Question re: Ritual Magic

[Kelly Pedersen]

Originally Posted by Faolyn

The focus would be an item with the appropriate Gadget limitations,

First of all, how common are these focuses? Are we talking "To use spells of the Plant college, you must have a staff blessed by the Plant God personally", or "To use the Plant College, you must have an oak staff"? Because the Gadget limitations are only for the former. Gadgets must be objects that are rare, if not unique, in the campaign world. Basic explicitly states that Gadgets must be "items [that] are not for sale at any price in the game world." (Emphasis in original).
If the focus items are fairly easy to replace, then they warrant, at best, a -10% limitation if they're big, bulky, and hard to carry around. If they're easy to carry, they're -5%.

Originally Posted by Faolyn

but does the limitation go off the cost of Power Investiture, or the cost of the various Ritual Magic college skills, or what?

Limitations are never applied to skills.
Applying the limitation to Power Investiture means that it affects the bonuses Power Investiture provides. So, for example, if a witch has a spell that has no Power Investiture prerequisite to cast, then they could still cast it even if they lacked the focus - they just wouldn't get the bonus of their Power Investiture to skill.
If you want the actual spells to be limited to casting with a focus, you can just stipulate that that's how the ritual magic works in your world. The game supports this quite easily, no need to limit the skills.

Originally Posted by Faolyn

Also, I'm using other limitations such as Time Required, would these go off Power Investiture as well?

Again, if you limit Power Investiture, you only limit the bonuses it provides. It won't limit the spells themselves. So if you have Preparation Required: 1 minute on Power Investiture, the witch will have to pray, chant, or whatever for a minute to get the bonus that Power Investiture provides, but if they have any spells that could be cast without Power Investiture, they can still cast them. Also, don't forget that Preparation Required applies every time you use the limited advantage. So if you put a 1 minute prep time on Power Investiture, a witch would need to spend a minute preparing for every spell.

If you just want to extend the length of time that it takes to cast spells, just arbitrarily extend the casting time. GURPS Thaumatology has lots of suggestions and advice for altering the parameters of spells - if you don't have it, I suggest you pick it up.