TRISTIMUI. US COLOR MEASUREMENTS IN FADING STUDIES 377 GREEN (P•) ioo 8o 6o 4o 2o CONTROL .................. 178 ß _ 380 460 540 620 700 WAVELENGTH (MILLIMICRONS) Figure 8. Reflectance measurements of compacts colored with green pigment. The numerals refer to the number of Langley units of direct sunlight exposure for each com- pact. (In this case the curves for the three exposed samples are superi•nposable) The next column is the value of the minimum reflectance (R•i,•) of the unexposed control. The wavelength of the minimum reflectance was then used for the balance of the test for that compact, even though the minimum may have shifted. The last column is the Kubelka-Munk value for this particular reflectance value. Its function will be examined later. USE OF EXPERIMENTAL RESULTS These data could be used in one of several ways to answer the ques- tion of which colorant combination yields the most light-stable formula- tion. It is very important here to point out that the methods can be chosen only by hindsight, i.e., after all the data are available, the curves, the dosage forms that have been exposed to the lights, and all the num- bers that have been generated by this laborious procedure are analyzed.

378 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table II Summary of Data for First Series of Compacts Tablet Exposure (Langley Units) x y Y (MacAdam Units) /Xe /Xc /X L Rmi,• K / Smi,• White White Green P3 Green P3 Green P3 Green P3 Green 3D4 Green 3D4 Green 3D4 Green 3D4 Green 5D5 Green 5D5 Green 5D5 Green 5D5 Control 0.3120 0.3186 96.27 396 0.3120 0.3185 96.39 0 Control 0.2698 0.3254 60.39 6 0.2692 0.3255 59.78 1 178 0.2695 0.3251 59.70 1 396 0.2698 0.3250 59.81 0 Control 0.2739 0.3366 58.38 6 0.2751 0.3360 58.40 1 178 0.2814 0.3306 59.01 10 ...... 91.5 0.0039 0 0.0 0.0 92.0 0,0035 ...... 34.5 0,6218 1 0.8 0.3 34.0 0.6406 0 0.3 0.7 34.0 0.6406 8 0.3 0.5 34.5 0.6218 ...... 32.5 0.7010 4 1.4 0.0 33.0 0.6802 5 10.4 0.1 38.5 0,4912 396 0.2862 0.3305 60.75 16.0 15.5 0.5 42.0 0.3890 Control 0.2474 0.3166 44.14 ......... 23.5 1.245 6 0.2487 0.3162 44.17 1.4 1.2 0.2 24.0 1.203 50 0.2560 0.3131 46.08 8.4 8.1 0.3 28.0 0.9257 142 0.2662 0.3082 49.44 21.1 19.8 1.3 34.5 0.6036 Table III Changes in Color for First and Second Series of Compacts Tablet •Xe /L K/S*/L /x A /L •- P3 0.002 0.000 0.0 Yellow 0.011 0.039 9.6 Red 0.024 0.049 1.3 3D4 0.040 0.112 27.0 5D5 0.148 0.362 117.0 * Calculated from 100 X [(K/S)o -- (K/S)L]/[L(K/S)o]. t X Table IV Summary of Data for Second Series of Compacts Exposure (Langley Tablet units) x y Y (MacAdam Units) /Xe /Xc A L Rmi n K / Smi n Red Red Red Red Yellow Yellow Yellow Yellow Control 0.3392 0.2862 33.63 ......... 27.0 0,9868 28 0.3400 0.2864 33.69 0,8 0.7 0.1 27.0 0.0968 122 0.3384 0.2888 34.67 3,5 2.8 0.7 28,0 0.9257 452 0.3358 0.2928 37.17 11.0 8.5 2.5 31.0 0.7679 Control 0.3896 0.4050 83.10 ......... 30.7 0.7798 28 0.3904 0.4062 83.20 0.8 0.7 0.1 30.5 0.7918 122 0.3876 0.4026 83.13 1.6 1.6 0.0 32.0 0.7225 452 0.3837 0.3980 83.11 4.8 4.7 0.1 34.0 0.6406