Avodah Zarah 75 - Purifying Winepress and Vessels
A stone winepress was usually covered with hot pitch, but to counteract the effect of fumes, wine was added to the pitch. Therefore, an idol worshipper's winepress could not be used by a Jew, but first had to be "dried." Drying meant purifying it with water and ashes. If the winepress was made of wood, which required more pitch, then Rabbi Yehudah the Prince still says that all that is necessary is that it be "dried," but the Sages require removing the pitch. If it was made of earthenware, then even if he removed the pitch, it is still prohibited, because earthenware walls absorb more wine.
If one buys food utensils from idol worshippers, then the utensils that are used only with cold food require only an immersion in the mikveh. Those that are used with hot liquids are purified in hot water. Those that are used with fire without liquid are purged in a flame. The spit and grill are purged in a flame.
Art: Felix Edouard Vallotto - Still Life with Large Earthenware Jug