Comentario sobre Makhshirin 4:8

ופשט אב הטומאה את ידיו לתוכה טמאה – for an earthenware vessel receives ritual defilement from a primary source of ritual impurity (i.e., a corpse) that touches him, his ritual immersion did not count, for even though he was in the ritual bath/Mikveh, because the waters that are in it (i.e., the dish) interpose between him and waters of the ritual bath/Mikveh.

If a pot full of water was placed in a mikveh, and a person who was unclean by a father of impurity put his hand into the pot, it becomes unclean. The pot in this mishnah is made of earthenware, which does not become pure by having been put in a mikveh. If a person who is a "father of impurity," meaning he has a high level of impurity (for instance, contact with a dead body or with a sheretz), puts his hand into the pot, he defiles the pot.

מגע טומאות טהורה – If it was not a primary source of ritual impurity that touched it, but rather a first-degree of ritual impurity, and he is called unclean [only by reason of] contact with unclean things, that is to say, he comes in contact with primary sources of ritual defilement, then the dish is ritually pure, for an earthenware vessel does not receive ritual defilement other than from a primary source of ritual defilement, and it is found that the dish was not defiled other than on account of impure liquids that were within it that had been defiled, and they go back and defile it, and because of this it does not defile, for the waters that were within it were dipped in the waters of a Mikveh/ritual bath and purified. But the rest of the liquids, as for example, wine, [olive] oil and milk, the ritual bath/Mikveh does not purify them, for they do not consider it the dipping of a vessel, filled with an unclean liquid, so as to make its surface level with the surface of the water into which it is dipped/contact between liquids (i.e., a ceremony of Levitical purification), therefore they return and defile the dish, for the Rabbis decreed upon liquids that they would defile, as a decree because of the liquid of a person afflicted with gonorrhea and/or a woman with a flux.

But if [he was unclean] by a "touch of defilement," the pot remains clean. However, if the person putting his hand in the pot has a lower degree of impurity, meaning he touched someone who is a "father of impurity," then the pot remains clean for such a person does not defile vessels. Only a "father of impurity" defiles vessels. The water remains clean as well, for the water is in the mikveh.

But any of the other liquids [contained in the pot] becomes unclean, for water cannot purify the other liquids. However, any other liquid that might be in the pot (oil, for instance) does become impure and then it will defile the pot. The water of the mikveh purifies only water, not other liquids (see Mikvaot 10:6). See also Kelim 8:4, where the irony of this situation was discussed.