Hi everyone, I'm trying to come up with a spell that can reduce the encumbrance of a suit of armour (such as chain mail) using muto terram.
Now the basic guideline that I'm using for this is MuTe: "Level 1: Change one property of dirt" (add two magnitudes for it to affect metal) (ArM 5 p154) So it seems logical that one property of, in this case, metal would be its weight. So I want to create a spell that could reduce the wait of metal armour such that it has significantly less encumbrance for the wearer. What would be fair/balanced for this spell?
Hauberk of Sublime Lightness is actually a Perdo Terram level 30 spell, however, not Muto. See HoH:S p.38.
Removing weight in order to reduce encumbrance clearly falls under Perdo in 5th edition. What a Muto effect might be able to do, however, is take a less-cumbersome set of armor and make it more effective. For example, a simple variant of Doublet of Impenetrable Silk (ArM5 p.118) could be used to improve the protection of a full set of leather scale armor from 5 to 8, thus making it almost as effective as a suit of chain mail for slightly lower load. It might be possible to negociate with your troupe/storyguide to improve protection even more using a higher Base, since the Base 4 in only a minor unnatural change. A major unnatural change (Base 5) could provide a better improvement, arguably making the leather as hard as iron.
As usual, there is different ways to skin this cat with magic.
Rego Terram: magic will assist in moving the armor, thus making is feels lighter. Think of driving assistance in a modern car. However, if there is a wind, the armor still weight its weight. Depending on the magnitude, you can achieve total control of the armor movement, and control it with your thought. Depending on the spell parameters, only the caster can benefit from it or only the one wearing the armour.
Perdo Terram: it destroys a property of the armour. In this case, its weight. The armour will float, a kid can lift it and its weight won't anchor the one wearing it if something push him. It is quite unnatural as it feels, looks and behave like an armour, except that it is much lighter. Everybody benefits from it.
Muto Animal (Terram): magic grants leather or wool properties of metal, specifically its hardness. But it does not look like an armour, it only grants a similar protection. It is not magnetic nor heavy.
IMHO, this way of reducing encumbrance would impose a penalty when trying to perform tasks while wearing the armor, simply because having to concentrate to control the armor's movement introduces a delay into the reaction speed. That is true even if it is enchanted as an effect, unless you link it with an InMe effect that reads the wearer's intention instead of relying on his actual movements to guide the armor.
I agree that there are many ways to skin a cat with hermetic magic, but some should be better than others. Reducing weight (and thus load) is the purview of Perdo. So altough something similar might be achievable through Rego, it should have some drawback. Whether that is a higher base, or side effect, is really up to the storyguide/troupe.
Otherwise you end up with no disadvantage from specializing in a given Art. Rego is already widely seen as much more flexible than many of the other techniques. Allowing it to cover even more ground isn't very wise, again IMHO.
I honestly feel like that is inconsistent with the entire concept of Perdo as per ArM5 p 78 Perdo: "Perdo can only make something a worse example of what it is. You cannot sharpen a sword with perdo, even though sharpening involves removing some of the the metal"
Removing the weight of an item while still retaining its bulk density is 100% an improvement on the item, there is no situation in which that would be making something a worse example of itself. Muto makes more sense in every way, you're unnaturally changing the weight property of the item to make it better at doing a specific thing.
But this isn't being represented in this case, the Pell says that it maintains its "bulk density" which is usually tied to both the weight and strength of a material, you can't remove weight from something like steel or iron wothout ruining the bulk density unless tou are turning it into something else like titanium, or something completely unnatural.
As per how the rules make use of load and protection this can only be an improvement and is not suitable to perdo.
The exploration of Perdo to do things other than destroy has been explored in the games before. Perdo Terram destroys the weight property of an object of terram. Muto changes a thing of terram into another thing. And this concept of Perdo making something worse than it is, is largely a subjective understanding. Obviously, one doesn't use the Veil of Invisibility, a Perdo Imaginem spell with the expectation that you are more easily scene when using it...
No, you can't normally remove bulk density, but with magic, based on the guidelines available you can. You can't make wood as hard as metal in RL, but there are magical guidelines that allow that. There's also a Perdo spell in Covenants that cleans a lab, which I personally hate, but it's canon. At this stage, in the life of Ars Magica 5th Edition, you won't see errata to correct any errors you might perceive.