From a reader…
When a priest vests as a deacon at High Mass, does he wear the stole as a deacon would under the dalmatic? Or as a priest?
I happened to notice a priest wearing it as a deacon, and, despite being vested in the dalmatic, it struck me as odd.
I assume that you are talking about the Extraordinary Form, because you won’t see priests as deacons in the Ordinary Form. Also I assume you are talking about a Solemn Mass. Sometimes “High Mass” is used interchangeably with “Sung Mass”. Solemn Masses have deacon and subdeacon.
When a priest takes the role of deacon in the Extraordinary Form, he vests as a deacon and does those things the deacon would do as a deacon does them. Father is still a deacon, though he is also a priest. When Father vests as a subdeacon, he does not wear a stole at all. Nor would a deacon who takes the part of subdeacon.