The following description was prepared by William Gross:
Breastplates – ornamental metal plates or shields hung in front of the Torah scroll – are found in all Ashkenazi communities, as well as Italy and Turkey, but designed differently in each community. In most cases the breastplate is made of silver or silver-plated metal. In Italy the breastplate is shaped like a half-coronet and known as the Chatzi-keter, "half-crown." In Turkey, the breastplate is called a Tas, and assumes a variety of shapes – circular, triangular, oval, or even the Star of David. In Western, Central, and Eastern Europe the breastplate is called either Tas or Tziz; its function there is not merely ornamental: it designates which Torah scroll is to be used for the Torah reading on any particular occasion, with interchangeable plaques.
The most notable early breastplates, from 17th-century Germany and Holland, were either square or rectangular, but over time they became rounded and decorative, and bells or small dedicatory plaques were suspended from its lower edge. During this period, the design of breastplates was influenced by that of the Torah Ark and the parokhet (curtain) concealing it, featuring various architectural motifs, the menorah (the seven-branched candelabrum), Moses and Aaron, lions, or Torah crowns.
This is a special sort of Torah shield used in Italy. It was called a "Half Crown" [Chatzi Keter] and was often used to mark the extra Torah scrolls in the order in which they were to be used on holidays. This one is backed by an iron sheet and is marked for the "Sefer Shelishi", the third scroll. In the Moldovan collection is another such shield donated by the same person and dated to 1791/92, placing this one in Ancona of the late 18th century as well. The donating Alconstantini family was an exceptionally prominent and wealthy family of the Jewish community in Ancona who was the major support for the Jewish Community.
Inscription: Crown of the Law Third Scroll Given By the Revered Gentleman the Honorable Rabbi Shimshon, Son of the Honorable Teacher Avraham Alcostantini, May His Rock and Redeemer Protect Him