Mikvaos 9:1-2

Mikvaos 9:1

The following interpositions block a person’s immersion: wool threads, flax threads and the ribbons on girls’ heads. Rabbi Yehuda says that wool and hair are not interpositions because water passes through them.

Mikvaos 9:2

More interpositions include matted hair on one’s chest or beard, or on a woman’s genitalia; secretions outside the eye; a scab outside a wound and the bandage covering it; dried juice; lumps of excrement on one’s body; dough under one’s nails; particles of dirt, muddy clay, potter's clay, and road clay. “Muddy clay” means the clay in pits as per Psalms 40:3, “He lifted me out of the muddy pit, the slimy clay.” “Potter's clay” is intended in its usual sense. Rabbi Yosi rules potter’s clay clean (i.e., not an interposition) but clay used for putty unclean. “Road clay” is identical to roadside pegs. One may not immerse oneself nor objects in them but one may immerse in other types of clay when they’re wet. One may not immerse himself with the dust on his feet; one may not immerse a kettle with soot on it unless he rubbed it.