magical → mundane)
Some spells temporarily turn something mundane into something magical for a short time. Such spells usually have a non-zero, finite duration, during which the object has a magical aura. Before casting the spell, and after the spell's duration has ended, there is no magical aura.
- Animate Rope
- Statue: The target is magical for the duration of the spell, even in their non-statue state, because the spell remains active.
- Flotsam Vessel
- Disfiguring Touch
- Vacuous Vessel (assuming the vessel is mundane to begin with; otherwise the vessel has its own magical aura before and after the spell, plus another magical aura for the duration of Vacuous Vessel)
- Lighten Object
- Disguise Self
- Solidify Earth
- Decrepit Disguise
- Enlarge Person
- Obscure Poison
Some spells don't fall neatly into these categories or are unclear.
- Diamond Spray: Clearly the shards are created with a magical aura, but are the shards themselves magical? If a bystander were to pick up the shards after the spell was cast, would the shards be magical? (Would the shards even exist after they did damage?)
- Conjure Deadfall: Is the deadfall magical or mundane in between its creation and destruction? If the deadfall was suspended in midair, as by a strong updraft of air, would it have a magical aura?
- Flesh to Stone and Stone to Flesh: Although the petrified victim is "inert stone", is that stone fully mundane, or is there a magical essence? It likely isn't pure stone, because it contains a soul, though the soul doesn't register as either alive or dead.
- Nondetection: Although Nondetection protects a magical or mundane object against various detections — including Detect Magic — it does not prevent detections. (At that point, the involved parties would need to make an opposed caster level check, per the spell text.)
- It is unclear whether Nondetection creates its own, detectable magical aura. For example, if a creature were simultaneously under the effects of Invisibility and Nondetection, it is clear in the rules-as-written (RAW) that Nondetection would hinder the detetion of the magical aura of Invisibility, but it is unclear whether Nondetection would create its own aura that could be detected.
You can detect instantaneous effects
A spell cast leaves a magical aura once it dissipates, which can be detected if the caster uses Detect Magic quickly enough.
First you determine the strength of the aura. You detect the strongest of these two factors: The spell level or the caster level. In the case of an instantaneous effect such as a Wall of Stone, you use the spell level (caster level is reserved for items without specific clauses). This scales as follows:
- Faint: Level 1-3
- Moderate: Level 4-6
- Strong: Level 7-9
- Overwhelming: Level 10+ (Also known as deific)
Now you know how strong the aura is, you must determine how long it lingers for with a quick dice roll:
- Faint: 1d6 rounds
- Moderate: 1d6 minutes
- Strong: 1d6x10 minutes
- Overwhelming: 1d6 days
Also, be wary of the level 2 spell added in Ultimate Intrigue called Greater Detect Magic. This spell allows a caster to detect any magical aura created within 1 day per caster level (of the caster of Greater Detect Magic) as well as perform a host of other goodies.
While the stone wall made by wall of stone might no longer be magical, the creature with magical detection can potentially see what looks like a form of radiation coming off of it for a while.