What does 'double-process coloring' mean?

Double-process coloring refers to the technique where two separate applications of color are used to achieve the desired results, particularly when significantly lightening the hair or making a drastic color change. This method is often employed when a light base is needed to achieve a brighter or more vivid final color.

In double-process coloring, the first step typically involves lightening the hair to remove existing pigment. This is especially important for achieving lighter shades or vibrant fashion colors. Once the hair has been sufficiently lightened, a second application of color is then applied to achieve the final tone. This two-step process ensures that the hair is lifted to the appropriate level before depositing the new color, resulting in a more vibrant and even finish.

The other approaches described do not accurately capture the essence of double-process coloring. For example, mixing two colors together usually refers to a single application process, while simultaneous application of color and developer does not specifically denote the two distinct phases involved in double-process coloring. Similarly, applying color on the roots and ends at the same time lacks the crucial step of pre-lightening that defines double-process techniques.