In older sources there is no explicit statement on the fastness of the Tekhelet dye. It is however implied in the prescriptions for the tests whereby indigo might be distinguished from Tekhelet that the latter dye was faster than indigo (kala-ilan) which as we know has the reputation of being very fast to light and to soap.1 ”This applies to kala ilan which is not removable by means of soap.2 Professor Rosenstiehl, professor of dyeing at the Conservatoire National des Arts et Métiers has, however, informed me that indigo, though fast to soap, is impaired by strong rubbing (frottage).3 Does it follow that Tekhelet was not superior to indigo in that respect, for otherwise the somewhat elaborate tests might have been dispensed with? The inference would seem to have the support of no less an authority than R. Gershom ben Judah “The Light of the Exile (960-1028). “Rabbi Jehudah would hand it over to the washer, Reb. Hanina’s practice was to protect the tzitzit by a sort of wrapper in delivering the garment to the laundry. Rabina would insert the tzitzit in a kind of pocket specially designed for the purpose which he would sew up before handing over the garment to the washer.4 R. Gershom in his commentary annotates as follows: “R. Jehudah would hand over the garment with Tekhelet to the washer asking him to take care that the colour of the Tekhelet does not get spoiled … he (sc. R. Hanina) would wrap the Tekhelet wound with other threads in order to protect its colour against deterioration, etc.5 According, however, to Rashi’s interpretation there is no reference here to the effect of washing upon the Tekhelet colour.6 The explanation of the passage given by the Gaon Rab Amram, an earlier author than R. Gershom, though not agreeing with that of Rashi, also involves no allusion to the impairability of Tekhelet:7

Maimonides’ Code contains an important statement which is, however, too general to be of much avail in the present inquiry . . .”As for the Tekhelet prescribed for tzitzit, it’s dyeing must be of a certain kind which produces a colour abiding in its beauty and which does not become altered, etc.8 This is somewhat vague, giving no indication of the extent of the durability and fastness of the Tekhelet dye, but it undoubtedly implies fastness to light.

The inalterability of the purple dye in general has already been discussed.

In the experiments made by William Cole with the dye of Purpura lapillus the first washing somewhat allayed the colour, though it afterwards continued insusceptible to alteration by washing. This fact, however, scarcely has any bearing upon the passage Menahot 41 b. as interpreted by R. Gershom. The language of the Talmudic statements cannot reasonably be made to apply only to the first washing.

Of far greater importance is the information supplied by Lacaze-Duthiers that the dye of Murex trunculus is not fast to washing (“ne resiste pas au lavage״). This fact must also be taken into consideration in connection with the study of the Tekhelet hillazon, or the Tekhelet-giving species of mollusc.



  1.  ״.צפון״ Compare: Baba Kama 93b.
  2.  This does not of course mean that Ka/a-ilan is not impaired by washing with soap.
  3.  My own experiments have so far not confirmed Professor Rosenstiehl’s assertion.
  4.  Menahot 41b.
  5.  R. Gershom’s commentary, ib.. in the Wilna ed. of the Talmud, 1884.
  6.  Rashi, ib.
  7.  R. Amram Gaon, Itiur tzitzit. 2.
  8.  Maimonides, Hilkhot tzitzit. I, 1.