Discovering vis sources

How do magi figure out some of the more "involved" vis sources?
In the saga I normally play in, the magi have discovered that mushrooms harvested the morning after a faerie dance under a new moon contain vis. Pretty straightforward and easy to detect.
What about the Im vis produced by brewing a tea using water from a particular well and the leaves of the herbs in a particular garden, both collected under a full moon? Is the vis apparent in the leaves with an InVi spell before they are harvested? Is there something special about the well?
How are the processes for extracting vis from seemingly mundane items discovered?

We actually had a good discussion of this topic not so long ago. That thread can be found here.

Generally, I think it comes down to local folklore and experimentation. In the case of your example, perhaps there is a local tale of a faerie princess gathering herbs from that garden and water from that well under a full moon to mix up a magic potion. The magi repeat the process and discover it produces vis.

Thanks, Lucius. I missed that post. :blush:

Don't feel bad, the thread title isn't exactly descriptive of the content. Took me a while to find it again. :slight_smile: