Physics tells us that, when a container is sealed, if you apply heat, pressure will build within the container. Conversely, if you apply pressure, whatever is contained within that container will grow hot.
Potters are artists. More appreciated possibly in less developed parts of the world where their wares provide for the transportation, storage and preparation of food. Pot making is not a simple task, it requires great skill not only in molding the clay but also in its baking – if the fire is too hot, the pot will crack, making it useless for cooking.
The unscrupulous pot maker learned to place wax in these cracks and cover this over with potting material in order to make the pot appear whole. The unsuspecting buyer would take this home and, when it was employed over the fire containing the liquids required in preparing their food, the wax would melt, the food would be ruined.
Neither that the pot maker nor his pots were “sincere”, a word derived from sin ceres which in Latin means “without wax”.
When under pressure, it’s going to get hot.