פירוש על עבודה זרה 5:12

כלי תשמיש – of a meal, and specifically metal utensils or earthenware utensils that are coated with lead, and glass utensils are like metal utensils [as well].

If [a Jew] purchases cooking-utensils from a non-Jew, those which are customarily used with cold liquids, he must immerse;
Those which are customarily used with hot liquids, he must be dip in boiling water;
Those which are customarily made white-hot in the fire, he must make white-hot in the fire.
A spit and grill must be made white-hot, But a knife may be polished and is then ritually clean.
This mishnah discusses how a Jew can make usable cooking utensils that were purchased from a non-Jew. Since the non-Jew surely used these utensils to cook unkosher products, the utensils must be “kashered”.
The general principle in this mishnah is quite simple: the way that a utensil was normally used is the way that it is made usable by the Jew. The Talmud explains that this is learned from a midrashic reading of Numbers 31: “any article that can withstand fire these you shall pass through fire and they shall be clean, except that they must be cleansed with water of lustration; and anything that cannot withstand fire you must pass through water.”
A utensil that was used generally with cold foods may be washed off and it is kosher. Since it was used with cold, it did not absorb the unkosher food and therefore it need only be cleaned with water. If a utensil had been used with hot boiling liquids, such as a soup pot, it absorbed more than the utensil used with cold. Therefore it must be dipped in boiling water to remove the unkosher elements that it has absorbed. Utensils that had been used directly on the fire, such as the spit and the grill, become even more absorbent. The only way to kasher them is to make them white hot.
A knife is a special case: it must be polished so that the outside layer of the knife is actually removed. This is because the knife, which is pressed with force into foods, tends to become more absorbent, even though it is not used directly on the fire. Remember that the knives in those days were not made of the hard stainless steel of which our knives are made.
Congratulations! We have finished Avodah Zarah.
Again this is the point where we thank God for helping us to finish learning the tractate and commit ourselves to going back and relearning it, so that we may not forget it and so that its lessons will stay with us for all of our lives.
I hope that you found this tractate as interesting as I did. We live in a world where the relationship of Jews to non-Jews is, thank God, much better, especially in North America, and therefore many of the rules in the tractate probably strike us as harsh and not applicable to our lives. However, Jews still face the problem of assimilation that Rabbis faced 2000 years ago and we still have much to learn from them on this topic. This tractate is that we saw the way that the Rabbis dealt with living in a society where they were a minority.
Tomorrow we begin to learn Tractate Avoth, also known as Pirkei Avoth or Ethics of the Fathers.

את שדרכו להטביל – meaning to say, a utensil that is appropriate to become pure through ritual immersion and it doesn’t require another improvement/repair for example that it is used through cold water.

מטביל – in a Kosher Mikveh for the ritual immersion of a woman and its immersion permits it.

להגעיל – as for example, kettles and pots of metal whose use is through boiling water.

יגעיל – in hot water that we bring them into a kettle filled with boiling water and we leave them in there a bit and this is after we scour them and remove their rust/mold and afterwards immerse them in a Mikveh that is kosher for the immersion of a woman, and they are permitted.

ללבן – utensils that we use them through the fire with something dry, without broth/juice of meat as we explain further on such as the examples of spits/skewers and grilles.

מלבנו באור – until there would be sparks flying off from them, and afterwards, we immerse them and they are then permitted.

שפה – insert it in the ground hard ten times, and if there are no indentations in it, one can eat cold on it, or we sharpen it with its whetting implement of stone and one can eat on it, even boiling [foods]. But if there were indentations in it, we make it white-hot, and all of them that were used before they were not boiled or before they were made white-hot or before it was immersed [in a Mikveh], it is permitted.