How to Use 10, 20, 30, and 40 Volume Developer to Lighten Dark Hair
If you have dark hair and want to lighten it, you will need a hair developer. However, walking down the hair care aisle and seeing bottles labeled 10, 20, 30, and 40 volume can be incredibly confusing. Lightening dark hair is a complex chemical process. Using the wrong developer can lead to severe hair damage, …

































