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4. Treating leather on Shabbos:
Introduction: It is Biblically forbidden to tan leather on Shabbos, as stated in Admur 321/2. Softening the leather and oiling leather in order to soften it is part of the Biblical tanning prohibition, and one who does so is liable. If one oils the leather without intent to soften it but with intent to polish it, it is Rabbinically forbidden due to a decree that one may come to oil it in order to soften it and tan it. If one does not have intent either to soften or to polish the leather then it is permitted to do so if he does not oil the leather directly but rather first oils himself and then places the leather on him.
A. Oiling leather:
One may not smear his feet with oil when it is inside a new shoe or sandal because the leather softens through the oil residue and resembles [the prohibition of] tanning [leather]. [This applies even if one has no intention to soften it, or even to polish it, nevertheless it is forbidden due to it appearing like softening. If however one intends to soften it or polish it then it is a complete Biblical or Rabbinical prohibition, as explained next.]
Smearing feet with oil: However, one may smear his feet [with oil] and then afterwards place his feet into his shoes [if one has no intention to soften it, or even to polish it]. As well one may smear his entire body [with oil] and roll on top of leather without any worry [of a prohibition] as long as the oil which drips from his body is not enough of the amount needed to tan the leather. [Although] even if it contains enough oil to polish it the leather it is permitted [to be done] as long as that he does not intend [on rolling on the leather] in order to polish it, [as if he does intend then it is forbidden] due to a decree against [coming to] tan.
It is forbidden to oil new leather on Shabbos unless one fulfills the following three conditions:
1. One first oils his body and then brings it into contact with the leather
2. One is not doing so with intent to soften the leather
3. One is not doing so with intent to polish the leather.
Does the tanning prohibition apply to an already tanned leather item?
What is the definition of new shoes?
Some Poskim rule that so long as the shoe has been worn one time it is now considered old.
May one oil old shoes on Shabbos with intent to polish it or soften it?
Some Poskim rule that old leather may have any of the above actions performed to it, such as oiling for polishing purposes or softening purposes. However, from Admur ibid it is possible to learn that the softening prohibition applies in all cases, and the leniency awarded to old leather is only that one may oil his skin while wearing it, and not that one may intend to do so to soften it or polish it. Practically, one is to be stringent in this matter and not oil any shoe on Shabbos in order to polish it, and certainly in order to soften it, even if the shoe is defined as old.
May one polish shoes on Shabbos?
It is forbidden to polish shoes on Shabbos using shoe polish. Furthermore, it is forbidden to polish it even using oil or other non-colored material. This applies to both new and old shoes, as stated above.
Shining the show with a brush or cloth-no liquid: Some Poskim rule it is forbidden to shine the shoe even without using any liquid, but through rubbing on it a cloth or brush, or even through rubbing one’s hands over it.
Cleaning a shoe without intent to shine: It is permitted to clean a shoe on Shabbos if one does not have any intent to shine it. It is permitted to use even a cloth to lightly remove the dust. Some Poskim however write that the custom is to only allow doing so using one’s hands or through banging the shoe on the floor, and not through using a cloth.
What is the law if a gentile polished one’s shoes on Shabbos?
It is forbidden to wear the shoes until after Shabbos Kdei Sheyaasu. However this applies only if the shoe was not wearable without the polish. If however the shoe was wearable without the polish then it may be used.
B. Softening and hardening leather on Shabbos:
One who tramples on leather until it becomes hard or one who softens it with his hands and stretches and flattens it the way it is done by professionals is liable for the tanning prohibition. [Practically one is to be stringent even by old leather.]
May one fold and stretch his leather shoes on Shabbos in order to soften them?
No, doing so contains the tanning prohibition.
May one soften a new baseball glove on Shabbos?
May one enter shoetrees into his shoes on Shabbos to upkeep the shoes?
One may do so if his intent is to simply prevent the leather from shrinking, such as by wet shoes, [and only if within the process of inserting the shoe tree he does not stretch out the shoe]. However one may not do so if his intent is to stretch the leather of the shoe, or to undo its folds, as this action contains the tanning prohibition.
 327:4; Michaber 327:4; Shabbos 141b
 Implication of Admur 327:5; M”B 327:12
 Admur ibid; M”B 327:16; Shabbos ibid and Rashi ibid
 Admur ibid; Michaber ibid; Shabbos ibid
 Admur ibid; Rama ibid; Rambam 23:10; See Q&A regarding what actions are permitted to be done to new leather!
The reason: New leather carries the tanning prohibition while old leather does not contain the tanning prohibition. [M”B 327:13] As new leather is commonly softened and hence carries the tanning prohibition while old leather is not commonly tanned. [Olas Tamid 327:6; Tehila Ledavid 327:3]
Other opinions: Some Poskim rule it is forbidden to oil even old shoes. [Raavad, in opinion of Kalkeles Shabbos and M”B 327:12] Practically, it is forbidden to oil even old leather shoes as there are people that are ignorant of Halacha and will come to do so even to new leather. [M”B ibid in name of Chayeh Adam]
 Admur ibid; Rama ibid
 See M”B 327:15
 M”B 327:16
 From here we learn that oiling the leather in order to tan it is a Biblical prohibiotion, while oiling the elather in order to polish it is a Rabbinical prohibition.
 Tehila Ledavid 327:3 based on Rambam
 Tehila Ledavid 327:3 based on Bahag 20 Shabbos
 Tehila Ledavid 327:3; Implication of M”B 327:12 and 13 in the lenient opinion
 So is implied from 327:5 in which Admur does not limit the prohibition to new leather.
 Conclusion of Chayeh Adam and M”B 327:12
The reason: As a) Perhaps the Rama and Admur ibid did not intend to allow oiling old leather in order to soften it or polish it. B) There are Poskim who rule the prohibition applies equally to old leather. [brought in M”B ibid] C) There are people that are ignorant of Halacha and will come to do so even to new leather. [M”B ibid in name of Chayeh Adam]
 M”B 327:12
The reason: This is forbidden due to the dyeing prohibition [M”B 327:12] as well as due to the tanning prohibition. [M”B 327:16] being it is forbidden to polish the shoe due to that one may come to tan it.
 This is forbidden due to due to the tanning prohibition [M”B 327:16] and possibly even due to the dyeing prohibition, if by doing so it brings out the color of the shoe. [M”B 327:12; See Sheveut Halevi 7:43]
 Zichro Toras Moshe [of Chayeh Adam] 39:2; Bris Olam Miabeid 3; Piskeiy Teshuvos 327:5
 Aruch Hashulchan 327:4; Shut Rav Chaim Zonenfeld 38; Shevet Halevi 5:37; Ateres Moshe 1:108; Bris Olam Miabed 3; Piskeiy Teshuvos 327:5 and 302:3 footnote 43 in name of Poskim
 Shevet Halevi ibid; Ateres Moshe ibid; Bris Olam ibid; Piskeiy Teshuvos ibid
 M”B 327:16 in name of Tiferes Yisrael
 Teshuras Shaiy 2:152; Meorer Yesheinim 112; Piskeiy Teshuvos 327:5
 327:5; M”A 327:2; M”B 327:12; Rambam 11:6
 See previous Q&A and footnotes there! However see Piskeiy Teshuvos 327:4 that onl;y prohibits doing so to new leather.
 Piskeiy Teshuvos 327:4
 SSH”K 15:48; Piskeiy Teshuvah 308:15
 Piskeiy Teshuvah ibid
 Michzeh Eliyahu 42 [Rav Pesach Eliyahu Faulk Sheyichyeh, Rav in Gateshead]; Toras Shabbos 302:13; SSH”K ibid
 So rules Minchas Yitzchak 9:58; SSH”K; Piskeiy Teshuvos, based on Admur 308:42 which rules: “A shoe, whether new or old, which is fastened onto a shoe-tree is permitted to be removed from it, whether by removing the shoe tree from the shoe or whether by removing the shoe from the shoe-tree, as there is no prohibition involved in moving the shoe-tree, as the shoe-tree has the status of a vessel, and it is just that it is designated for a prohibited use [being that it removes the folds and stretches the leather-Minchas Yitzchak ibid], [of which the law is] that it is permitted to move it in order to use its space, which in this case refers to the inner space of the shoe in which the shoe-tree is inside of.”