What volume developer should you use with majirel number 9?

When using Majirel color number 9, you should use a 20-volume developer (6% peroxide) for standard coverage and lightening. This developer is ideal for achieving a subtle lift while maintaining the vibrancy of the color. For more intense lightening or if covering gray hair, you might consider using a 30-volume developer (9% peroxide), but it's essential to monitor the processing time to avoid damage.