Q.  The instructions in the bleach I use indicate I should not mix bleach in a metallic container, I am assuming this means all types of metal bowls.  If that is the case why is it acceptable to place the bleach and hair between two pieces of foil (metal)? Andre, San Pedro, CA.

A. The cautionary note against mixing bleach in metallic bowls dates back to the time when bowls were made mostly of copper or iron. Copper and iron were quite common and inexpensive materials prior to the commercial introduction of plastics and the availability of affordable stainless steel.

Copper and iron bowls can oxidize or rust very easily and can result in very active metallic ions (strong catalysts) that may leach into any liquid medium contained in these bowls. Because of these strong catalysts, bleach mixtures prepared in these metallic bowls frequently break down and lose their lifting power.

Stainless steel on the other hand, does not have this problem because it does not oxidize easily and does not leach active ions into the bleach. Similarly, aluminum also is stable and resists oxidation and leaching of active ions. That is why the aluminum foils that come in contact with the bleach on the hair are harmless and do not affect the bleaching action.

Therefore, to guard specifically against the possible use of rusty iron or copper metallic bowls with hair bleaches, manufacturers include the cautionary note in their bleaches against all metallic bowls. This would be a much safer approach than saying, for example, “Mix only in oxidation-resistant metallic bowls”.