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What is it? Libun Chamor is defined as torching the vessel until sparks fly from it, or alternatively, until a sheet of its metal peels off. [Practically, today the above does not occur to the metal, as it is much denser than in previous times. Accordingly, the following other signs should be used today: 1) If the metal becomes red it is considered to have reached Libun Chamor. 2) In degrees, if one heats the item until 400 degrees Celsius, it is considered to have reached Libun Chamor.]
When is it required: All Kasherable material vessels that had Chametz baked in them without liquids are disputed if they require Libun Chamur or Hagala and practically we rule that they need Libun Chamur.
If Libun Chamor was not performed: In all cases that Libun Chamor is required for Kashering for Pesach, and one only did Libun Kal or Hagala, then one may be lenient in a time of great loss or Simchas Yom Tov in a case that one already used the pot for cooking. However, by other Issurim one may never be lenient.
Libun Chamor on Chol Hamoed Pesach: One may Kasher a vessel through Libun even on Pesach.
Ben Yomo: Libun Chamur may be performed onto a Ben Yomo vessel, even initially.
Self cleaning oven:
An oven with self cleaning mode reaches a temperature of 900° F and is thus equivalent to Libun Chamur. This helps to perform Libun Chamor to itself, as well as to all Kasherable utensils that are placed in it while on a self-cleaning cycle. An oven with a “Continuous cleaning” cycle does not reach this level of heat and is not equivalent to Libun Chamur.
Libun Kal is defined as torching the vessel on the inside until its opposite side becomes Yad Soledes. When burning Chametz from a rusty area or crack, the custom is to do so until the point that a piece of straw would burn if it were to be placed on other side. [Placing a pot on a flame until the pot reaches Yad Soledes is not defined as Libun Kal, as the flame must be placed inside the pot, and pas sthrough every part of the inside.]
When is it required: Libun Kal is as an alternative Kashering method to Hagala. In certain cases, Hagala does not help, and thus Libun Kal must be used. For example, if a vessel contains cracks or rusty areas that cannot be cleaned, then those areas must have Libun Kal performed to them to burn any Chametz that they may contain. Likewise, if a vessel is so long that part of its middle area will not enter the pot, then one may do Libun Kal to that area. It is not valid to perform Libun Kal to a vessel which requires Libun Chamor, as explained in A.
Ben Yomo: Libun Kal may be performed even onto a Ben Yomo vessel, even initially.
 Admur 451:13
 See Ohel Yaakov Hagalas Keilim p. 24-25 for a discussion on this matter
 Admur 451:13; Michaber Y.D. 121:4
Regarding Basar Bechalav: A [non-earthenware] pot which absorbed meat and then milk or vice versa never needs Libun Chamor. [Admur 451:13 in gloss; Shach 121:7] However, an earthenware oven requires Libun Chamur. [Admur 494:16; 461:1] An earthenware pot cannot be Kashered. [Admur 451:9]
 Background: If the vessel absorbed the Chametz directly, without any liquid involved, such as by a baking pan, then a dispute exists as to what type of Kashering it needs. Some say that even Hagala [placing it in boiling water] suffices. Their reasoning is because Chametz before Peach is permitted, and therefore does not require such extreme heat to be Kashered. However, other Poskim rule that it requires “Libun Gamur” which means that it must be heated until sparks begin to fly off from it, or until a layer of it peels off. Practically, we rule like the latter opinion, even bedieved [such as that one already used the pot to cook in] that it needs libun gamur. [Admur ibid]
 Admur ibid; See Rama 451:4; M”B 451:32
 Admur 452:19
 See Admur 452:19
 Admur 4651:10 “Fill the inside with coals”; Igros Kodesh Rebbe Rashab 5:226; See Tosafus Avoda Zara 33b; Smag Lo Sasei 148; Sefer Hateruma 161; Hagahos Maimanis Machalos Assuros 11:15; Or Zarua Avoda Zara 2:169; Hagahos Ashri 2:22
 Admur 451:10 and 37; See Igros Kodesh Rebbe Rashab 5:226; Vetzaruch Iyun from 451:44 that implies the other side must have straw burn on it
 Admur 451:16 and 19 and 38
 See Admur ibid; Piskeiy Teshuvos 451:18
 See Admur 451:10 and 37; Taz 451:8; Rama 451:4; Igros Kodesh Rashab 5:226; Ohel Yaakov Hagalas Keilim p. 27 who writes that Libun Kal is better than Hagalah; Nitei Gavriel 65:13
 Admur 451:16 and 19 and 38
 Admur 451:37
 Admur 451:13; Rama 451:4; M”B 451:32
 See Admur 452:19