Sentence:  At this point overfiring begins, as is shown particularly by the volume curve, which indicates decided bloating, so that at 1450°C the clay has about the same volume it had at 1050°C before vitrification took place. At 1450°C it is, therefore, decidedly <WSD>overfired</WSD>. However, its excellent burning behavior is apparent from the long temperature range. 
Meaning of the word marked with <WSD> tags:  Fired at a high (or excessively high) temperature.