A quick spell to momentarily clean all the gear worn by a combatant.
Immaculate Handiwork of the Squire
Rego Animal, Corpus, Herbam, Terram 20, R: Touch, D: Momentary, T: Group
The equipment and clothing of the individual touched is spotlessly cleaned. Highly complex equipment or disastrously filthy equipment may require a finesse check, subject to troupe considerations.
(Base 4, +1 Touch, +2 Group, +1 size increase to a hundred parts and components)
The base 4 in Rego Herbam is used in Ablure Magica (from Covenants p. 52), which seems a reasonable starting point.
All the other new spells for Ars Magica can be found here.