Was Woad the dye that was used by Ancient Israel for tekheleth? There are facts scattered around and if gathered together the original tekheleth can be identified. Six candidates have been put forward to be the true or acceptable tekheleth. Do any meet all of the different criteria that various Jewish groups have specified?

Candidates for tekheleth that have been put forth in the last 100 or so years are;

1. Woad or Isatis Tinctoria, a plant producing indigo, which gives a deep  sky blue, (1).

2. Indigo or Indigofera Tinctoria, a plant producing indigo, which gives shades from sky blue to a dark, midnight blue. It is referred to as Kela Ilan by early rabbi's, (2).

3. Spirulina, a blue-green algae, which gives a blue-green to navy blue. It is currently accepted by some rabbi's as an alternative for vegetarians not wanting to use an animal source. Apparently clean colours can not be obtained when gathering it from a naturally occurring water source and it has to be produced in a lab, (3).

4. Cuttlefish, or Sepia Officinalas, a mollusk and put forth as the 'Chilazon', which gives a dark, medium blue, with green overtones. It's blood's reaction to iron filings is used to make a blue dye. It was discovered that any blood could be used to produce this dye. This is the 'Radzin Tekhelet', (4,5,16).

5. Janthina, or the Common Purple Snail and put forth as the 'Chilazon', which gives a colour that has not been disclosed. A claim was made in 2002 that a dye was obtained from the extract of the Janthina, but this has not been substantiated, (6,7).

6. Murex Trunculus, a sea snail producing indigo and put forth as the 'Chilazon', which gives a deep, sky blue.  It is a chemically identical dye to Woad, see here, plus Indigo, which itself was also known as Kela-ilan.  It is currently accepted by Rabbinical authorities as the source for tekhelet dye. It was first named in 1913, as the most likely candidate. However they were unable to produce a consistent blue, instead of purple, until 1980, when it was discovered that exposure to sunlight brought consistent blues. This is the 'Ptil Tekelet', (8,9).

I have made a page to show the colours of the Radzin's Cuttlefish dye, Ptil's Murex Snail's dye, Woad's dye and Indigo's dye, here. 

Woad, or Isatis Tinctoria, was available and is native to Western Asia, including Egypt, the Arabian Peninsula and Israel. It is a hardy, prolific plant, which has been also known as the 'Asp of Jerusalem', (1).  Woad would have been readily available for the ancient Israelites, both in learning how to use it while slaves in Egypt, where is was used, and while travelling through the Wilderness and later living in Israel, (18).

Indigo, or Indigofera Tinctoria, is native to tropical climates and was not available to the Mediterranean area until Greek and Roman times when India became a big producer and exporter, (2).  Indigo, therefore, was not available to the ancient Israelites.

Spirulina is blue-green algae, occurring in tropical and subtropical lakes with a high PH (alkaline) and having high concentrations of carbonate and bicarbonate, (10). This could possibly be found in the ancient Israelites' Wilderness, if they encountered these ponds where Spirulina grows.

Cuttlefish, or Sepia Officinalas can be found in the Mediterranean Sea, (4). However, the Ancient Israelites were not by the sea when the tekhelet mitzwah was given and the first Mishkan built.

Janthina, or the Common Purple Snail, are in tropical and temperate seas and therefore possibly in the Mediterranean Sea, (5). Again, the Ancient Israelites were not by the sea when the tekhelet mitzwah was given and the first Mishkan built.

Murex Trunculus, a sea snail, lives in the Mediterranean Sea, (6). Yet again the Ancient Israelites were not by the sea when the tekhelet mitzwah was given and the first Mishkan built. 

Update!:  New information has come to light that it would not have even been possible for the Murex snail dye to have been converted from purple to blue until the discovery of clear glass in 100AD.  The P'til Foundation knows this.  I have a whole page explaining this, see here 

The Torah states the following regarding the tamei or uncleanness of the creatures that some of the tekhelet dyes are being made of:

“A person that touches anything tamei, or either the carcass of a tamei wild-animal or the carcass of a tamei domestic-animal or the carcass of a tamei swarming-creature, and though (the fact) is hidden from him, he has become-tamei, and so has incurred-guilt;” Wayiqra/Lev. 5:2. (Schocken)

“But anyone that does not have fins and scales, (whether) in the seas or in the streams, from all swarming-things in the water, from all living beings that are in the water- they are detestable things for you! And they shall remain detestable things for you: from their flesh you are not to eat, their (very) carcasses you are to detest. Any one that does not have fins and scales in the water- it is a detestable thing for you!”, Wayiqra/Lev. 11:10-12. (Schocken)

“This is the Instruction for animals, fowl and all living beings that stir in the water, all beings that swarm upon the earth, that there may be a separation between the tamei and the pure, between the living creatures that may be eaten and the living creatures that you are not to eat.” Wayiqra/Lev. 11:46-47. (Schocken)

Cuttlefish, Janthina, and Murex Trunculus are in the category of unclean and detestable. Those believing that the Written Torah is the only Torah inspired by the Elohim of Israel, are not able to accept these as a source of tekhelet. Those that hold that the Oral Torah is allowed to clarify the Written Torah, are able to accept these marine animals for use. Having said this, apparently both Rabbi Bachyei and Nachmanides taught that only what may be eaten, a clean source, may be used for the Mishkan or Temple services, (11).

The plant sources of Woad, Indigo and Spirulina are acceptable according to the laws of clean and unclean given in the Written Torah. Any objection to the chemicals chosen and used to bring forth the dye from Woad or Indigo must be applied to the Murex Trunculus, as the exact chemicals may be interchanged for all three, (12). These dyes are all indigo and chemically identical. Urine aged to form ammonia could have been used in the ancient process, but soda ash, Madder root, lime or lye are alternatives that can also be used and were easily available to the ancient Israelites. Fermentation was also used for all three dyes. Initially, Ptil Tekhelet used a recipe for Murex Trunculus involving Woad to make the fermentation vat.  Since Woad contributed it's own indigo pigment to the vat, it was dropped and cockles' meat, from mussels, were added to ferment the vat, (13).

Evidence of Woad has been found in ancient Egyptian fabrics, an ancient tassel in Qumran and as far back as the Neolithic times. Dr. Curtis Ward cites 8 sources with different examples of ancient woad use in the Mediterranean area, (18). What is the most telling is that it is mentioned in the Mishna that a Rabbinic decree regarding a kohen whose hands have been stained with Isatis Tinctoria or Woad was made: 'A priest whose hands are deformed, may not raise his (hand) palms (to bless the people). R Yehudah says: even those whose hands are stained with Woad may not raise their (hand) palms, because the people stare at him', Mishnah, Megillah, 4:7. So here, all along, was evidence that the Kohanim worked with Woad. The only way for hands to be stained with Woad is to have them submerged into the bright yellow solution and upon removing, the oxygen in the air turns the yellow to a bright blue, bonding permanently onto the hands.

Indigo is mentioned in the Talmud as 'Kela Ilan' and is referred to as a fraudulent dye because it is difficult to distinguish from the more expensive tekhelet, referring to dye from a sea animal or Chilazon, (19). Woad appears to have been lumped in with Indigo as Kela Ilan at times, but it may be distinguished in the references because Woad is colour fast, sky blue and grows in the Mediterranean. Also Indigo did not appear in the Mediterranean region till the Greek and Roman era, so it did not make it into early archaeological findings in that area.

I could not find any mention of Spirulina in the Talmud or in historical references.

Cuttlefish, Janthina and Murex Trunculus fall under the heading of Chilazon in the Talmud. It is recorded that the chilazon's body resembles the ocean, it has bones and cartilage, it carries a shell and it has legs in it's head, (20). There is no mention of a specific name to the creature in the Talmud and thus the mystery for the followers of the Oral Torah. Interestingly Ptil Tekhelet, using a snail, omit some of this description, notably that it has bones and cartilage and it has legs in it's head!, (21). They do say that piles of Murex shells discarded after the extraction of this dye were found in Tyre, and dated from Biblical times. This would be the home of the ancient Phoenicians who were famous for their use of this dye in it's purple form, but not necessarily evidence of use by Ancient Israel,(8, 21).  The Rabbanite concept that the blue dye is extracted from the gland of a sea snail dates no earlier than the year 200 C.E.,(22) and if ever used by them, for a time following that, would not prove that it was the original tekhelet used for the Mishkan and by the Ancient Israelites.  Again, because it has been proven that the Murex snail dye could not have been a blue until the invention of clear glass, effectively removes it from being any candidate, of any archeological find of earlier than 100CE. see here