What makes a shofar kosher? The Gemara discusses this issue at length in Tractate Rosh Hashana. The main requirements are as follows:
- the shofar must be made from a kosher animal
- the shofar must be a minimum length
- it should not have any holes, cracks or plugs
- it should be uncoated
When a horn is formed into a proper shofar, it can be rendered pasul (unfit, nonkosher) at various stages of the production process. According to Rabbi Moshe Flumenbaum of HaSofer, most of the shofars produced in Israel are made by workers who are paid by the piece, not by the hour. The worker may inadvertantly make a hole in the shofar or cause it to crack. To avoid incurring a loss, an unscrupulous worker may then take some horn dust, mix it with glue that becomes invisible when dried and patch the horn. He can then twist it into a shape that further hides the defect, and then sand and polish the horn to the point where it looks and sounds like a kosher shofar. The only ways to ensure the shofar was not patched is through on-site supervision or an X-ray!
Adding silver or leather decoration to a shofar renders it nonkosher because even a slight change in the sound the shofar produces renders it unfit. The same applies if a lacquer coating is applied.
Likewise a shofar may not be painted (Shulchan Aruch, Orach Chayim, 586, 17). The only permitted decoration is carving into the keratin itself — as long as this does not significantly alter the shofar’s sound.
Shofar: Kosher Supervision
Sometimes a shofar will have kashrut certification, but the supervision merely ensures that the shofar was made from a ram’s horn or checks for cracks, patches and lacquer coating — only after the shofar is completed, when these problems are very hard to detect.
Keep in mind that the larger shofars are more difficult to make and frequently have problems during production, which is why the larger shofars are considerably more expensive than smaller ones.