Blue black hair help

[vanity*louise]

Hey,
I have a client this weekend who would like to go Blue black.
She is black on the ends from home dying, and her root regrowth is about a level 5.
I have not used the special mix tones before so was hoping for some advice on how to mix them, i dont want the roots to glow blue and the ends black! Eek.
I was looking at other threads on here and it looks like using 0/88 doesnt really show up the blue very well, is this true?
I mostly use Wella, sometimes Goldwell but am open to other brands if people know of a better option.
Thanks for any advice! Xx

 

[Grace_Hair]

I never use mix tones but I was taught the rule of 10.

Base 9 you use 1cm of mix tone.
Base 5 you use 5cm of mix tone
Base 1 you use 9cm of mix tone.

You'll need to pull out all previous colour. And I would assume pre-lighten. But I've never had anyone wanting blue-black