It better to use 20 vol or less on relaxed hair. Anything higher might be too strong, and can cause damage to hair.
30
20 Volume developer should be used when toning hair.
20 or 30 Volume developer is recommended for blonding.
particularly, yess. it depends on what hair dye it is for the vol. of the developer. but, MOST hair dyes, require 20-30 vol. happy hair dyinng.
Which developer you use will depend on the color you want to achieve. A 20 developer will give you a darker color than a 30 or 40 developer.
30 or 40 depending how bright you want it
30
Yes, bleach or a high lift color mixed with 30 vol. developer is needed in order to lighten hair.
Well the higher the developer is the faster it shall get to being lighter. So if you use 30 you shall get lighter hair faster.
No, diluting a 30 vol hair developer with water will not change the volume strength of the developer. To make a 20 vol developer, you would need to mix the 30 vol developer with a neutralizing solution or a lower volume developer.
No. It is not recommended to use hair dye without the developer or without it's original content. However if you were to use a temporary rinse then a developer isn't needed. If you are using any dyes that are not already ready to go (previously mixed by the manufacturer) then you will need to follow those instructions and mix your developer with the color.
30 volume developer will lighten the hair three levels.