The tzitzith-tassels consist of four strings doubled over so that eight strings appear to hang from each corner (Menachoth 39b). There is also an area where a single string is wound around the other seven, consisting of one-third of the tassel (Menachoth 39a). This must be held in place by a knot (Yevamoth 4a, b). The custom is five knots and four areas of winding on each tzitzith-tassel (Targum Yonathan). The prevailing custom is that these wound areas have respectively 7, 8, 11 and 13 windings.
Twist פתיל
Some say that this denotes a single thread made of two strands twisted together (Sifri; Targum Yonathan). According to this, only one of the eight strings would be dyed blue (Yad, Tzitzith 1:6). This was done by dying half of one of the strings before it was inserted (Teshuvoth Ramban, P'er HaDor 21).
A second opinion is that the word pethil here denotes a doubled-over string (Tosafoth, Menachoth 38a, s.v. HaTekheleth, end, 39b, s.v. U'Posle-hah). This may agree with the opinion that an entire thread was dyed blue, so that when it was doubled over, two out of the eight strings were blue (Raavad on Yad, Tzizith 1:6).
There is a third opinion that the word pethil here denotes the thread that is wound around the others (Rashi, Menachoth 39b, s.v. U'Posle'hah; Rashi on Devarim 32,5). Thus, it was the blue thread that was wound around the others. According to this opinion, the number of blue threads is not defined, and may be equal to the number of white threads. There were thus four blue and four white strings in the tassel (Rashi, Tosafoth, Menachoth 38a, s.v. HaTekheleth).
If the special blue wool is not available, the fringes can be made entirely white (Menachoth 38a).
Sky Blue תכלת
(Saadia; Yad, Tzitzith 2:1; Josephus 3:6:4). According to others, it was greenish blue or aquamarine (Rashi; Ibn Ezra; cf. Yerushalmi, Berakhoth 1:5), deep blue, the color of the evening sky (Menachem, quoted in Rashi on BeMidbar 15,38), azure or ultramarine (Radak, Sherashim), or hyacinth blue (Septuagint; cf. Arukh s.v. Teynun). The Talmud states that it resembled indigo (Menachoth 42b).
This blue dye was taken from an animal known as the chilazon (Tosefta, Menachoth 9:6). It is a boneless invertebrate (Yerushalmi, Shabbath 1:3), having a shell that grows with it (Devarim Rabbah 7:11). It is thus identified with a snail of the purpura family (Ravya on Berakhoth 3b; Mossef HeArukh, s.v. Purpura). The Septuagint also occasionally translates tekheleth as oloporphoros, which indicates that it was made from the pure dye of the purpura, this verse, 'dark red.'
There were some who identified the chilazon with the common cuttlefish, Sephia officinalis (Eyn Tekheleth, p. 29), but most evidence contradicts this.
It is known that the ancient Tyrians were skilled in making this sky-blue dye (2 Chronicles 2:6; cf. Ezekiel 27:16), and that the snails from which it was made were found on the coast of northern Israel and Phoenecia (Targum Yonathan on Devarim 33,19; Shabbath 26a; Strabo 16:757). This indicates that it was the famed Tyrian blue. Around the ancient Tyrian dyeworks, shells of Murex trunculus and Murex brandaris are found. These dyes were also made in Greece and Italy, (Ezekiel 27:7, Targum ad loc.; cf. Iliad 4:141; Aristotle, History of Animals 5:15), and remains of these ancient dyeworks have been found in Athens and Pompeii. The shells found there were the Purpura haemastoma and Murex brandaris (cf. Pliny 9:61).
Some have identified the chilazon with Janthina pallia or Janthina bicolor, deep water snails which produce a light violet-blue (hyacinth) dye (Rabbi Yitzchak Isaac HaLevi Herzog; The Dying of Purple in Ancient Israel, Unpublished, 1919). In ancient times, animals such as these were renowned for their dyes (Pliny 9:60,61).
The dye is removed from a cyst near the head of the snail, preferably while the animal is still alive (Shabbath 75a; Aristotle, History of Animals 5:15). It is boiled with alum as a clarifyer (Menachoth 42b, Rashi ad loc.; cf. Rashi, Avodah Zarah 33b) to produce the dye. The wool is then grounded with alkanat root or aloe wood in order for it to take the dye well (Yad, Tzitzith 2:2; Pliny 9:63).
Only a few drops of dye could be obtained from each snail (Pliny 9:61), and according to one modern researcher, over 8000 snails would be needed to make a single cubic centimeter of the dye. This explains its high cost and its restriction to royalty.
