On the celebrants rubrics for the Gloria in Excelsis, from Ritual Notes

When the Gloria in Excelsis is said: “A simple rule by which to remember is, that the Gloria is always said in white and red Masses…; and it is said on all green Sundays.”

“While reciting the Gloria the celebrant makes a deep bow of the head five times, i.e. at the word God in the beginning; and at we worship thee; we give thanks unto thee; Jesu Christ; and receive our prayer.  At the end he make the sign of the cross upon himself at the words art most high…”

When the Gloria in Excelsis is not said: “In any Mass celebrated in purple vestments, therefore not on the Sundays in Advent and from Septuagesima to Palm Sunday, inclusive; …It is not said on the ferias of Epiphany-tide nor of the Trinity season when the vestments are green…”

(Ritual Notes: A Comprehensive Guide to the Rites and Ceremonies of the Book of Common Prayer of the English Church, 8th ed., Henry Cairncross, E.C.R. Lamburn, G.A.C. Whatton [London: W. Knott & Son Ltd., 1935], 51-52).