PeAu 05 - destroy one aspect of air
PeIg 10 - destroy one aspect of a fire.
PeAq 15 - destoy one aspect of water
PeTe 20 - destroy one aspect of dirt
This would be my scaling , based on "substantiality" of the elements.
It does make me conjecture , whether one can destroy the base nature of air and make it solid for the duration of a Perdo spell.
Auram spells normally have to be cast at Sight Range to be considered natural.
Destroying Air with great precision raises it by at least 01 magnitude.
And extra magnitudes (+01 to +04) based on how unnatural the effect.
Which is why i give a Base of 05 to Air , due to effect modifiers.
My inclination is to have weight or substantiality destroying spells higher ,
based on elemental differences.
Which is why i think a Terram base of 15 is a bit low , due to how easy it is in comparison to doing the same to Auram.
Which certainly goes a long way to explain Hamlet's shock at seing his father, or Macbeth's at seing Banquo!
Fair is foul, and foul is fair...
â€œPeAu 05 - destroy one aspect of air,
PeTe 20 - destroy one aspect of dirtâ€
On the idea of walking thru walls, just drop the special effect and the level of the spell stays the same for your base effect. I am leaning towards the level 15 as base effect, rather than your 20, but this is a matter of personal taste.
On the subject of Auram, I was basing the effect on the level 10 effect of destroying a kind of air: noxious stench, mild poison, etcâ€¦(pg 128) and Auram spells usually affect air as phenomena (winds, odors) (pg 125). I see your point on base 5 to destroy one aspect of air based off of the same table on page 128, destroy stale air at level 4 and make air stuffy (unhealthy) at level 3. I doubt that air could be made solid with a Perdo spell, as this seems to grant an improvement.
Just some musing,
If only Apromor was here, he would be able to sort this mess out
One could equally argue that making stone "as unto air" air is a Muto effect.
Destroying a property that cannot be naturally lost is covered by Perdo.
I don't see an improvement in Auram , if it is made solid.
As opposed to a wall being improved by being able to be walked through.
What happens to the rest of the wall , if part of it suddenly has no substance?
With a concentration duration and at walking speed ,
any damage to the surrounding parts of a substantial wall is probably minimal.
But as the spell is not creating a structurally sound door or archway ,
there should be some possibility of damage.
A Stress roll for the wall , might be the way to go.
And i would expect repeated castings through the same section of wall to have a cumulative effect ,
unless a Creo effect is used to repair cracks.
Any damage would start as small hairline fractures and get successively worse over time ,
as this is a natural tendency of damaged stone.
Ravenscroft, this is the reason I enjoy Ars Magica. There seems to be always another way to tackle a problem. So going with your â€œStone as Unto Airâ€ suggestion:
MuTe 5 The Wall Without Substance
R: Touch, D: Mom, T: Part
Change the section of wallâ€™s property of solidity, allowing one to pass thru. Also with the special effect to keep from getting stuck in stone.
(Base 1, +1 Touch, +1 Part, +1 affect Stone, +1 special affect) - Change one property of dirt/stone
MuTe (Au) 15 Stone as Unto Air
R: Touch, D: Mom, T: Part Req: Auram
Change the section of wall into air, allowing one to pass thru; see thru; fire arrows; or others to cast spells thru. Also with special effect to keep from getting stuck in stone.
(Base 3, +1 Touch, +1 Part, +1 affect Stone, +1 special affect) - Change dirt/stone into a liquid or gas
With all the spells, I agree that they would indeed weaken walls. I like your idea of a Stress roll to see if cracks and fractures start to form, with the damaging increasing with repeated use.
As with Auram, I do agree that air phenomena (clouds, rain, wind) could lose its etherealness, but I am not sure that air itself could lose the same property. But solid clouds conjures images of Jack and the Bean Stalk, or better yet, solid wind becoming a battering ram. Forget walking thru walls when a windstorm literally batters the walls.
Hmm - the MuTe5 versjon mentioned in the last post would probably not weaken the wall, it just allows access (in a way fitting ones sigil - for some a door might open...)
Magicking a doorway in a stone wall (one not designed for it) won't weaken it? Ummm...
Otoh, it is in genre, so maybe it should only be a plot-complication consideration.
Hum. My approach would be to MuTe(He) a door into the wall.
Knock knock. Pass. Close the door. Door disappears.
No problems with walls falling to pieces.
Unfortunatly i dont have the guidelines at hand, but it feels like level 15.
My 4th ed. character has a spell named Orpheus's Journey, which turns any earth and stone he pushes against* into air, much as Lungs of the Fish turns inhaled water to air. The rock turns back again once he has passed, but the spell has a long enough duration for extensive tunneling. He uses it often, generally in conjunction with a spell for seeing through stone. I'm currently working on a 5th edition version.
*Simply standing on something does not count as pushing, of course, except perhaps in the case of a botch.
I don't know where i read this, but i just recalled this piece of superstitious belief:
If someone steps over a wall while it is still in construction, he opens a door by which fairy can enter/leave the building.
If you make that a fact in your saga, there would be quite a number of those "doors" ( Depending on how much attention your masons spent on not-stepping-over-walls...).
Now, if we interpret these "fairy-doors" as miniature-fairy-regios, then anyone with fairy-eyes or an adequate InVi-Spell could detect the door/regio and enter/exit it at will, thus stepping through the wall.