The general colour of the old bulls is bluish grey, but younger bulls and cows are browner.
Those documents in which the pope speaks in his own name (bulls, briefs, encyclicals, &c.) even when he does not sign them, as we shall see.
The bull, so called from the leaden seal (bulla), is written on thick parchment; the special writing known as Lombard, which used to be used for bulls, was abolished by Leo XIII., and the leaden seal reserved for the more important letters; on the others it has been replaced by a rest ink stamp bearing both the emblems represented on the leaden seal: the two heads, face to face, of St Peter and St Paul, and the name of the reigning pope.
Bulls are written in the name of the pope, who styles himself "(Pius) Episcopus servus servorum Dei; (Pius), bishop, servant of the servants of God."
It is practically only bulls of canonization which are signed by the pope and all the cardinals present in Rome; the signature of the pope is then "(Pius) Episcopus Ecclesiae catholicae," while his ordinary signature bears only his name and number, "Pius PP. X."