How much loreal developer 20 do i mix with the Loreal Preference color?

i have dark hair already, but i want a blue/black to kind of reflect off my hair. do you guys think it will show? my hair is black, shoulder length. i just recently purchaced Loreal preference ONYX SHEEN, how much of the Loreal Developer 20 do i mix in with it? how many once of each?

How much loreal developer 20 do i mix with the Loreal Preference color?

Hmmm. The directions should be on the box-even if it is a pro color. Most colors are equal parts color to peroxide. Ex 2oz of color to 2oz of peroxide, but some color lines mix a little different.

There should be info on the product somewhere. It's kinda important to mix it the way it tells you to or it may not work right. Is there a number you can call on the box?

You should be able to see the bluish tint in the light, but it may not be super noticable since your hair is already dark. Won't know til you try it. Good luck!