Monday, February 28, 2011

Techeles rediscovered?


NYTimes

The scholar, Zvi C. Koren, a professor specializing in the analytical chemistry of ancient colorants, says he has identified the first known physical sample of tekhelet in a tiny, 2,000-year-old patch of dyed fabric recovered from Masada, King Herod’s Judean Desert fortress, later the site of a mass suicide by Jewish zealots after a long standoff against the Romans. [...]

9 comments :

  1. Here's the problem, and it underlies some of the Amutat P'til Tekhelet's arguments as well. It is accepted without any machloqes (that I know of) that aragaman is Tyrian Purple, which we know from Roman records was made from the murex. They produce (and I wear) a blue tekheiles candidate made by the same breed of snail. The difference is that sunlight breaks down the purple to produce a blue. (Other things found in the snail's dye-producing gland act as catalysts, but don't end up in the finished product.)

    So, when someone finds murex-dyed wool, or heaps of murex shells in dye vats on the coasts of Zevulun's land (such as 3,200 or so yr old vats found in Tel Dor and Tel Shiqmona), how can one say this is evidence that the murex was used for tekheiles? Maybe you found argaman?

    -micha

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  2. True techeilles is color fast as described in Gemarah Menachos. The test described (loc cit) was used to determine whether the color was true techeilles or a cheap vegetable dye (indigo). Since apparently one could not tell them apart by appearance, one might assume that techeilles and indigo are the same color. Now, we in America are evey familiar with the color of indigo. It is the dye used in blue jeans.

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  3. Ra, the notion of "color" is more complicated than that.

    It takes three numbers to describe a color. For computers, we usually break down a color into so much red, that much blue, and a quantity of green mixed together. (Thus stimulating each kind of color-sensitive nerve in the eye the right amount for a given color.)

    For dyes, the dimensions usually used are:

    hue: where on the spectrum it is

    saturation: how much color it has

    value: how much light it has.

    This toy may help you get a better understanding by playing with the values.

    A dye has a particular hue, but if you use more or less dye per square inch, you'll change the other values. Effectively, Dr Koren is saying that while the Amutah is using the same snail as his sample, they are doing two things wrong:

    1- They're leaving it in the sun too long -- not all the purpleness should be broken down.
    and
    2- They are using much less dye per string than the sample contains.

    You are arguing with #1, as the resulting dye once fully broken down by light is exactly indigo. But because of #2, there is still no way to know if tekheiles was historically darker or lighter than denim blue. We also don't have any indication a specific amount of dye is halachically specified. Perhaps any sky-blue produced from that dye is tekheiles, whether midnight sky or the blue of a clear sunny day.

    -micha

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  4. Micha,

    how do you know what Argaman is?


    and also, how do you know that Tchelet has to have a specific frequency or shade of blue? There is no standardisation, is there?

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  5. AFAIK, there never was a question that argaman was Tyrian purple. Josephus said so, Pliny said so, the Arukh said so, R' Herzog said so... It's unlike chilazon, where doubt arose -- more like asking how I know that "chitah" means wheat.

    -micha

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  6. ari greenspan of ptil tekheletMarch 1, 2011 at 6:18 AM

    I was at dr. korens lecture. It was disappointing in my estimation. while his science is good his conclusions are mistaken

    what he claimed to have discovered has no bearing on tekhelet.
    1. it is not tzitzit
    2 it was found on masada which for most of its usage was roman and not jewish so this cloth in no way is jewish.
    3 it is a small fragment embroidered onto a cloth in his words "found near the shul"

    it IS a snail dyed fragment but that is it.

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  7. I appologize if I gave the impression that I thought that Techeiles was the same color as new blue jeans (dark blue). My point was that we could compare the color fastness of murex dye with that of indigo. It is well known that dark blue denim fades to a comfortable lighter blue color after a few washings. Will the same number of washings fade murex dye in similar fashion?

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  8. I invite R' Ari Greenspan to correct any of the following:

    The murex's gland produces precursors for a chemical called diboroindigo, regular indigo, as well as purpurase, a chemical which must be present for those precursors to combine. (Ie it's an enzyme, not one of the pieces of the final chemical.) The amount of UV light it gets (eg by being exposed to sunlight) while still in solution will impact how much of the diboroindigo keeps the boron, vs how much turns into indigo.

    So, much of the dye is actual indigo, the same chemical as from the indigo plant. The rest is very chemically similar.

    Both forms of indigo are themselves colorfast. What changes when you wash jeans is how much dye stays on the cotton. It's not like the sun will change anything in the dye itself.

    R' Dr Tendler did an experiment and found that the Amutah's dye is so colorfast, if you leave a string of techeiles in bleach the wool dissolves and one is left with blue grains on the bottom. I haven't tried the experiment.

    But no dye can stand up to a chemical that actively works on how fabric holds onto dyes -- a "reducing agent". It will fair better with normal detergent than denim will, but I think that has more to do with cotton vs wool than the presence of dibromoindigo along with the indigo.

    -micha

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  9. micha
    you chemistry is not quite right but the point is correct. regarding fastness of blue jeans, your facts are wrong.
    They are just as fast HOWEVER the fading is because the jeans are dipped dyed and just the outer few microns of the entire garment is blue. take some sand paper to them and you will quickly see white. They are abraded with time and washing and turn lighter. that is why the "pre faded" ones are called stone washed. They selectively abrade parts to create the whiteness.

    The tekhelet is dyed at the fibre level and hence can never be abraded off. And yes I also let a strand in wool and the color did not come off. We also sent a sample for a standardized permanence test of the textile industry and we came in very high on the scale.

    ari

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