Interesting Potent Magic options

I like the potent magic virtues, both for flavour and for actual use. They have the same kind of area as magical focuses but unlike them really rely on shape and material bonuses to make them shine. Meaning that to make a good potent magic choice, you need something that is interesting AND supported by useful shape and material bonuses.

What I'd like to do with this thread is to share some good examples of this. I'll start

Necromancy - A classic, also lots of shape and material bonuses for controlling dead people, hurting them and flat necromancy bonuses.

Fire - Quite a few items that give a bonus to mucking around with fire such as lamps, hearths, rubies

Blood - Bloodstones and Rubies both give powerful blood related bonuses and blood is a versatile and creepy choice of theme

Anyone got any good ones?

Wards is the most obvious one

A personal favorite of mine is Potent Magic (Dragons) - Minor Virtue. Emeralds give a +7 bonus for dragon-related shenanigans.
Cinnabar also gives +5 to dragons as well.

Faeries have iron and pan pipes that both contain whopping large bonuses

I like Potent Magic, I've always done so, since I first read it in TMRE. Never used it though. I built a specialist magus with it for a once off. I also tried the aforementioned Dragons theme but I changed magus early in that saga because I grew tired of being overspecialized. I've toyed with it for a character build or two but never 'field tested' it.

Thematically it is cool, but I have a reservation with the way Magic Theory is a limiting factor to how much bonus you can utilize. I mean I don't disagree, it makes sense. And it is not a factor for the lower bonus amounts. But it annoys me that a specialist magus with a high bonus can't use it all. And once he raises his MT he needs to reinvent the spells(s) in new version(s). And that seems a waste of time, especially if you like Mastery which needs to start all over for the new version. Unless I'm grasping the way Potent Magic works all wrong.

I've a character being written up now considering using Potent magic in stone.
There is a fair amount of Terram or stone on the S&M table, so "stone" might be a good one.
Would it also count the types of stone?
Eg. Agate. Bloodstone. Obsidian. Marble?

Just to be a little drunk: a Theban magus with a Potency in the Imperial Purple.

For reference, that's +10 to royalty, +7 to rulership and authority, +5 to control people. It probably indicates that the magus or his parens specializes in Rego Mentem and has political leanings in favor of Greek restoration.

Having a magical potency in a particular material or shape rather than a target for the spells and effects seems like a different virtue (not a bad virtue but a different one)

I don't see why one couldn't have a focus, or thus a potency, in "these effects, which are connected together by a particular shape or material." It's no different, really, from a Potency or Focus in a Planet, for example.

This is just particularly interesting as a Potency because Potent Magic spells would have a go-to material to use for their bonus.