First, I need to know how much 20 volume crème develpor I need to add to these tubes of color. 1.The brand is Ion #5rc-5.4 light copper brown and the other is #9n-9.0 very light blonde and are these two compatible...

[QUOTE=full of color37;1528646]first, I need to know how much 20 volume crème develpor I need to add to these tubes of color. 1.The brand is Ion #5rc-5.4 light copper brown and the other is #9n-9.0 very light blonde and are these two compatible for one being the base color and the other for highlighting

Can you be a little more specific?
Do you want to mix the colour together? If so, don't!
If you mean you want the correct ratio for mixing the developer with the ion dye, then it's usually 1:1. But I could be wrong as it's different with different dyes. Read the manufacturers instructions.