Ferro Sulphide comes in two types: Iron (III) (Fe2(SO4)3), and Iron (II) (FeSO4). Ferrous Sulphate compounds are the by-products of the steel finishing process. Prior to coating and plating, steel sheets are passed through pickling baths of sulphuric acid, and then Ferro Sulphide is produced. This by-product can then be used in other manufacturing processes, such as in the reduction of chromate during cement production. Ferro Sulphide can also be used to stain concrete, limestone, and sandstone a rust color.