1,151. Altering a Shofar

Hilchos Shofar, Succah v’Lulav 1:6

If one adds anything to a shofar, whether of shofar material or of some other substance, it is invalid. If one coats a shofar with gold on the inside or the mouthpiece, it is invalid. If he coats it with gold on the outside and the sound is altered, it is invalid. If the sound is unaffected, it is valid. If a person puts a shofar inside another shofar, then if one hears the sound of the inner shofar, he has fulfilled his obligation but if he hears the outer shofar, he has not. If one widens the narrow end of a shofar and narrows the wide end, the shofar is invalid.

Hilchos Shofar, Succah v’Lulav 1:7

If a shofar is long and one shortens it, it remains valid. If one scrapes horn from the inside or the outside it is valid even if all that remains is the thin shell. A shofar is valid regardless of whether the sound it produces is thick, light or dry because any sound a shofar makes is valid.