Vietnamese pots are particularly hand made. They are fired for up to 3 weeks at high temperatures in wood fueled kilns. Sometimes bits of ash fly about in the kiln and sometimes pots explode. In this way, bits of clay, ash or glaze can end up on other pots. You don’t get the kind of flawless glazing that one gets from the natural gas fired kilns but the trade-off is that you get a stronger pot. Vietnamese pots are well known for their strength, thickness and wonderful blue glazes.