More About Klaf

Blank Klaf

In ancient times there were 3 types of skin1 used as a writing surface: “Gevil”, which is un-split leather; “klaf”, which is the upper layer of split hide; and “duchsustus”, which is the lower layer of split hide.2 In Talmudic times, mezuzos were written on duchsustus, tefilin were written on klaf and Sifrei Torah were written on gevil. The practice of splitting the klaf fell out of use around the time of the early Rishonim. The current practice is to scrape off and discard the lower layer of the skin (the duchsustus) and just use the upper layer (the klaf). There are still a few Sofrim (mostly Yemenite) who write Sifrei Torah on gevil, but most modern Sofrim use klaf for everything.

When writing on gevil the letters are written on the outer surface (the side that had hair). When writing on klaf the letters are written on the inner surface (the side that was against the flesh). Writing on the hair-side of klaf, or the flesh-side of gevil, invalidates the STAM. The other halachos pertaining to STAM are the same for klaf and gevil, and when the Gemara discusses these halachos, the words “gevil” and “klaf” are used interchangeably.

Since klaf needs to be processed lishma, ideally each piece of klaf should be processed specifically for the desired STAM item: Klaf that will be used for a Sefer Torah should be processed “lishem kedushas Sefer Torah”; klaf for tefilin should be processed “leshem kedushas tefilin”; etc. If the final destination of a given piece of klaf is not known, the klaf can be processed conditionally-lishma: When putting the hides into the tanning solution, the klaf-maker says, “I am processing these skins for the sanctity of a Sefer Torah, on the condition that I can use it for any other purpose I desire”. Most of the klaf on the market is processed conditionally-lishma. Klaf processed without provision is considered more mehudar and is sometimes available at additional cost.

It is preferable for klaf to be made by  by a Jew. If it is not possible for the Jew to do the actual work, the next best thing is for him to at least assist a non-Jew in the various tasks while they both say they are tanning the hides lishma. If even that is not possible, a non-Jew can tan the hides himself, provided there is a Jew standing next to him and telling him to process these hides lishma.3

Almost all of the klaf in common use today is processed in lime, following the opinion of Rabeinu Tam. This klaf is invalid according to the Rambam, who holds that klaf must be processed in “afatzim” — a gall-nut solution. There are a few klaf-makers who offer kalf tanned with afatzim for customers who want klaf that is kosher according to all opinions.

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  1. For a brief introduction to klaf, see STAM bits: Klaf. For information on what to look for (and what to avoid) when choosing a klaf factory see Purchasing STAM Part 4. To learn why not to judge klaf based solely on color, see White Klaf

  2. Which side of the split hide is klaf and which side is duchsustus is actually the subject of a disagreement among the Rishonim, but the majority opinion — and the consensus among the Achronim — is that the klaf is the upper layer.

  3. If the Jew was standing at a distance when he told the non-Jew to do the work lishma, or if the Jew was right next to him but didn’t explicitly tell him to do the work lishma at the very moment he puts the skins into tanning solution, the klaf is invalid. All of this follows the opinion of the Rosh. According to the opinion of the Rambam, the work must be done by a Jew.