Question: how much powder bleach to 20 volume developer?
Answer: RECOMMENDED MIXING: For off-the-scalp application, mix 1 oz. of Color Charm Powder Lightener with 1 oz. of the appropriate Wella Developer (20 or 30 Vol) in a non-metallic bowl. For on-the-scalp application, use only 20 Vol Crème Developer by mixing 1oz.