Mastering Ritual spells without books

I was looking at the rules for spell mastery, and trying to figure out whether one can actually master a ritual spell by practice. The book says that one can spend a seasons asting a spell to gain 5 xp in mastery. The book also says that one can gain mastery in formulaic or ritual spells.
Sure, there can be books on spell mastery. Really nice. But...
Somehow, someone had to learn spell mastery of rituals spells without a book in order for there to be a book.
But to repeatedly cast a ritual spell for a season would seem to
a) require a large amount of expended vis
b) almost certainly have many botches.

So it seems that if ritual spells can be practiced for mastery, the practice is something different.
Which is fine, if that is the case.

So the question is whether, without expending vis, one can spend a season learning mastery of a ritual spell. If so, what is the in-game description of what you are doing for that season?

By the rules as written, you can.

As for what you're doing? IMO you're casting the ritual without any Vis. Nothing happens, because there's no Vis to power it, but you can still go through all the motion.

I see nothing wrong with practicing some or all of a ritual without actually performing it. I practiced my wedding (rehearsal), but only got married once. My actual wedding was so magical veritable rooks of vis must have been involved!

Yes, you can master a ritual spell by practicing. That's explicit. The bigger question is if practice requires vis in the case of ritual spells.

AFAICT, this isn't explained anywhere, but it is something of a challenge to the setting that someone would take on the risk (and expense) multiple times in a season to master a spell to get a reduction in risk in the future. So, just for it to make sense within the setting and the game one must be able to practice ritual spells without risk and, therefore without vis and their attendant botch dice. It's an inference, granted.

In game, you are working out the ritual, setting the timing of your chants, arranging your vis in specific order to be consumed in the casting, working out the astrological timings (artes liberales) and coordinating it to natural magic patterns associated with the aura. You are probably even powering it with your own innate magic, but it never lasts more than a moment because of the lack of vis, but it is enough because it provides feedback to measure your results and continue towards deeper understanding.

Thanks. That is what seemed sensible, but I have been sufficiently confused on other points that I wanted to make sure.