Reference for Kelim 24:7

שָׁלֹשׁ פִּנְקָסִיּוֹת הֵן. הָאֱפִיפוֹרִין, טְמֵאָה מִדְרָס. וְשֶׁיֶּשׁ בָּהּ בֵּית קִבּוּל שַׁעֲוָה, טְמֵאָה טְמֵא מֵת. וַחֲלָקָה, טְהוֹרָה מִכְּלוּם:

There are three types of notebooks: an <i>afiforin</i> [a large writing tablet which can be folded and used as a chair] is susceptible to <i>midras</i> impurity; and one that has a hollowed space to hold wax [which can then be carved into] is susceptible to corpse impurity; and one which is flat [and written upon with ink or charcoal, not wax] is pure from all [types of impurities].

Jastrow

Jastrow