With extreme care. Never smoke a bowl after washing it, the water seeps into the poreholes of the clay and will EXPLODE when heated. The safest way is to wash a bowl after it has cooled down, and then let it air-dry for many hours as to make sure the water has evaporated out of the clay matrix. The key element is thermal shock. Repeated temperature fluctuations will cause the glaze to crack as one part of the glaze is cooling/heating up at a different rate than its surrounding, which will propagate cracks.