Commentary for Mikvaot 9:2
קִלְקֵי הַלֵּב וְהַזָּקָן, וּבֵית הַסְּתָרִים בָּאִשָּׁה, לִפְלוּף שֶׁחוּץ לָעַיִן, וְגֶלֶד שֶׁחוּץ לַמַּכָּה, וְהָרְטִיָּה שֶׁעָלֶיהָ, וּשְׂרָף הַיָּבֵשׁ, וְגִלְדֵי צוֹאָה שֶׁעַל בְּשָׂרוֹ, וּבָצֵק שֶׁתַּחַת הַצִּפֹּרֶן, וְהַמִּלְמוּלִין, וְטִיט הַיָּוֵן, וְטִיט הַיּוֹצְרִים, וְגֵץ יְוֵנִי. אֵיזֶהוּ טִיט הַיָּוֵן, זֶה טִיט הַבּוֹרוֹת, שֶׁנֶּאֱמַר (תהלים מ), וַיַּעֲלֵנִי מִבּוֹר שָׁאוֹן מִטִּיט הַיָּוֵן. טִיט הַיּוֹצְרִין, כְּמַשְׁמָעוֹ. רַבִּי יוֹסֵי מְטַהֵר בְּשֶׁל יוֹצְרִין וּמְטַמֵּא בְּשֶׁל מָרֵקָה. וְגֵץ יְוֵנִי, אֵלּוּ יִתְדוֹת הַדְּרָכִים, שֶׁאֵין טוֹבְלִין בָּהֶן וְלֹא מַטְבִּילִין אוֹתָן. וּשְׁאָר כָּל הַטִּיט, מַטְבִּילִין בּוֹ כְּשֶׁהוּא לַח. וְלֹא יִטְבֹּל בָּאָבָק שֶׁעַל רַגְלָיו. לֹא יִטְבֹּל אֶת הַקֻּמְקְמוּס בַּפֶּחָמִין, אֶלָּא אִם כֵּן שִׁפְשֵׁף:
[The following are also considered interpositions on a person attempting to immerse:] tangles [of hair] on the chest, or on the beard, or in the hidden areas of a woman, a secretion outside the eye, or a crusting on the outside of a wound, or a bandage that is upon it, or dried sap, or hardened feces on one’s flesh, or dough underneath a fingernail, or dirt particles, or Greek clay, or potters’ clay, or Greek mud. What is Greek clay? This is the clay used for pits, as the verse states, (Psalms 40) "And he raised me out from the pit of tumult, from the Greek clay." The potters’ clay is as it sounds. Rabbi Yose would consider that of potters to be pure [i.e. and not to be an interposition preventing something from being purified by immersion], and he would consider impure [i.e. and therefore an interposition] that [earth] which was used to polish and mend vessels. And regarding Greek mud, this is [white earth used to make] road pegs, in which one may not immerse, nor may one immerse them [i.e. one may not immerse while they are on his body]. And regarding all other clay, one can immerse in it when it is moist. And one should not immerse with the dust on his feet. One should not immerse a kettle with soot [on it], unless he rubbed [it off].
Bartenura on Mishnah Mikvaot
English Explanation of Mishnah Mikvaot
What is meant by 'miry clay’? This means the clay in pits, for it is written: "He lifted me out of the miry pit, the slimy clay" (Psalms 40:3).
"Potter's clay" according to its literal sense. Rabbi Yose declares potter's clay clean, but clay for putty unclean.
And "road-clay."
These become like road-side pegs in these [kinds of clay] one may not immerse oneself nor immerse [other things] with them;
But in all other clay one may immerse when it is wet.
One may not immerse oneself with dust [still] on one's feet.
One may not immerse a kettle with soot [on it] unless he scraped it.
Section one: This section is a list of things that block successful immersion.
Most of these are self-explanatory. Sweat-crumbs are formed on your hands when they are dirty and you rub them together and little balls are formed (this is actually quite a clever description of those little things).
The various types of clay are explained in the continuation of the mishnah.
Section two: Miry clay is clay found in pits the word comes from the verse in Psalms.
Sections three and four: These seem to be self-explanatory.
Section five: All of these types of clay become like "road-side pegs." This refers to a person who walks in mud and has around his legs cakes of mud. One is not allowed to immerse with these types of clay on him, nor can one immerse vessels with this type of mud on them.
Section six: Other types of mud do not block immersion, as long as they are wet.
Section seven: The dust on one's feet block immersion.
Section eight: Before one immerses a kettle, one must scrape off the soot. The words "unless he scraped it" can also refer to the dust on one's legs.