Why has the enamel crawled in from the edges?

Why has the enamel crawled in from the edges

Why has the enamel crawled in from the edges? This is because the piece is almost certainly over fired (example right); to combat this problem you must reduce the temperature and/or the firing time. If you are using a torch for firing, the flame has enveloped the piece. Try holding the torch further away so that the flame hits the back of the blank and forms a 45° angle.

SwedishPolandDutchItalyIndiaHungaryGermanFrenchCzechBrazilSpainRussiaJapanChinaEnglish