나카가와상점 Rice & Noodle Bowls

What kind of process is the 'medome' (sealing) mentioned in the descriptions of earthenware vessels or rice cookers?

When acquiring ceramic tableware or cooking utensils, you often come across instructions to go through medome before using them for the first time. As it is an unfamiliar term, it makes you want to check exactly what the process is and why it is necessary.