Kelim, Chapter Twenty-Eight, Mishnah Six
1) If a patch was sewn on to a basket, it conveys one grade of uncleanness and one of unfitness.
2) If it was separated from the basket, it conveys one grade of uncleanness and one of unfitness, but the patch becomes clean.
3) If it was sewn on to cloth it conveys two grades of uncleanness and one of unfitness.
4) If it was separated from the cloth, it conveys one grade of uncleanness and one of unfitness, while the patch conveys two grades of uncleanness and one of unfitness.
5) The same law applies to a patch was sewn on to sacking or leather, the words of Rabbi Meir.
a) Rabbi Shimon says that it is clean.
b) Rabbi Yose says: if [it was sewn] on leather it becomes clean; but if on sacking it remains unclean, since the latter is a woven material.
Section one: The piece of cloth (the patch) discussed in today’s mishnah was already defiled with midras impurity. Then someone used it to patch up a basket, thereby transforming it from a vessel that is sat upon to a vessel that is not sat upon. The patch loses its midras impurity. The entire basket, including the patch, is now impure by virtue of its contact with something that had midras impurity. This is first degree impurity and anything that touches it will now have second degree impurity. This is what the mishnah means when it states “it conveys one grade of uncleanness.” And when terumah touches something with second degree impurity, it becomes “unfit,” although it is not impure. This is the meaning of “one of unfitness.”
Section two: If he separates the patch from the basket, the basket retains its level of impurity, but the patch is pure. Note that it has shed its midras impurity (see 18:8).
Section three: If he puts the patch on a piece of cloth, it doesn’t lose its midras impurity and all of the cloth becomes impure with midras. This is because the function of the cloth has not changed. Something that has midras impurity is a “father of uncleanness” and conveys first degree uncleanness to things that come into contact with it. Therefore, this cloth conveys two degrees of uncleanness (father to first degree to second degree) and one degree of unfitness (second to third degree).
Section four: When it is removed from the cloth, the cloth’s level of impurity is reduced. Now it only has “contact with midras” impurity, which is first degree.
The patch, however, never changed its status, and therefore it still has midras impurity.
Section five: According to Rabbi Meir, it doesn’t matter whether the cloth onto which the patch was sewn was made of cloth, sacking or leather. Rabbi Meir holds that sacking and leather are really types of cloth and therefore in all cases when the patch is removed, it retains its impurity.
Rabbi Shimon holds that sacking and cloth are not types of cloth. Therefore, it is like patching a basket which is of a different type, and when he removes the patch it will be pure.
Rabbi Yose holds that sacking is a sub-category of cloth because like cloth it is woven. However, leather is different from cloth and therefore, if used to patch a cloth and then removed, the patch is pure.