If I want to make someone blind until sunrise/sunset, can I do it with Perdo and at what guideline?
Can I give someone a medium wound that will vanish in 2 minutes?
The rules state that unnatural changes with Perdo, such as destroying something's weight, are temporary, but I can't find any reference to whether natural changes can be temporary if the magus wishes.
And if they can't be, is there any way to blind someone until sunrise/sunset? Muto?
The easiest way to 'fake' temporary Perdo effects like these, tend (IME) to be abusing Muto.
You will need T: Part from time to time, but... temporary blindness? Turn their eyes into pebbles! - Or acorns or elbows or ... whatever suits your Arts.
A temporary wound? More tricky. Not sure how I'd do that.
Maybe Mentem? Convince them that they are wounded, while they actually aren't?
CrIm an insubstantial but opaque illusory blindfold on them. Definitely requires an extra magnitude for movement; might require a corpus requisite, to keep its location fixed relative to the victim's body.
Can also CrX a physical blindfold of just about any of the Forms, which probably wouldn't need the Corpus requisite (being physical, it would move with the head it's tied onto automatically) but would need some way to keep the victim from just untying it or slipping it off or slitting a peephole in it; the insubstantial illusion doesn't have that problem.
There's a few guidelines in Rego Corpus that could be useful here with the eyes in particular.
Level 2: Make a target lose control of a body part. - could be useful on eyes to make the target unable to visually focus
Level 5: Hold a target's body motionless. - with target part to force the eyes to remain shut.
Perdo Corpus tends to inflict wounds that blind and then need to be healed. Perhaps adding a requisite could help with a temporary blindness that doesn't need to be cured over downtime, but that seems counter-intuitive.
Take the Harmless Magic Flaw in HoH:MC, page 87? Then all your non-ritual Perdo spells can be temporary.
Pe effects which remove a quality from an item (for example, opacity from metal) are by nature temporary.
If destroy major sense (base 20) is seen in this light then yes, in fact removing sight for a sustained duration is the correct way to use the effect.
on the other hand target:part for eyes and inflict minor wound will blind them until they heal the damage.
Destroy one property of a person (weight, solidity) is base 40, and in principle there is likely to be some property which would effect vision that could be thus removed for a given duration.
Thanks all. Interesting range of answers here. It feels a little counterintuitive for temporary impairment not to be Perdo, when the same thing but permanent is Perdo... so I wonder if some kind of guideline for it may be useful as a HR. But anyway, plenty of possibilities to consider from these responses.
It would definitely improve Perdo as an art. As it is it’s great for those things nothing else can do (DEO-like effects, harming and killing) but it could use a slightly wider portfolio to make it a decent technique. And overlap is fine, it doesn’t matter if that thing can be accomplished via another technique the other techniques have significant overlaps.
It seems to me you want to do it with Perdo Corpus, rather than using other Forms -- note that PeIg can do it (by destroying light), PeIm can do it (by destroying species), PeAu can do it (by making air foggy), and PeMe can do it (by making someone constantly forget what he is seeing, or making him unable to make sense of what he is seeing).
In this regard it's worth noting that guidelines are just ... guidelines, so you should not feel too constrained. For example, making someone sneeze uses a PeCo level 3 base, and the only base 3 guideline listed is "Do superficial damage to a body (for example, remove its hair)". So, you should be able to make someone blind for D:Sun with vanilla PeCo. I would be tempted (but see below) to say that to blind or deafen someone for D:Mom as if after a flash of lightining or a peal of thunder should use the Base 3 guideline - it's a little like the sneeze example above. To make someone feel as if having sliced onions for the last few hours, should be Base 4, as per "cause someone pain but no real damage" (the same guideline for PeAn makes a beast unable to do anything in any round in which it fails to roll 9+ on stress die + Sta + size). Incidentally, "cause pain but no real damage" can probably "simulate" a medium wound too.
That said, there are two things to keep in mind. The first is that you should try to keep the result balanced with other effects. Making someone blind for a month or more (as a Heavy wound) is Base 20; making them blind for a day probably should not be that much easier (if easier at all), because it's not that much less effective. The second is the peculiar nature of Perdo, which does tend to create permanent, natural effects. This is something that even Bonisagus remarked upon (when Mercere lost his Gift), and I think that some Criamons might tie it to the "era" of the world.
It occurs to me that cripple limb (base 15) with target part aiming for the eyes might be able to do this, or the level 5 guideline of "hamper person without injury" which this would certainly do...