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laboratory testing

color protection and uptake

All of the dyed hair tresses are labeled to allow for identification. Baseline L, a, b measurements were taken using a Hunter Lab Ultra Scan XE colorimeter to characterize the initial color of hair.

“L” refers to the lightness on a scale of 0 to 100, “a” denotes the red-green color range (positive value denotes higher red) and “b” represents the yellow-blue color range (positive value denotes higher yellow). This is demonstrated in the schematic below.

Hunter Labs Colorimeter

Changes in the color of the tress are evaluated by calculating the difference in these parameters relative to a reference state (i.e. ΔL*, Δa*, and Δb*).

In addition, it is common to report an overall color change, ΔE.
ΔE = √[ΔL*2 + Δa*2 + Δb*2 ]

Delta E is the color difference between the treated hair and original hair color. For the Initial Color Value and some other parameter, such as, ∆L*, ∆a*, ∆b*, ∆C*, ∆H*,


Using ULTRASCAN, one measures L, a and, b (Figure A1).
L scale measures the lightness or grayness component of the colored sample, with L=0 for black and L=100 for white. ∆L values (difference between after and before treatment) indicate either a lighter (positive values) or a darker (negative values) sample resulting from any treatment protocol.

a scale measures the chromaticity differences in the red-green components of the color observed. Positive changes in a are correlated with increases in the red component.

b scale pertains to chromaticity differences in the yellow-blue components, positive changes in it being an indication of increased yellowness.

Using these L, a, b values, it is possible to calculate other parameters. Changes in C (denoted by ∆C) represent changes in chroma. ∆E is a measure of the total color difference between the sample (after) and sample (before). ∆H indicates changes in hue.

C = (a2 + b2)0.5                                                   
 ∆C = (Cafter – Cbefore)                                                         
∆L = Lafter - Lbefore              
∆E = [(∆L)2 + (∆a)2 + ∆b)2]0.5                       
∆H = [(∆E)2 – (∆L)2 – (∆C)2]0.5    

∆L is a good monitor of fading, since it is a brightness parameter. It is seen that ∆E, the parameter representing color changes, is a very good monitor of the fading phenomenon, since changes in it are, in fact, a “composite” of changes in brightness and color. It incorporates more than one type of change in the fading phenomenon. Hence, changes in it are a good indicator of color fastness under any treatment protocol studied.

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