Inexperience mostly , though ArM5 p.84 includes shed skin from a human being as well as excrement. You have to assume at least one of the latter per day and as for the former, humans are shedding skin constantly. In these forums I've seen a few much shorter duration objects considered as ACs including scent and breath.
My point was not that everything we come in contact with is an Arcane Connection, just that there are enough Arcane Connections formed in a day of walking in the forest, say, that trying to catalog and assess them all )in order to become aware of one that has fallen into an enemy's hands is so time-consuming a task as to be impractical. Because of the volume of ACs, there is no practical brute force way to sift through them all. I may be missing something, but that in itself seems sufficient to keep most ACs one-way. at least until they are used.
I know the hair in my hand is an arcane connection to you so I am aware of it and so I can use it. You don't know I have the hair so you can't. Even if you do become aware that I have a hair, you have no way to know it's yours without casting a spell on it (possibly through my parma magica), or by asking me or by snooping around. You also can't destroy it without similar shenanigans.
But the hair is a double-edged sword (sorry if that sounds like a bad mixed metaphor). I can't just go around collecting Arcane Connections to other magi without some risk to myself, besides the risks inherent to breaking the Code. And once I use the hair, you know I have some sort of Arcane Connection to you. IMS we haven't gotten to the stage of determining if that's enough for the target to become aware of the AC. She's aware that there is an AC, but may not know enough about its nature to use it.
I like this approach. Clearly you're going to have situations where a player thinks he has an AC and the SG has to over rule him, but that's life in RPG. For us, what is significant about the connection is awareness. The magus who takes the hair is aware of the AC, the other is not. So far that has been enough.
Here's an example that happened one session. Magus A threatens magus B in writing. The incident blows over eventually and B destroys the written threat. My magus asks why he would do that rather than fixing it in the lab as a permanent AC in case he ever has to go to war with A. Magus B, though, is afraid that by keeping the document it could be used against him, since A is aware of it and aware that it is an Arcane Connection, therefore he can use it against B.
It's important not to confuse modern laboratory and CSI techniques with medieval understanding of things.
I believe that most of the forum examples you refer to were more in the context of "what is and what isn't technically an AC", not "what is and what isn't practical as an AC". Breath, I would suggest, would last for sheer moments - if you don't collect breath as it is expelled, it has already expired. (Scent - that might fall into the "hours" category.)
More to the point, most of what you mention would need to be used "today" (if not "immediately") or be fixed in a lab to avoid expiration - and that would be a challenge in itself, beyond collecting it in the first place.
Well, I'm not likely to adopt your approach, but I'll freely admit that it's clear you've put enough thought into i that it's clear and consistent, and not (particularly) contradictory with any other rules, and that's my first standard for a good houserule.
this thread lost the focus ImhO
The questions was if it is possible to create a jar that blocks ACs. Not if ACs are uni- or bidirectional.
Either way, if I have some container that can block ACs, I also could but in e.g. a book were I know some nasty guy has an AC to it. And obviously I don't want him to affect my precious book.
So please back to the question
True enough, but any real answer to the OP question depends largely on the answer to the question. However, since it was cmjaimet's question, we use his Saga's assumptions and definitions.
So - given the interpretation that AC's are bi-directional (but only if they are "known"), is it possible etc?
I would suggest...
o A ReVi could do it - as a general ward against any/all creatures of X power. This would be much broader in effect, and against magi with high Art scores very expensive. (Applying other Vim Guidelines to ReVi (parallel application is suggested at times), perhaps an advantage in magnitude could be gained if the target of the ReVi were more limited.)
o Using PeVi, one might just make it "appear non-magical" - that seems to fit the bill.
o Use PeVi to "dispel effects of a specific type". I'm not perfectly comfortable with this by the RAW as it assumes a Target not yet sensed/present, but it certainly fits genre and seems the most appropriate TeFo volunteer.
o A MuVi oe PeVi affect on the AC itself, whatever is "in the jar", to make it "appear non-magical" while there. No, there are no direct Guidelines for this - so I'd take a page from InVi and go with the largest spell that would use/detect the AC. The higher the effect, the better the protection.
(There are certainly drawlbacks to the "An AC is a Part of a larger Whole" interpretation, and the subsequent "one-way only" corollary*. But the whole "knowledge" thing is so subjective - what is the diff between "suspecting" and "strongly suspecting" and "being sure" (but perhaps wrong?) and actually "knowing"? In my life I've "known" things that turned out to be dead wrong - what then?
(* I believe the Mage-Familiar symmetry is noted specifically because it does not follow this expected pattern.)
If one loses the whole CSI/Gattaca level of AC's floating around, then with few exceptions an AC must be intentionally gathered and cannot simply be "recovered", say, after a Target walks down a road. If AC's were that easy to leave floating around behind you, the very first spells every apprentice would learn would be a series of Perdo effects to constantly destroy such - more valuable than Parma to any mage.
IMS it's down to the GM's discretion. He tells us when we're "aware" enough of the Arcane Connection to use it. So, it's a combination of correctness (the GM is all-knowing), certainty by the magus (highly subjective sometimes), and details known about the AC by the magus (also subjective).
That was one of my first concerns when we started playing. As I've mentioned elsewhere, this is my first saga. My GM has been playing for twenty years (in earlier versions), so we mostly follow him. So far the rules for ACs are working but I can see from this discussions some holes that could be exploited by unscrupulous magi. In addition to Perdo spells, a new magus would also want Intellego spells to locate ACs that passing magi might drop.
I do like the idea that ACs are double edged swords and should be treated with care, though.