The use of holy oil is a very ancient tradition, as is the method for keeping it.   Holy Oils were used in the Old Testament for the consecration of priests and kings, as well as for the ordination of Levites.   It was also used during purifications and consecration of altar.

Holy oils fall into two main categories: Oil for the Sick and Chrism.   According to tradition, the use of Oil for the Sick stems from scripture, where it is recorded that Saint James directed the community to pray for the sick and anoint them with oil in the name of Jesus.

In the Western and Eastern churches, priests retained the right to bless the oil for the sick.

In some cases the oil may even be blessed in the home of the ill person.

Chrism stems from the Greek word chrisma, and referred to substances that were used for anointing, but the word came to be reserved for this oil that was used in religious ceremonies, especially Baptism and Confirmation.

It appears in early patristic writings, and it is still debated whether the use of chrism stems from Christ himself or is of ecclesiastical origin.  Chrism is a mixture of oil of olives and balsam.

Olive oil is the main ingredient, and had been so throughout the Torah, mentioned specifically in Exodus, Leviticus and Deuteronomy - based on this scriptural authority the Christian tradition also adopted the use of olive oil.

Balsam is an aromatic resin extracted from the terebinthine family of trees and plants, and is a required ingredient in chrism.

According to early patristic writers and theologians, a bishop must bless the oil, usually during Mass on Maundy Thursday, where it is placed upon the altar to be blessed with the bread and wine.

In the Roman rite, the balsam and the olive oil are blessed separately and then mixed.

After the ceremony, the chrism is distributed among the priests, who take it in a silver vessel called an oil stock, a vessel designed and used only for holding holy oils.

This practice of preserving the oils in a metal bottle or jar goes back to the 6th century.

The oil stock is kept locked in an ambry or box affixed to the wall of the sanctuary.

Here at Trinity, this ambry is located in the Saint Nicholas Chapel.

The vessels are differentiated by initials etched on the outside of them.   The vessel holding the holy chrism is labeled SC (sanctum chrisma), that holding the oil of the sick is labeled IO, (oleum infirmorum) and the oil of catechumens is labeled OC or OS (oleum catechumenorum or oleum sanctum).

At Baptisms we commonly move the chrism (SC), close to the font so it is easily accessible during the rite.

For sick calls the oil of the sick is carried in the oil stock to the person to be anointed.

Traditionally, after Maundy Thursday of each year the unused portions are to be burned in the sanctuary lamp or poured into the earth.