Yes a 40 developer will lift your hair color 4 times. It will lighten your hair.
You will need to mix it with a color and follow the directions on the box or packaging.
It will remove the pigment from your hair and lift your hair color 3 times (lighten it).
Cream developer alone will not lighten your black hair. You will need to use a bleach or lightener with the cream developer to lighten it.
20 vol
yes.
you use 20 volume developer on gray hair
When used alone, developer will do nothing to the hair. It is made to be mixed with a hair color.
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
Yes, bleach or a high lift color mixed with 30 vol. developer is needed in order to lighten hair.
Yes, but it wouldn't work as good you would have to use a lot more creme
Yes, a 50V developer can be used to lighten hair but more than likely it will break the hair and cause irreversible damage. A 30V is recommended instead.
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.
you can but it will make your hair extremely orange or brassy. It would be better for you to use bleach with the 20 volume developer..20 volume does the least amount of damage to your hair..just be sure to build the strength of your hair back up with conditioning treatments.