The black residue or speck you may see on the Blackstone griddle is likely harmless in small amounts and just carbon deposits. Oils and fats can, when overheated, will lead to carbon deposits in your food. Cooking oils with low smoke points cause carbonization at a high temperature and residue rubbed off with the food from the griddle. Although unpleasant, it didn’t seem toxic in such small amounts. Another reason for Blackstone's black residue is seasoning. The seasoning is not meant to last forever and can start to flake after the first few meals you cook. The oil or wax coating on the griddle will start to disintegrate with high heat and will not hold up for long.