Birettas and Zucchetto

It is very critical to comprehend the distinction between these two kinds of liturgical headwear. Biretta is a four or three-cornered cap with a pompon – not always in the same color, while a zucchetto is a spherical skullcap.

The biretta

Biretta is a stiff square hat with three or four rounded ridges used by Roman Catholic, Anglican, and European Lutheran clergy for liturgical and nonliturgical events. Other Christian faiths, such as Anglicans and, more infrequently, Lutherans, have adopted the cap as part of their clerical attire. 

In the Roman Catholic Church, the color indicates the wearer's rank: red for cardinals, purple for bishops, and black for priests, deacons, and seminarians. White is the official color for the Pope, who seldom, if ever, wears this type of headgear. During processions or while seated at Mass, clergy may wear the biretta.

A tassel is usually attached to a biretta. The biretta evolved from the medieval cap known as a birettum, sometimes known as a pileus. It had developed through numerous versions by the 16th century and had virtually reached its current shape.

The zucchetto

The zucchetto is a tiny silk skullcap worn by Roman Catholic clerics. The zucchetto, which evolved from the pileus (q.v.), a close-fitting, brimless hat popular among Romans, has most likely been worn by ecclesiastics since the 13th century. It was invented in the 13th century to hide the tonsure (the piece of a man's hair that is shaved when he enters the clerical stage.)

It was worn beneath the miter and biretta to protect them, and it is still worn beneath these head-coverings at liturgies. At other times, it is worn alone. The color of the zucchetto denotes the status of the wearer. Only the Pope wears white zucchetto; cardinals wear scarlet, bishops and other church leaders of equivalent status wear violet, and lower-ranking priests wear black if they wear them at all.

Conclusion

Cardinals do not wear a tuft or "pom" (they are given their birettas and zucchettos by the Pope, who elevated them in a ceremony known as a consistory – they will form a line and kneel before him when receiving them). Bishops wear a purple pom, priests who have been appointed as prelates to certain positions within the Vatican wear a black biretta with red pom, and diocesan priests and deacons wear. It is sometimes said that seminarians may only wear birettas without pom-poms; however, there appears to be no definitive judgment on this topic.