Se’eth, the second and less intense nega than the bahereth, can be an immediate indicator of tumah.
The whiteness intensity of the se’eth is a matter of tannaic dispute, Rabbi Meir says that it is the color of an egg membrane and it’s (lesser in whiteness) companion has the whiteness intensity of white wool but the sages say the reverse; the se’eth has the whiteness intensity of white whool whereas it’s companion (aka sapachath) has the whiteness intensity of an egg’s membrane.
Moist or dry?
This needs some explanation, as the egg’s membrane is quite faint when moist but turns ultra-bright once dry, this makes the moist version the likely shade discussed by chazal since the egg membrane is the faintest of all four shades of white listed.
Perhaps this may validate Rabbi Meir – as he is known to probe to the inner meaning of names הווה מדייק בשמא- where seeth means high and the dry egg membrane is indeed stark white(we malbim tazria min. Ch. 56)
As with all נגעים on the skin, the minimal shiur for טומאה of a שאת is כגריס.
However, the שאת color alone doesn’t render the person immediately tammei unless it turns the hair inside it white. What the se’eth itself can do is require a quarantine period of 7 days.
The rambam defines the color tone of שאת as beginning from white wool up until the whiteness of an egg’s membrane1)1, while in no case is the שאת brighter than the בהרת but actually inferior in terms of whiteness and brightness2)2. Talmud Yerushalmi explains that the נגע השאת is “higher” than it’s surrounding skin just as a shadow’s appearance is “higher” than the appearance of sunlight.3)3
What it indicates
The kli yakar writes that the שאת, as it’s translated meaning of “high”, is afflicted to the person who has גסות הרוח, who makes himself “higher” than acceptable in g-d eyes.
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