I wonder if I am overly creative here. I cannot see anything in the rules which unambiguously forbids it. Have I missed something?
Say, you want to block a doorway or a cave entrace. CrTe base 3 creates stone, with touch/ring/circle it is level 10. Can you draw a ring around the entrance to block it completely with stone with CrTe10 spell? It would last until somebody finds and destroys the ring (or less likely move the magically created stone out of the ring).
On a similar account, I was considering a CrIm effect to only appear as the above, but without the material effect. Or even PeIm to render the hole invisible, but that adds a second question of whether holes exist and have an image which can be destroyed.
Could you explain your reasoning?
The base individual for stone is one cubic pace, so if the opening is two square paces (18 square feet), it suffices to make the block have a pace thick (1½ foot), so the amount of stone is not the limitation here. Creating just a stone, at touch/sun/ind (same level), is quite a sizeable boulder, enough to block many entrances that need blocking.
As callen correctly points out Creo only works with T:Ind and T:Group when "making" stuff (I believe there's a counterexample in some book, but I'd treat it as an editorial mistake). However, nothing says that it cannot work with D:Ring. Base Individual for stone is a cubic pace, which is enough to wall a reasonably large passage.
CrIm works even better, because it can create the illusion of an extremely thin, and thus large, portion of wall. Not to mention that it base level is lower.
PeIm cannot make the hole invisible, however. The hole is absence of something, so it cannot be targeted.
On the other hand ReIm, albeit less efficient than CrIm level-wise, can accomplish almost the same trick by moving into view the image of a portion of rock that is elsewhere (ideally out of sight). And you can use it with T:Circle!
Similarly, MuIm can make a little pebble look like a gigantic boulder blocking the passageway; and like ReIm, it works with T:Circle.
Are we talking about a circle on the ground inside the opening? Or a circle on the wall around the opening?
If we are talking about a ring on the ground, I think we agree ... it is mainly about the diameter, and taking other posts into account, ring duration is ok, but target has to be individual. Fine.
In my original post, I tried to specify the idea of drawing a ring on the wall around the opening. Nobody has commented on it. Whether it is because it is kosher, or because it went unnoticed, I don't know ... à priori I did not think of any reason why a ring would not apply equally well on a vertical surface as on a horizontal one, but now I see a different problem raised. The circle is only a 2D structure. How does it extend to a 3D target? Obviously, people standing on the ground withing the ring are affect. But is the flying crow familiar affected? I always thought yes. Isn't the ring just describing the base of the cylinder describing the target. Is the scout sitting on a branch in a tree above the ring affected? Drawing the cylinder on a vertical surface, the cylinder described can break game balance, but maybe this was always a problem. I don't think the circle target was supposed to be able to target the clouds. What on Earth does circle/ring really mean, when they do affect more than the soles of the feet of those inside.
I will openly admit the idea of drawing the 'ring' on the wall never really entered my mind. I see how you tried to define that, looking at it in post.
Anyway, I can't see any examples or definitions of D: Ring that are designed or allow for rings as a surrounding-wall or similar scenario. Does anyone else know of examples using vertical or rotating rings? Either way, you're going to need a circular opening for the wall to even try, then it depends if Ring-walls are allowed. Anyone know of any examples?
HoH:TL p.140 has Tremere inscribe Rings on mirrors to trap ghosts therein. Technically, they could be "horizontal" mirrors, but somehow I've never pictured them that way. MoH p.124 has Rings inscribed on book pages; they support illusions (Imaginem effects) of indefinite duration.
My brain is wrapping around several aspects of this- from one sentence in the RAW- a ring duration lasts until the target moves outside the circle or the circle is broken. Nothing in that says that the circle must be cast with the target originally in the circle. In theory if the target is outside the ring then it would have to enter then exit to break the duration. Or of course break the ring.
It does say that it has a maximum range of touch, which means that clouds or anything else you cannot touch cannot be affected. At the same time it makes the effectiveness of large circles potentially problematic, since unless that target is the circle you have to keep touching the target while you draw the circle...
Out of curiosity, is there any evidence of what 'inside the ring' is compared to 'outside the ring'? Is the ring cylindrical? Spherical? If I cast a Ring ward to trap a bird, can it fly up to the heavens? If I cast a massive ring spell to trap a cloud, does it keep the cloud trapped above the ring pretend I want a raincloud always above my magi's tower).
If rings are Cylindrical, how does that affect a Ring drawn on the wall? Does it create a massive cylindrical column of ward? Man, I'm getting weird ideas from this.
I don't think there's a general rule stated anywhere explicitly, but some of the "Ward Against the Faeries of the (Form)" spells make reference to the ring appearing as a (colour) dome. I think that's a sensible general approach, in the absence of anyone finding anything conflicting.
I've assumed the default volume is "full sphere" - ie, if it's on a wall, then by default the circle will affect both sides of the wall. However, as most circles are on the ground, it's usually a moot point. Also, the caster can choose to change the volume to cylinder (using up to the full volume, with whatever percentage of the cylinder above or below the circle), or half-sphere (using 1/2 the volume) if they so choose. Basically "any reasonable shape they actually want, as long as it's related to the bounding circle, and doesn't have more volume than the default sphere.
My inner mathematician knows how to totally abuse this, but I'm sure the writers didn't intend things how I could skew them.
I would tend to agree with Salutor here. I don't tend to have it be spherical, though, as I like the idea of a trapped demon walking up to the edge of a circle to tempt its summoner; bumping its head as it tries to do so just doesn't fit the style I like (good for something comedic, though). So the domes I envision tend to be more like 1st quadrants of negative quartics or similar with +j (y-axis) shifts and then rotated about the y-axis, the x-z plane being the surface on which the circle is drawn. (Sorry if that's too mathematical.)
I like this answer, but it does ruin my plans for a Ring carved on a cliff to summon a bridge.
The other idea I had... non-floor Rings still are vertical in definition, so D:Ring spell to trap a ghost in a mirror literally only encompasses the mirror's planar surface, unless it's laid down.. My friend liked the definition of them being adhered to the surface of the wall or page, or whatever non-ground surface you made. Spherical or sphere-ish seems best though.