Why will ceramic fiber board be black and smoky when it is used for the first time?

Ceramic fiber board will be added some organic additive in production process, so there will give off organic additive when usage, so it will be black and smoky. After all organic additive releases, ceramic fiber board will become white.

If do not want to have this phenomonen exist, it can be calcination at high temperature, or make it into ceramic fiber flet by vacuum suction molding without adding organic additive.