Keilim 22:8

If the lid of a chest is removed, the chest remains susceptible to ritual impurity because of its bottom part (the receptacle). If the bottom part is removed, the chest remains susceptible to impurity because of its lid (which serves as a vessel separately). If both the lid and the bottom part are removed, Rabbi Yehuda says that the chest remains susceptible to impurity because of its sides but the Sages say that it is rendered insusceptible. A stone mason’s seat is susceptible to midras impurity.

Keilim 22:9

If a block of wood was painted red or yellow, or if one sanded its surface, Rabbi Akiva says it is susceptible to impurity but the Sages say that it remains insusceptible until one carves a seat into it. A floor basket or a wall basket filled with straw or rags is insusceptible to midras impurity even if one modified it for use as a seat. However, if one wove over the basket’s opening with reeds or string, then it is rendered susceptible to midras impurity.