Chalk was blessed at the Epiphany mass so that we could mark our houses with a blessing for the coming year. Suitable prayers are available from a variety of sources. These are from The Twelve Days of Christmas by Elsa Chaney.
Peace be to this house, and to all who dwell herein.
From the east came the Magi to Bethlehem to adore the Lord; and opening their treasures they offered precious gifts: gold for the great King, incense for the true God, and myrrh in symbol of His burial.
Our Father …
All they from Saba shall come, Bringing gold and frankincense.
O Lord, hear my prayer. And let my cry come to You.
Let us pray. O God, who by the guidance of a star didst on this day manifest Thine only-begotten Son to the Gentiles, mercifully grant that we who know Thee by faith may also attain the vision of Thy glorious majesty. Through Christ our Lord. Amen.
Arise, O Jerusalem, for thy light is come, and the glory of the Lord is risen upon thee—Jesus Christ born of the Virgin Mary. And the Gentiles shall walk in thy light and kings in the splendour of thy rising, and the glory of the Lord has risen upon thee.
Let us pray. Bless, O Lord God almighty, this home, that in it there may be health, purity, the strength of victory, humility, goodness and mercy, the fulfillment of Thy law, the thanksgiving to God the Father and to the Son and to the Holy Spirit. And may this blessing remain upon this home and upon all who dwell herein. Through Christ our Lord. Amen.
After the prayers of the blessing are recited, the initials of the Magi, Caspar, Melchior and Balthasar, are inscribed upon the doors with the blessed chalk. (The initials, C, M, B, can also be interpreted as the Latin phrase Christus mansionem benedicat which means “Christ bless this house”.)