20 volume peroxide is correct. 30 volume is used to make hair much lighter so if you get just a band then it's probably just a freak occurrence - for an unknown reason that portion has either reacted more vigorously or the peroxide solution hasn't been mixed/agitated correctly before use.
Answers & Comments
20 volume peroxide is correct. 30 volume is used to make hair much lighter so if you get just a band then it's probably just a freak occurrence - for an unknown reason that portion has either reacted more vigorously or the peroxide solution hasn't been mixed/agitated correctly before use.