Mishnah Parah 5:5: We may sanctify with all vessels, even with vessels made from feces, stone vessels and earthen vessels. And we may sanctify in a boat. We do not sanctify with the sides of [broken] vessels, nor in the crevices of a machatz [a large jug used for drawing water, which had hollow crevices], nor with a barrel lid [which had hollow indentations for handles], nor with cupped hands; for we only fill, sanctify, and sprinkle chatat water in a vessel. [Similarly,] a tight seal only saves [from impurity the contents of] vessels [but it does not save the contents of things not considered vessels]; and only vessels can save from [the impurity of] earthenware vessels [in which they are contained]. [Earthenware vessels have the property that they can only become impure from their inside however if something impure is placed in such a vessel, anything else inside the vessel and the vessel itself become impure. However, if a vessel which cannot become impure or an earthenware vessel are tightly fitted with a cover, or 'tight seal,' the inside is considered protected from the outside and thus things inside cannot become impure. Similarly, if a sealed vessel is inside an earthenware vessel, despite the fact that a ritually impure object placed in the earthenware vessel makes everything inside it impure, the contents of a tightly sealed vessel which is incapable of becoming impure nonetheless remain pure. Our mishnah states that in order for these applications of 'tight-seal' to apply, the container must qualify as a vessel.]

בְּכָל הַכֵּלִים מְקַדְּשִׁים, אֲפִלּוּ בִכְלֵי גְלָלִים, בִּכְלֵי אֲבָנִים, וּבִכְלֵי אֲדָמָה. וּבִסְפִינָה, מְקַדְּשִׁין בָּהּ. אֵין מְקַדְּשִׁין לֹא בְדָפְנוֹת הַכֵּלִים, וְלֹא בְשׁוּלֵי הַמַּחַץ, וְלֹא בִמְגוּפַת הֶחָבִית, וְלֹא בְחָפְנָיו, מִפְּנֵי שֶׁאֵין מְמַלְּאִין וְאֵין מְקַדְּשִׁין וְאֵין מַזִּין מֵי חַטָּאת אֶלָּא בְכֶלִי. אֵין מַצִּילִין בְּצָמִיד פָּתִיל אֶלָּא כֵלִים, שֶׁאֵין מַצִּילִים מִיַּד כְּלֵי חֶרֶס אֶלָּא כֵלִים:

Mishnah Parah 5:6: The craftsman's egg [a type of plaster mold with a cavity for creating vessels] is valid [for sanctifying the chatat waters]. Rabbi Yosse invalidates it. A chicken's egg[shell], Rabbi Meir and Rabbi Yehuda validate it; and the Sages invalidate it.

בֵּיצַת הַיּוֹצְרִים, כְּשֵׁרָה. רַבִּי יוֹסֵי פוֹסֵל. בֵּיצַת הַתַּרְנְגֹלֶת, רַבִּי מֵאִיר וְרַבִּי יְהוּדָה מַכְשִׁירִין, וַחֲכָמִים פּוֹסְלִין: