All priests are permitted to wear the zucchetto. However, its use is entirely optional. It can be worn with choir, pian and daily dress. For all priests it’s made of black silk and lined depending on ecclesiastical rank: for Prelate Superiors of the dicasteries of the Holy See and for Protonotaries Apostolic supra numerum lined in amaranth red silk; for Prelates of Honour of His Holiness and Chaplains of His Holiness lined in purple silk; for all other priests lined in black silk. All this is laid down in Per instructionem a circular letter of the Congregation for the Clergy issued 30th October 1970.