Kelim, Chapter Seventeen, Mishnah Seventeen
1) The base of the goldsmiths anvil is susceptible to uncleanness, but that of the blacksmiths is clean.
2) A whetting-board which has a receptacle for oil is susceptible to uncleanness, but one that has none is clean.
3) A writing-tablet that has a receptacle for wax is susceptible to uncleanness, but one that has none is clean.
4) A straw mat or a tube of straw:
a) Rabbi Akiva rules it is susceptible to uncleanness;
b) But Rabbi Yohanan ben Nuri rules that is it clean.
c) Rabbi Shimon says: the hollow stalk of colocynth is subject to the same law.
5) A mat of reeds or rushes is clean.
6) A reed-tube that was cut for holding anything remains clean until all the pith has been removed.
Section one: The base of the goldsmiths’ anvil is susceptible because it has a place to store small pieces of gold that break off. However, the blacksmiths’ anvil has no such receptacle and therefore it is clean.
Section two: A whetting board is used for sharpening a knife. If it has a receptacle to store oil it is susceptible but if it is not it is clean.
Section three: To write on a writing tablet one would rub wax on the tablet and carve into the wax. If the tablet has a receptacle to store the wax it is susceptible.
Section four: According to Rabbi Akiva a straw mat or straw tube both last long enough to be considered a vessel and therefore they are both susceptible to impurity. Rabbi Yohanan ben Nuri says that they do not last long enough, and therefore they are clean.
Rabbi Shimon says the same debate between Rabbi Akiva and Rabbi Yohanan ben Nuri also exists with regard to the hollow stalk of a colocynth plant or a mat made from colocynth. The following is the intro to colocynth that I found on Wikipedia: The colocynth, also known as bitter apple, bitter cucumber, egusi, or vine of Sodom, is a viny plant native to the Mediterranean Basin and Asia, especially Turkey (especially in regions such as İzmir), Nubia, and Trieste.
Section five: A mat made of reeds or rushes is not soft enough to sit on and is therefore not susceptible to impurity. These mats are generally used for shade.
Section six: If a reed tube was cut to be used as a receptacle, it is not susceptible to impurity until the pith, the stuff inside the stalk, has been removed.