New Virtue: Vis Affinity

I have an idea for a new virtue, and I'd welcome any thoughts.

Vis Affinity (Minor Hermetic)
Your magic is especially well attuned to a particular type of Vis (select any one Technique or Form). You are instantly able to identify this type of Vis without the use of a spell, and gain a bonus to spells to determine whether the Vis is tainted in any way. Additionally, you use less of that type of Vis when you utilise it for spells or laboratory activities: you only need to use two-thirds of the number of (whole) pawns that would normally be required for any given spell or laboratory exercise. Thus if you wish to cast a Ritual spell that would normally require six pawns of Vis (of the Art with which you have the Affinity), you need only use four. This Virtue can never reduce the required amount of Vis to zero.

I'm not sure what the bonus to spells to determine whether the Vis is tainted should be.

I don't think that there are spells that allow you to identify the taint of vis. Generally the first warning sign is when you turn evil, the Divine smites your ass, or Faeries start killing Redcaps since you burned up their friends. I would simply allow the magi to identify tainted vis.

Ah. Okay. Thanks.

I like the idea behind this. It could go well with an Affinity or Puissant Art. Come up with a mechanic for determining the taint and that could work. Actually there is a spell for determining the Realm of an Aura, it probably wouldn't be too much of a stretch to have a Perception + Lore (pick the Realm) roll to determine the taint. I wouldn't have a problem with it.

A realm aligned spell should be able to detect vis aligned with the spell. Sense the Nature of Vis is already attuned for the magic realm. Since the spell is of such a low level (5th), I would just give this spell to the player who took the virtue and it can be cast for all realms as one spell. Keep in mind that you may or may not be able to detect infernal vis, depending on whether the ability for demons to lie extends to things that they create or leave behind, or whether there needs to be an active intelligence to continue the lie. I personally prefer the idea that it requires someone (demon) actually continuing the lie, it seems more vibrant and "mythic" to me that a demon, once creating or getting infernal vis would employ any and all tactics to ensure that it is used...

IIRC there is an explicit note that Infernal Vis can't be checked by hermetic magic. Although having a priest bless it or a Divine Aura might evaporate it.

It might be in RoP:Infernal, which I do not have.
The Limit of the Infernal, on the other hand, says only demons. Personally, I'd prefer only actual named demons be able to lie perfectly to Hermetic magic, and infernally tainted creatures cannot. A diabolist might be able to evade detection of his infernal taint because he is under the aegis of a demon, perhaps. I don't particularly care for the idea that everything infernal, whether intelligent or not, can "lie" to Hermetic magic. My sensibilities want it to be an active intelligence, and RAW from the main rule book says demons, not everything infernal.

I also note core says everything with Infernal might is a demon. Its only RoP: Infernal that starts differentiating types of infernal creatures. Infernists also probably have powers designed to deceive. (They explicitly do if you have RoP: Infernal.)

Infernal Auras are demons?

Those generally don't have infernal might.

So the basis for detection is whether or not something has infernal might?

IIRC vis is magic made material, and respond to it, even if it is from infernal, divine or faerie source, and there isn't any way to change this.

Only if the vis blows up in your face do you have a chance to know if it was tainted, divine or faeric (And if you're a merenita, a chtonic magus or even a holy magus, you may not even notice it). After all, you may suffer a lot of botche dice with vis prada and faeric vis IIRC.

You can detect Faerie Vis:

I can't find anything in Realms of Power:Divine which says you can't detect Divine/Holy Vis, so I'm inclined to think that you can detect it, as well, in the absence of something saying you can't. That leaves Infernal Vis.

Personally, in a game that puts a game contract implicit in character creation (boons and hooks for covenants and Story, and to a lesser extent personality flaws for characters) I, as a player, don't want to play in a saga where the SG can just decide that the Vis my character was working with was infernal. Too bad, so sad, deal. It's much more interesting, as I've said elsewhere, to play a character who chooses the dark path by conscious will, rather than being tricked into it by SG fiat. I can accept, to some degree, that a character might be fooled by a demon, but from a metagame standpoint, that needs to be discussed between player and SG/troupe, because it changes the character of the stories a great deal.

It is.
Vis is Vis is Vis - but some of it is tainted.

Some of it is tainted in a certain way, as to have certain mechanical effects. Among the Infernal types only Vis Sordida ('filthy') comes to my mind. It works as vis does, but IIRC it is more powerful is used to boost spells, if used in devices the effects may be corrupted, and the user gains a new sinful Personality Trait or increases some existing Trait.
And I like this idea. So if I'm SG'ing I sometimes make sure people note certain vis found sometimes, and to inform me if using it. Good players don't use this metaknowledge to have their magi become paranoid, investigate the vis or trade it away to unknowing buyers. And when using it I start them out on a path of darkness, but also promise power, and see if they bite. Most likely not, because I've seldom seen players voluntarily setting up a character to fall to Evil. But it's fun as long as it lasts, possibly resulting in permanent changes to personality, Reputation, or devices with corrupted effects.