Hair Coloring 120 colored dye molecules—which are either diffused into the hair (semi- permanent dyes) or absorbed onto the hair surface (temporary dyes). These dyes fade more quickly than the permanent dyes either 6-8 washes in the case of the former or 1-2 washes in the case of the latter. The decision on which product to use depends on a number of factors. 1. The degree of transformation the consumer desires 2. The length of time they expect the color to last. 3. The natural color of the consumer’s hair. The majority of today’s hair color market ( 80% of sales) is in the sale of the permanent hair colorants (also called Level 3 permanents). These products will be reviewed in the greatest detail within this chapter. Measuring Color There are two scales commonly used to describe color. The first is a visual assessment used by stylists to describe hair color (both the starting color of hair and final color) in terms of lightness and tone. The second is a measurement used by scientists to accurately describe the color based on a three-coordinate system.2 The stylist system used is a visual assessment of hair color vs. a set of standards. The first assessment is the lightness of the hair from Level 1 (black) to Level 12 (ultra light blonde). The second is the tone of the hair using either a letter or a number to describe the tone. Table 2 shows the shade descriptors. As an example, a medium brown with gold tone would be described as a 3G or a 3/3 shade, and a light ash blonde would be 8A or 8/1. The most frequent method of accurately measuring color is using a spectrophotometer to give a three-number coordinate that describes all colors visible to the human eye. The CIE L*a*b* color space is the most commonly used color space. The L* value measures the lightness from L* = 0 (black) to L* = 100 (white). The color is measured by a* from –a* (green) to +a* (red) and b* from –b*(blue) to +b*(yellow). For example, a medium blonde has an L*a*b* value of