A prosphora is made of flour, water, salt and yeast, and of nothing else. It is shaped in two layers pressed together, which are commonly explained as the two natures of Christ, and the top is impressed before baking with a carved wooden seal. The central square of the seal carries four abbreviations arranged around a cross: the first and last letters of Jesus and of Christ in Greek, and the Greek word meaning conquers. Around that square the seal usually carries smaller devices for the Mother of God and for the saints.
The preparation happens before the liturgy proper begins, at a side table in the sanctuary, and it is a service in its own right with its own prayers. The priest cuts the stamped square out of the loaf with a small lance shaped knife, and that piece, called the Lamb, is the only bread that will be consecrated. He then cuts a triangular particle in honour of the Mother of God and places it to the right of the Lamb, nine particles for the ranks of the saints to the left, and further particles for the bishop, the clergy, the living and the departed, each name read from the lists the congregation has handed in with its loaves. The particles are arranged on the diskos around the Lamb, so that the paten carries a small picture of the entire church, in heaven and on earth, gathered about Christ. After the communion those particles are put into the chalice.
Everything left of the loaf is cut into pieces and set aside. It has been touched by the offering and blessed with it but it is not the sacrament, and it becomes the antidoron given out to everyone at the end.