I appreciated your comments on the Dalmatic. It has always been my understanding that the dalmatic is a Eucharistic garment, worn by the deacon when serving at a Eucharistic celebration (with the possibility of wearing it for a wedding outside Mass). So, a deacon would NOT wear a dalmatic on Good Friday as it is not a Eucharistic service.
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The Ceremonial of Bishops says in 316 that the bishop and the deacons wear “red Mass vestments” for Good Friday. Even without a bishop, then, the deacon may wear a dalmatic on Good Friday.