So, I ran a short campaign in ArM 5th ed. and one aspect of the system that seemed off to me was the system for the parma magica. I feel like an ablative system would seem more real, even if it involved more book keeping. Has anyone here tried an ablative parma with 5th edition? Has anyone tried using any sort of ablative parma rules with any edition? If so, how did it work out for you?
Thanks.
Parma Ablativa is on page 31 in True Lineages.
This is in the Example Discoveries section ,
but is designed for use in combat , not to replace the actual Parma mechanic overall.
It can be replaced in ten minutes , if the resistance is completely destroyed.
Not quite. I did use Partial Parma (allowing for blocking part of a spell, rather than only all or none of it) with 4th edition for a while. We determined it was too complicated.
I know it's a little off topic but why does it seem off to you? Didn't your player liked it?
After reading ARM5 several times, it seem to me that the parma magica was a very powerfull armor and that my players who'd just max it out and act as bravado all over.
After the fisrts session and every time a creature try a power on the almost always unarmored, physically puny and clumsy mage, my players almost turn white and they cheer when i describe the power of the creature bouncing away from them.
I don't know if it's a matter of description or players attitude toward statistics... What i'm shure is that the scariest thing for my players now is a grog with a club standing behind the door (that would probably be a one shot kill!)
-Bellysarius
I didn't mean I thought it was off because the mechanics didn't work well. The mechanics are fine. It was the underlying concept, that spells either are stopped by parma or aren't, that got to me. I felt it would make more sense to be able to hammer my way through someone's parma, given enough time. I guess it's just the simulationist in me. The system at Ablative Parma for example, seemed to be more in line with how I imagine the parma magica would work. The regular system just feels... arbitrary.
In short -as my connection to Atlas' server once more collapsed as I was submitting this post a second ago 
- the old version of ablative parma clashes with the 5th edition MR/Penetration rules due to the spell level being subtracted from penetration. If you implement ablation this will degenerate encounters to starting out with a few rounds of silly spells with the only purpose of breaking down the parma. These will tend to use less used parma specialisations and less used Forms and to strive to be as low as possible. Just think of a multitude of CrIm level 3 spells (base 1 +2 Voice) to put pink dots on the opponent..... To me that leads down a road of many more annoying opportunities than the standard on/not on parma.
If you must have ablation why not simply allow PeVi to gradually wear down a parma? Just as it can with Might. This would only require a simple HR and it would keep the spells used to bring an opponent's parma down sensible.
I didn't mean that those rules would be adequate as a replacement for the current parma rules, obviously the points you raise show that that would not work. Instead I am using them as an example of the flavor I feel the parma system should have. When I imagaine a wizard's magical defenses in combat I see them stopping spells until they get battered down, at which point the wizard would be completely vulnerable. This flavor was captured by those rules. Having spells be stopped by, degrade, or blow past a wizard's parma and giving the wizard the option of restrengthening their defenses captures this flavor. I understand that the mechanics would have to be updated, but would anyone agree that that system would give a richer picture of magical defense?
Yeah, maybe a richer flavor...
But i especially like the Perdo Vim option as presented by Furion.
Just allow it and make the magus in your saga use it as weapon against one another.
Anyway, i don't know if it's in my saga but i haven't got any mage casting spell at another for now. I only got creatures trying to blast away or use their power on the magus.
The only combat that i'll look forward to get between magus is a certamen. For now anyway...
-Bellysarius
Once you make such a change , anyone who does not put XP in PeVi is at a disadvantage.
A situation with specialist Verditius crafting Blasting Wands of PeVi to sell to other magi , could well occur.
Very Dungeons and Dragons as to the results , imo.
Serf parma but for now, i think to properly lower the parma magica of another mage you got to first penetrate his defense in order to affect the parma (is that it?).
So it's better to just blast him away with a regular spell directly... or the eternal weapon of choice, the pillar of fire droping from the sky...
Just as stated then, altought it brings flavor, it's kinda unbalance everything else in the system as tought. (And i'm sooo scared of the idea of a wand of PeVis festival and auction in every Tribunal...)
-Bellysarius
Well, I wouldn't use it myself, but for troupes wanting ablation it is to me the best alternative in terms of merging with the existing mechanics.
Yes, it would have to penetrate. Few magi would probably be able to make such devices with sufficient power - and making such items would probably call quite a lot of unwanted attention to them, especially if the item ends up being used against other magi (which is probable considering that it targets the parma). The main point is that this doesnt have to degrade to a market of 'parma busters'.
In any case the mechanics are already there - just take a look at Winds of Mundane Silence! Yet we havent seen a pan-European market for those either. The only difference would be that you wouldn't have to double the parma score and that the amount you surpass it is the amount it is diminished.
If you want parmas that are gradually worn down, you will have magi using time and resources on ways to do so no matter the mechanic. I can think of no better or fitting alternative than to use PeVi.
Use of spells and the market for items is highly campaign specific.
The core rules do not take a stance on the issue.
If PeVi spells were being used to ablate Parma , rather than just needing to Penetrate to affect spells ,
then i would see a proliferation of lesser enchanted device (page 96) Blasting Wands to do so.
Such things being against the Code , would likely create a Black Market , not prevent their use.
I sincerely doubt there's many with the sufficient scores to make lesser enchanted devices with a sufficient Penetration + sufficient Spell level to outmatch the Parma + ekstra levels to actually ablate the Parma.
Nor have you commented on the fact that something similar already exists plainly in the RAW.
Accepting that someone wants ablative parmas, I dare you to make an alternative instead of simply axing the ones presented.
As i was the one who posted the Ablative Parma quote after all. 
I did make a point of saying Specialists.
These would be Verditius , with an applicable Magic Focus and Cthonic Magic , for maxing out lesser enchanted devices.
(triple lowest Art Score)
A Magical Focus and Elder Runes for other devices.
If anything , i would use the Combat System for an Ablative Parma.
(though i have not as yet worked out how best to apply it)
Casting Total as Attack Total sort of thing.
Parma Score counts as Armor , Form bonus adds to Soak are possibilities.
Even if sharing the name, the mechanics are very different from one another.
All the very specialist things you mention might as well be used on the current Winds of Mundane Silence...
Your suggestion still lacks the primary thing the original poster was asking for - a gradually wearing down of the parma.
If i was going to use Parma , as per Armor in combat ,
i would make Armor ablative as well.
Physical or Magical protection degrades due to damage inflicted.
(i don't have specific mechanics in mind as yet)
The Ablative Parma from HoH:TL seems to work well enough as a mechanic , simple and easy to apply.
Making magical attack and defense similar to combat has the advantage of sticking to one mechanic.
Finesse is your Attack Ability , Parma your Defense Ability.
You could make Penetration Total for spells the Attack Advantage.
Give Parma "Wound Levels" , and as it is damaged or ablated ,
the "Wound Penalties" subtract from any total using the Parma Score.
When the penalties equal the Parma Score , it is gone.
Hmm...I think if I was making a HR for ablative Parma, I'd be tempted to have something like:
"Whenever an effect penetrates a magi's magic resistance, he must make a Concentration roll to maintain his Parma magica. The Ease Factor is 3 + the amount that the effect Penetration exceeded his magic resistance. If the roll is failed the magus may re-activate his Parma magica, which takes the usual amount of time."
This would seem to have the desired effect (it makes sense to hammer away at a magus with high penetration effects, until his Parma is destroyed) and doesn't seem to add significant rules baggage.
IMHO that still has the potential to reduce the first rounds in any such encounter to tossing as low level spells at each other as possible - to bring the parma dawn as fast as possible.
CrIm being among the lowest possible levels (doable at level 3 and still having R:Voice) attacking you opponent with pink dots untill he misses his Concentration roll seems a very silly but awarding strategy 
It also completely undo the Wind of Mundane Silence spells usefullness (when it comes to parma) as this is a much more powerful way of removing a parma.
And it still misses one of the main parts of former ablative parma HR - namely the gradual eroding of the parma.
Which is in what manner different to the mechanic presented in True Lineages?
Parma Ablativa is on page 31.
I think we need to consider that the reason penetration works the way it currently does was so that low power wizards could put their effort into getting a spell past their enemy's magic resistance (parma or otherwise). If we bring in the possibility of destoying an enemies parma (or more generally, their magic resistance) by simply hammering away at it for long enough, then the reason that penetration was given its current design is no longer a valid one.
In other words, redesigning the way the parma works, as well as other forms of magic resistance for the sake of consistency, will almost certaingly lead to the need to redesign penetration. The current penetration system is designed around the current method of magic resistance.