Reference for Shabbat 148:5
אמר רבא האי מאן דעבד חביתא חייב משום שבע חטאות תנורא חייב משום שמונה חטאות אמר אביי האי מאן דעבד חלתא חייב אחת עשרה חטאות ואי חייטיה לפומיה חייב שלש עשרה חטאות:
Rabbah son of R. Huna said: He who boils pitch is liable on account of cooking. But that is obvious? — You might argue, Since it hardens again, I might say [that he is] not [liable]. Hence he informs us [otherwise]. Raba said: He who makes an [earthenware] barrel is culpable on account of seven sin-offerings.<span class="x" onmousemove="('comment',' So MS.M., deleting 'on account of' in cur. edd. (i) The clods of earth are first crushed and powdered — this constitutes grinding; (ii) the thicker balls which do not powder well are removed — selecting (iii) it is then sifted; (iv) the powder is mixed with water — kneading; (v) the resultant clay is smoothed when the cast of the vessel is made — smoothing; (vi) the fire is lit in the kiln; and (vii) the vessel is hardened in the kiln — boiling. ');"><sup>9</sup></span>