China Dishes, Porcelain

The Aish Rabbi Replies

Utensils used together with hot non-kosher food absorb some of the non-kosher taste and must be kashered to remove the taste. However, only certain types of material can be kashered. The Torah distinguishes between metal and earthenware. Leviticus 6, when discussing the laws of sacrifices, describes what to do with utensils a sacrifice was cooked in. (Sacrifices which are eaten may be consumed for only a short period of time; afterwards they become forbidden.) Verse 21 distinguishes between a copper utensil, which can be boiled to be kashered, and an earthenware one, which must be destroyed.

Numbers 31 discusses a similar topic. Israel defeats Midian in battle and carries off much booty. In verses 21-23 Elazar the Priest explains to them how to make the captured utensils kosher. He lists several types of metal (most of the ones known in their time), telling the people to purify them via fire or (boiling) water, depending how they were used for non-kosher.

(The simple rule is that items which were used for non-kosher directly on the fire, without the medium of water, must be kashered with fire. Most other utensils may be kashered with boiling water. See here for the details of the kashering process.)

In practice, most natural materials which do not resemble earthenware may be kashered. Apart from metals, this includes wood, bone, stone and natural rubber. (Pure granite or marble countertops may likewise be kashered with boiling water.)

However, many materials in common use today are considered questionable. These include china, porcelain and stoneware. In general the practice is not to kasher them. However, in cases involving great loss, one may wait 12 months, kasher them in boiling water 3 times, and then use them (Igrot Moshe Y.D. I 43).