Rif Rosh HaShana 6b {Rosh haShana 26b continues; 27a - 27b}

HIDE/SHOW IMAGE
6b

{Rosh haShana 26b continues}
I would have said {that the halacha is like him} even by Yovel. Therefore it informs us {that it is not}.

{Rosh haShana 27a}
Mishna:
A shofar that has split and joined back together is invalid.
If he joined parts of shofars together, it is invalid.

{Rosh haShana 27b}
If it got a hole and he closed it up, if it {the hole} prevented the sound {of tekiah} it is invalid, and if not it is valid.

Gemara:
The Sages learnt {in a brayta}: If it was long and he shortened it, it is valid. If he scraped it and left only a very thin shell, it is valid. If he covered it with gold in the place he puts his moth, it is invalid. Not in the place he puts his mouth, it is valid. If he covered it with gold inside, it is invalid. Outside -- if it changes the sound from what it was before, it is invalid, and if not, it is valid. If he placed one shofar inside another and blows it, if the sound of the inner one is heard, he fulfilled, and if the sound of the outer one is heard, he did not fulfill.

The Sages learnt {in a brayta}: If he scraped it, whether inside or outside, it is valid. If he reversed it and blew it, he did not fulfill.
Rav Papa said: Do not say that he turned it inside out like a cloak, but rather he made the wide part short and the short part wide {Rashi: via heat}, he did not fulfill.
What is the reason?
Like Rav Matna, for Rav Matna said: {Vayikra 25:9}:

ט וְהַעֲבַרְתָּ שׁוֹפַר תְּרוּעָה, בַּחֹדֶשׁ הַשְּׁבִעִי, בֶּעָשׂוֹר, לַחֹדֶשׁ; בְּיוֹם, הַכִּפֻּרִים, תַּעֲבִירוּ שׁוֹפָר, בְּכָל-אַרְצְכֶם.

9 Then shalt thou make proclamation with the blast of the horn on the tenth day of the seventh month; in the day of atonement shall ye make proclamation with the horn throughout all your land.

the way that it was borne {by the living animal = its natural shape}.

"If he joined together pieces of shofar it is invalid":
[The Sages learnt {in a brayta}:] If he added anything to it, whether of its own kind or not of its own kind, it is invalid. If it got a hole and he closed it up, whether of its own kind or not of its own kind, it is invalid. Rabbi Natan says: With its own kind it is valid; with something not of its own kind, it is invalid.

With its own kind, it is valid -- Rabbi Yochanan said: And this is where its majority is left.
This implies that when it is not of its own kind, even if its majority is left, it is invalid.