While these seem harmless they are unbelievably damaging to hair. Many non professional hair color lines use these salts in their formulation without having to tell the consumer about these ingredients and what harm they cause. They are incompatible with other chemical services so once the product is used on the hair it is not fit to have another hair color, color remover, decolorizer, or perm put on it in order to prevent breakage or discoloration. The appeal to these products is that they have the ability to provide a vibrant dimensional color that you can do at home without the expense of a salon. This is accomplished by what they call progressive color, it leaves a permanent build-up on the strand and darkens with every application. These products also tend to dry out the hair and make it look and feel dry. The only way to remove these salts is by cutting the hair off where the metallic dye is present on the hair.
I had heard that L'Oreal Feria contained these sort of salts and while I was doing research to find out if this was true I found some very disturbing things. YES L'Oreal Feria does contain metallic salts. (source: Household Products Database) It contains at least 4 types of metallic salts: sodium metabisulfate (used in Iron rust and stain remover and stump killer, also used in the Garnier Nutrisse line) sodium dietrylaminopropyl cocoaspartamide (only in L'Oreal color) TSPP (used in toothpastes and garage and driveway cleaner) and sodium stannate (used in L'Oreal and Garnier Nutrisse). So moral of the story DO NOT USE L'Oreal Feria or Garnier Nutrisse!!! Why would anyone want to use a product that has an ingredient used to clean Iron of rust?!? This just doesn't seem like a good idea.