* How much darker you're going: If you're only going one or two shades darker, you can often get away with a lower volume. If you're going significantly darker, you might need a higher volume.
* Your hair's porosity: Porous hair absorbs color quickly, so a lower volume might be sufficient. Less porous hair might need a higher volume to open the cuticle and allow the color to penetrate.
* The specific hair color product: Always refer to the manufacturer's instructions for the hair color you're using. They will recommend a specific developer volume for darkening hair.
General Guidelines:
* 10 Volume: This is the gentlest option and deposits color only. It's best for subtle darkening, covering gray (when used with a demi-permanent or deposit-only color), and refreshing existing color.
* 20 Volume: This is a good choice for going one or two shades darker, covering gray hair, or when you want a little lift (opening the cuticle) along with depositing color. It is the most common volume developer.
Important Considerations:
* If you're unsure, start with a lower volume. You can always reapply with a higher volume if needed, but you can't undo damage caused by using too high of a volume.
* Never use more than 20 volume to darken hair. Higher volumes are designed for lifting (lightening) hair and can cause unnecessary damage when darkening.
* Strand test: Always do a strand test before applying the color to your entire head. This will help you determine the processing time and whether the chosen developer volume is appropriate for your hair.
* Consult a professional: If you're unsure about which developer volume to use, it's always best to consult a professional hairstylist. They can assess your hair's condition and recommend the best approach for achieving your desired color.