[size=150]Vis cultivation[/size]
Breakthrough: High-end major
Details:
This breakthrough would allow a magus to study the effect of warping on the environment and, subsequently, carefully control it through trial and error until enough magical effect has happened as to form a permanent source of magical vis.
This is represented through a hermetic ability, Vis Cultivation, that comes from a major virtue.
To cultivate vis, the magus spends time with a plant, drip of water, icicle, or anything else that will regularly form every year (or every other/few years). This has to be natural, it cannot already be forming vis, or be from an inherently magical source (though he can create it himself, such as planting a seed or rerouting water so as to form icicles in winter). He aplies magic to it so as to gather up warping, working the hermetic ability until the cultivation yields vis on a regular basis.
Just what vis is formed is, of course, based on the phenomena. A tree might make herbam vis, icicles would make aquam, etc. If the source is ambiguous enough, the story guide can decide on the final outcome. Some sources can take longer before they can be worked on (like a fruit tree) while others can be done in a day (like a drip of water). Others can only be worked on in certain seasons (like icicles only during winter).
This requires at least a single pawn of vim vis be used.
Vis cultivation total: Intelligence + Vis Cultivation + Aura + 3 for every pawn of extra vim vis used
The first pawn, the necessity, does not add to the cultivation total, but subsequent pawns of vis do.
Breakthrough idea 1
Yearly vis yield: Vis cultivation total / 10, round up. Takes 1 season of work.
This number goes up by three for every additional yield year. So on a cultivation total of 14, the normal yield would be 2 every year. Letting the cultivation take an additional year would be 5 every two years. Adding another year would be 8 every three years. The yield is capped by the magus' Vim art multiplied by 2. The vis cannot be harvested until the allocated year, and the vis source cannot be worked on again until the magic has dissipated (see below).
Breakthrough idea 2
Yearly vis yield: Vis cultivation total / 10, round up. Takes 1 season of work basic.
This number goes up by 1 for every additional season spent cultivating the vis source. So on a cultivation total of 14, the normal yield would be 2 every year. Spending an additional season of work on the cultivation would bring it to 3 every year. Three seasons would bring it to 4 every year, etc etc. The yield has a cap based on the magus' Vim art during the initial season of work (even if he learns vim in subsequent seasons). Once the magus stops working on it for even 1 season, the vis source can no longer be modified with this mystery except through natural warping and time, as normal vis is inclined to be.
Regardless, the vis source, created like this, is not permanent by default. It will last a number of years equal to the magus' vim score at the time of creating the vis source before the magic dissipates. A ritual spell can be invented or learned after learning this ability that allows the vis source to set and last longer, while another ritual allows the vis source to become permanent (so long as the naturally forming source is not destroyed, damaged or overharvested. A tree that makes vis-like fruit that gets uprooted or set on fire will no longer make vis, after all.)
Creo Vim 20 (base 3, Touch, Momentary, Individual, ritual): Blesses a vis source, such as a tree, icicle, or other naturally forming phenomena, to last longer. This adds the magus' Vim score to the number of years remaining. It can only be applied once every year. Doing it more than once per year does increase the number of years the source lasts accordingly, but it also reduces the amount of vis it yields permanently by 1 for subsequent castings.
Creo Vim X (base general, touch, momentary, individual, ritual): For every magnitude in the base, one vis of the source is made permanent so long as the natural phenomenon continues to grow. For example, a ritual of level 30 would allow 5 vis in the source to remain permanent (base 25, +1 touch).
Making vis sources can be especially risky, as other covenants and magi will most likely become interested in the magic, and it may attract the attention of magical creatures who will desire it for themselves, or perhaps offer in trade.
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Thoughts and opinions?
EDIT: a bit of a tweak