20 volume
no
yes
you can't mix developer with developer to make another developer
No.
Equal parts of 10V. Developer + 20V. Developer= 15 Volume Developer
Mix equal parts of 50V.+10V. to yield 40 V. developer
You have to have a actuall hair color to mix with it. Use 2oz of the color and 4oz of the developer and mix. And apply to your hair
Mix equal parts of developer and Wella color.
Equal parts of 5 volume developer + 15 volume will yield approximately 10 volume.
If mixed equally, you will get 30 Volume.
If you mix them in equal parts, you now have 25 volume developer.
Equal parts of 30V + 40V= 35V.