Rif Pesachim 8b {Pesachim 30b continues; Avoda Zara 75b-76b; Pesachim 30b}

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8b

{Pesachim 30b continues}
in a kli rishon {=first vessel, the vessel in which the water was boiled, as opposed to kli sheni, into which the contents were transferred}.

Rav Huna the son of Rav Yehoshua said: And a wooden pot ladle must be boiled in boiling water in a kli rishon. He holds: As it absorbs, so it exudes.

Seize this rule in your hand - that wooden vessels, vessels of iron and other types of metal, and vessels made of dung, which always used with chametz in a kli rishon {fashion} need be boiled {hag'ala} in a kli rishon, and those which were used in a kli sheni, such as plates and the like, when you throw over them hot water and let it sit in it until it exudes, it is fine, for we learn this from the vessels of gentiles, of which are written {Bemidbar 31:23}:

כג כָּל-דָּבָר אֲשֶׁר-יָבֹא בָאֵשׁ, תַּעֲבִירוּ בָאֵשׁ וְטָהֵר--אַךְ, בְּמֵי נִדָּה יִתְחַטָּא; וְכֹל אֲשֶׁר לֹא-יָבֹא בָּאֵשׁ, תַּעֲבִירוּ בַמָּיִם.

23 every thing that may abide the fire, ye shall make to go through the fire, and it shall be clean; nevertheless it shall be purified with the water of sprinkling; and all that abideth not the fire ye shall make to go through the water.

{Avoda Zara 75b}
The Sages learnt {in a brayta}: If one acquires vessels {for food} from a gentile: Things which had not been used at all, one immerses them and they are pure. Things which had been used with cold, such as cups, jugs and flasks, one rinses them and immerses them, and they are pure. Things which had been used for hot, such as boilers, kettles and heating vessels, one boils them and immerse them, and they are pure. Things which had been used upon a flame, such spits and grills, one must make them white-hot and immerse them, and they are pure.

{Avoda Zara 76a}
How do we boil {mag'ilin - to purify vessels}?
Rav Huna said: A small vessel must be placed inside a large vessel.

What, then, is to be done to a large vessel?
Come and hear: For there was a certain vessel in the house of Rav Ukva {our gemara: Rav Akavia} so he made for it
{Avoda Zara 76b}
a rim of dough around its mouth, filled it with water, and boiled.
Rava said: Who could have been so wise to do this except Rav Ukva, who is a great man. And he held that as it absorbed, so does it exude. Just as it {the rim} absorbs from the splashings, so too it will exude via splashings.

And these words are during the other days of the year. But on {and for} Pesach, when it is forbidden to use dough, he makes a rim of mud and boil it.

{Pesachim 30b}
They inquired of Amemar: Glazed vessels, may one use them on Pesach. Regarding green ones {which are made from an earth containing alum crystals and absorbed freely}, there is no question, for they are certainly forbidden. When is it a question? About white ones and black ones. If they have splits, there is no question, for they are certainly forbidden. When is it a question? When they are smooth. Then what?
He said to them: we see that they exude {=that they are porous}