Ghost capturing Jar


I have a necromancer who enjoy collecting ghosts to learn from them later, or ask them about very specific informations.
She wishes to enchant an item - a jar - so that companions and grogs can capture such ghosts when they are adventuring - the necromancer prefering the confort of her lab.

Basically, such jar should have 2 powers, i think, so that would be an invested device:

  1. capture a ghost (or command him to enter the jar)
  2. once the jar is sealed, keep the ghost inside until the jar is open again.

First effect seems possible with a spell of Coerce the Spirit of (Form), most notably "Coerce Ghosts" such as the spell in Legends of Hermes p65. That would be a ReMe 20 effect.
Second effects seems possible with something like the spell "Voices from Hollow Spaces" from HoH: True Lineages (so, a ReMe 35). But this spell makes me wonder about its base effect being level 15 which doesn't correspond to any base effect from core rules. Also, in my case, the range Voice might be useless because first effect would have driven the ghost inside the jar already. So maybe a Touch range would be enough.

But would it be possible to achieve an easier result with a version of Coerce the Spirit of (Form) with a Concentration Duration, and item maintains Concentration?
Maybe something like:
Coerce the Ghost: ReMe 5, Range Voice (+2), Duration Concentration (+1), Item maintains concentration +5 lvl, for an affect lvl 25, to which we add
few more levels for number of uses and Penetration.
That might even be enchanted as a lesser enchantment...

What are your thoughts?

Both could be achieved with a Ward that could be lowered/raised upon command. Altho' the trick for the grogs then would be to get the ghost into the middle of that.

Yes, that's true, but i assume such ward would be a large item, wouldn't it? May i ask how you would design that?