Ritual Magic is risky. A casting roll for Ritual Magic is never cast in a relaxed manner due to the amount of power in play. However, to not have ridiculous levels of botch risk in play, there are two methods for working Ritual Magic.
The errata on Muto Vim, means that Wizard's Communion affecting a ritual spell must be as long as the duration of the spell casting, which is greater than momentary or diameter. I'm ruling D: Concentration doesn't work with Wizard's Communion in rituals, so it must be D:Sun to affect a ritual spell, which we will call Ritual Communion to differentiate it from Wizard's Communion. Those with Mercurian Magic learn Ritual Communion at the indicated level. Ritual Communion, with the longer duration provides 2 magnitudes less for the calculation to determine spell level/penetration outlined in Wizard's Communion. Ritual Communion 30 counts as a 4th magnitude spell.
The Path of Experience
This is the traditional path, of spell mastery and the Golden Cord to mitigate the risk of botching any spell, which also applies to Ritual Magic. It seems reasonable that a magus with advanced experience should have multiple tricks to minimize botching.
The Path of Time
In this path, one may exchange a season of advancement/activity and can negate up to 7 botch dice. The time is spent aligning all of the elements of the ritual, preparing the mind, tuning the mystical energies necessary to cast the spell, investigate vis for its suitability to the ritual, perhaps trading it out for more optimized pawns of vis with the Redcaps. 7 botch dice, coincidentally aligns with the most common version of Aegis of the Hearth used in the Order, the 6th magnitude version, which has 6 botch dice coming from vis and 1 from the base casting roll. The Path of Time can also be combined with Spell Mastery and the Golden Cord to further reduce the risk of botching on even more powerful rituals. One additional advantage to the Path of Time, is that for spells which need a Wizard's Communion to be cast at all, or with sufficient Penetration (see below), is that it negates all risk of botching the Wizard's Communion spell, because it is presumed to be part of the overall ritual of the spell, which was worked through during the season time leading up to the ritual.
Vis in spell Casting
Using vis is always a risky endeavor. A careful reading in the vis section of the core rule book provides contradictory rules, though. Using vis always adds a botch die for each pawn of vis used. It can never be relaxed, and spell mastery only removes 1 botch die per level of spell mastery.
The rules state that one may use a stress die to cast spells, if they have mastered a spell and are in relaxed situations, in order to get a chance at an exploding die roll. This is fine, however, one is never relaxed when working on a Monte Carlo situation, to cast a spell until they get a desired exploding die roll. Casting a spell more than 3 times in a row will result in all subsequent attempts at casting being in a stressful situation, with full risks of botching. After 9 times casting, each subsequent casting will incur an additional botch die. (If you can't tell, I hate the premise of the Monte Carlo simulation available within the RAW).