The Papal sphragistics mainly distinguishes two habits in document sealing: the use of the plumb bull (on rare occasions gold) on one hand and the wax seal or anulus piscatoris on the other. The former had a pendant seal and the second an adherent one.

The bull was attached to both important solemn privileges and to the simplest mandates and letters, and it was one of the most important diplomatic features in papal documents. From an iconographic point of view the bulls of the Roman popes, starting with Pasquale II (1099-1118) maintained a formal identity that has remained unchanged until current day. This expressive rigour, with the obvious variations due to the artistic style of the time, expresses the wish to use a permanent image to transmit the continuity of the Church over the centuries. The two faces of the bull have the heads of Peter and Paul on the rear with the writing: S(anctus)PE(trus)/S(anctus)PA(aulus) and on the front the name of the Pope, his title and ordinal succession number. The apostles’ faces are plastically characterized, with flowing hair and beard for St. Paul and short curly beard for St. Peter. Before Pope Pasquale II the iconography underwent various changes, from simple onomastic types through to more articulated features. From a technical point of view, the bull was made by impressing a round lead circle with metal matrixes that were mounted on a pair of callipers, which were gradually replaced with much larger clamps.

When the lead was pressed it was flattened and the figure was impressed, and the hanging thread was buried into it which had been previously passed through a hole in the lead circle.

When each Pope died, the matrix with his name was destroyed while the one with the apostles’ faces was used again by his successor, and only replaced if it was damaged in any way. Whenever a newly elected pope needed to draw up any documents in the period between his election and crowning, he used the so-called dimidia bull, i.e. a bull with just the apostles’ heads impressed on one side, with the other side smooth. This was because only after the Pope had been crowned and had taken on his Papal name did he order it to be engraved on the matrix. This custom is described in a special formula in the eschatology of the documents.

The red wax seal protected by a small parchment plait or small tin caskets was the so-called annulus piscatoris. Together with other diplomatic elements, this impression identifies a certain category of documents issued by the Papal chancellery, the briefs. This oval seal was very small (between 2 and 3 cm for each axis): it was fixed to the document by two cuts in the writing support that a small strip of parchment was also passed through. The iconographic detail of the fisherman’s rings show St. Peter in a boat drawing in the net, and has the key with the Pope’s name and ordinal succession number. The wax seal is mentioned in the document datary with the formula: … sub anulo piscatoris or  … sub anulo fluctuantis naviculae … The Pope could also place his private (or secret) seal on certain types of letters, i.e. a simple wax seal without any precise details, showing his noble arms.

From the second half of the 19th century, the Papal seal on documents was replaced by a stamp, the modern heir of sphragistics, which reproduces their image, although the Papal bull is still used on very important documents.