Q: At an ordination Mass, where you really have only three deacons performing some of the actions of the liturgy, why do other deacons wear dalmatics? Shouldn’t they only wear alb and stole?
A: I’ve been looking at the Ordination of Bishops, Priests and Deacons, and at the Ceremonial of Bishops, and I see no indication for how extra deacons are to be vested at such events.
All I can give you is an opinion – that a deacon’s default vesture includes the dalmatic. There is an interesting detail in the revised Order of Celebrating Matrimony for the celebration without Mass. If a deacon presides, he may wear the dalmatic, as an alternative for a priest presider, who may wear a cope (OCM 80). This surprised many of us who thought that the dalmatic was to be used only for Mass. It makes me think that the dalmatic is simply a deacon’s formal wear, and that extra deacons who do not have responsibility for eucharistic ministry still appropriately wear the dalmatic.
But if you ever find something else on this theme, I’d be very interested in seeing it.