Handbook of Liturgical Practice of the Russian Church Abroad
Deacons are likewise fully vested before the beginning of the Proskomedia and serve thusly.
Head coverings (kamilavka, klobuk, etc.) are not worn during the Proskomedia at any point, but are donned only at its completion, before the beginning of the Divine Liturgy. If a Priest returns to the table of oblation during the Hours or at various points in the first part of the Liturgy, to make additional commemorations, his head covering is always removed as he approaches the table of oblation and remains off while he makes the commemorations; then the head covering is returned to his head before he re-approaches the Holy Table.