In professional language this process is also called stripping. You may apply this sort of lightening correction if your hair ends have got darker or you have ended up with unwanted shades.
I always apply this „colour cocktail” on wet, unwashed hair to lighten already dyed hair because it removes unwanted artificial hair pigments slowly and gently.
15g bleaching powder
30 ml of relevant oxidizer. min. 1,9% but max 9% vol (using 12 % is forbidden)
60 ml warm water
5 ml shampoo
Apply on already dyed area with precise, even moves. Apply plenty of the material!
I have written about the background pigment sin the hair, it is also true for what happens after having applied the cocktail.
The pigment remaining in the hair shows beautifully, that to what extent you have managed to lighten your hair, and you can dye your hair considering the depth of the colour you have ended up with after the „cocktail treatment”.
e.g.: if your hair has become red – copper colour, than you have managed to lighten it to colour no. 5. When dyeing your hair now, you can neutralize red – copper shade with 5/ NA