From a reader:
Is it appropriate to wear an amice, when wearing a cope and surplice?
Under usual circumstances, such as Benediction, the priest or deacon will not use the amice with the surplice and cope.
However, an assistant priest at a Solemn or a Pontifical Mass will use the amice over the surplice before putting on the cope. So would the attendant deacons who would sit on either side of the bishop, handling his miter, etc., but they use the dalmatic.
Here is a photo of the vesting of a bishop before a Pontifical Mass. I was acting as one of the attending deacons and you can see me on the left with the amice over the surplice but before we put on our dalmatics. The second deacon is to the bishop’s left.
Here is a photo from a different Mass. The two attending deacons are standing in their places.