Organics are literally burned out during first fire of ceramic bodies. Ball clays often contain significant organic material (the lignite imparts their dark grey to even black coloration). Excessive organics and insufficient time or oxidation will lead to black-coring of the body during firing. During this range it is the low temperature organics that are removed, others remain.
A common fault in reduction gas fired ceramic ware made from iron bearing clays. The interior cross section of the clay turns black.
|Temperatures||Carbon / iron oxidation (370-950C-)|