Question: what is the difference between a 10 and 20 developer?
Answer: The 10 volume developer is a standard oxidizing level for permanent, no-lift hair color. It's designed for use when you want to add a color tone or tint to the hair of the same lightness level. ... The 20 volume developer opens the hair cuticle but unlike 10 volume, it provides lifting of the hair by one to two levels.