While discussing the topic of ritual impurity, the Gemara relates:
When Rav Dimi came from Eretz Yisrael to Babylonia, he said that Rabbi Yoḥanan said: From where is it derived that a woven fabric of any size can become ritually impure? It is derived from the frontplate [tzitz] of the High Priest, which is considered a vessel despite its small size.
Abayye said to him: And is the frontplate a woven fabric? Wasn’t it taught in a baraita: The frontplate is made like a kind of smooth plate of gold, and its width is two fingerbreadths, and it encircles the forehead from ear to ear. And on it is written in two lines: Yod heh, i.e., the Tetragrammaton, above, and kodesh lamed, i.e., sacred to, below. Thus, the words: Sacred to God, were written on the frontplate. In deference to the name of God, it would be written on the top line, and the words: Sacred to, on the line below.
And Rabbi Eliezer, son of Rabbi Yosei, said: I saw it in the Caesar’s treasury in the city of Rome and Sacred to God was written on one line. In any case, since the frontplate is a gold plate, how can it serve as a source for ritual impurity in fabrics?
The frontplate was attached to the forehead of the high priest by a sky blue ribbon. The commentaries disagree whether one or more ribbons were used.
Some explain that since the frontplate was a gold band attached with a thread to a woven fabric, the fabric was considered part of the frontplate. Therefore, it was possible to derive the legal status of the fabric from that of the frontplate and certainly to derive the status of an article made of fabric and metal. The Gemara rejects these possibilities since it was ascertained from the language of the tanna’im that the frontplate was primarily the metal part alone (Pnei Yehoshua).