Yesterday one of my players piut forward this question: "if a lacuna (aura 0 area inside a more powerful aura) develops an aura for whatever reasons (sins committed there, powerful magic cast there, a miracle...) does the new aura gets overwhelmed by the surroiunding aura or does it stay at a lower level without problems.
So, a room inside a city (divine aura 3) has a lacuna (aura 0). The room becomes the residence of a Jerbiton for say 30 years and develops a magic aura (magic 1). Does the room now has a magic aura 1 or is it overwhelmed and becomes a divine 3 aura?
First, if there's a "Central Rule" in the Spells chapter*, then there should be one at the start of the Magic chapter: "Magic is unpredictable, or at least not perfectly so." Unless the rules specifically state otherwise (and even then, just to mix things up), don't feel there is only "1 way" things have to work. Ghosts, demons, fae, any loosely defined magical or mystical effect, especially those off the beaten track, have few or no rules that you can't play with to keep things interesting. Magic is not predictable.
(* Modify a spell's level if SG/Troupe think it needs/deserves/demands it, p 111)
This doesn't mean folk can't have an opinion, a preference or a favorite houserule, or that it's wrong to ask in these forums, just that no SG should feel that there is only 1 "right" answer for things like this.
Now, in this case, lacunae do start with an aura of their own, or do so in some cases, that's in the first line of the section on them. (HoH:Soc p 57). They are not always tied to location, or to past events at that location - some move, some disappear. Magic is unpredictable that way.
Magi do not know (much less agree) on how lacunae are formed, they only have partial theories. So, in your example, given a "neutral" lacuna that then overlaps an event that might normally cause a (shift in) Aura, anything could happen to the lacuna...
o it might completely ignore the event
o it might get smaller in area covered
o it might disappear, permanently or for some duration (depending on the triggering event)
o it might begin to fade over a longer time
o it might alternate with the new Aura, predictably or not
o it might change to the newly created Aura
o it might exist as a lesser or greater intensity on it, a sharp variation
o it might, possibly, move (inexplicably, or at least with a very obscure explanation)
o some other, more complex reaction or pattern or response.
What is clear is that a lacuna is not "just an area without an Aura" - it's something different, or can be if the SG wants it to be. I'd have to know you, the Troupe and the current Saga to guess what would make the best story.
But you've got a great hook element asking to be used - unless it's an undesired distraction, weave it into the plot if you can, don't just let it be an unrelated and forgotten blip.
Well, the case was that we were in a city, and we encountered a lacuna area in Dublin. In a prostibule. (Yes, we go to prostibules quite regularly IMS). One of the players (me, actually) started to say how great it was to to finally be in an aura where the penalties for casting spells were not prohibitive and then Jordi pointed out that the adventure was being run by Laura (his GF, my flatmate). That means that the best place to cast spells being the most evil-infested place in town was not casual at all, and that we were about to get a rectal inspection equivalent in short notice. It wasn't that terrible in the end (she was feeling nice) so we only ended up having to battle accusations of devil worship and smashing a succubus (where are the DEO magi when you need them?), all with the magi of Eirean Gate breathing on our necks not to f*uck up their playground (Dublin). However, it sparked the idea (pub discussion after the session) that the room should have an infernal aura since it was a place of almost permanent sin. It was said that then the Divine aura would overpower it unless the infernal was higher. This was why Laura made it into a Lacuna. And so this post was born
(Altho', I tend to think of sex as Divine... meh, you say delicto, I say delicious, whatever... But there's a diff between "sin invested" and "evil infested", I'd submit. RoP:Infernal lists "den of iniquity" as Level 1, and "site of a grisly murder" as level 2, just as starters... Anyway...)
So... the lacuna doesn't actually have a history one way or the other, or at least not as observed by any PC's, so that's a blank slate.
Evil Auras can have "flavours" (erm, maybe not the best choice of words in this instance... ) - can have "tarnishes" toward one sin or another. Clearly, this could be carnal sin, and that would fit fine. But any "sin" is possible in a place with that history! A brothel could certainly have a debauched aura (which would explain the repeated attraction to PC's - grab those confidence points!). But it could be an interesting sideplot if the Aura was found to have a different tarnish, from a different sin...
Or, what if the Lacuna were originally from a different source, and that source still existed? What if that different "sin" were merely echoed in the brothel - below the current building is the long-forgotten site of an ancient pagan temple where sex magic was practiced - Lair of the White Worm, anyone?
Or, it could have been a more "typical"(?) lacuna, created from a great work of art or magical event, and then corrupted over time - but what was that initial spark, and what remains of it?
read the section again (couldn't remember where it was) and it seems that it is right: there can be a magic aura of 2 inside a building in the middle of the Vatican (say, divine 6), and the Divine aura would not suppress the Magic aura: the room would have 0 divine aura and a magic aura of 2. Nice to know for future stories
Lust is a "deadly sin", but a sin only against yourself (and God). "Evil", true Evil, is done against others. The worst glutton in the world is not necessarily "evil" in this sense, no matter how much they eat. I submit that is a significant difference.
It'll be suppressed by the Dominion aura during the day, but, yeah, that'd show up at night. Note that you need a "grisly" murder - ghastly, gruesome, causing horror or dread - to qualify.
In my private canon, anyone with enough (Realm) Lore can figure out how to create a lacuna through what's essentially primitive geomancing, but the arrangement is obvious, since it involves a lot of stuff to counter the dominant aura. A lot of pre-OoH wizards found it convenient to create a desecrated workplace, exchanging the -9 Dominion penalty for the -1 Infernal penalty. (Others employed a form of Entreat the Powers, of course - many wizards are smart enough to figure out that adding Infernal association won't help people get used to them.)
Likewise, in my canon: When it comes to the Order, well, the Artes Liberales were just sitting there, and ambitious Bonisagi have had 400+ years to integrate mysteries into Hermetic Theory. Get Geometry 3 and you can work out how to design a geomancy setup to create a lacuna. Jerbiton magi took that discovery and ran with it, developing no small amount of House lore/techniques based around ordering their environment to perfection.