The result is that so long as the fillets are hot they are kept from contact with the air and blackening of the metal is prevented.
Abney and Baker have shown that the pure dry chloride does not blacken when exposed in a vacuous tube to light, and that the blackening is due to absorption of oxygen accompanied by a loss of chlorine.
The oil retained traces of sulphur, which showed themselves disagreeably in the smell of soaps made from it, and in the blackening of substances with which it was used.
The metal should be fire resistant and free from scorching or blackening - cast iron is usually the best option.
Grilling or frying, and the inevitable blackening that comes with it, may actually produce unfortunate carcinogens to boot.