Luster measurements of lips treated with lipstick formulations

In this study, digital photography in combination with image analysis was used to measure the luster of several lipstick formulations containing varying amounts and types of polymers. A weighed amount of lipstick was applied to a mannequin's lips and the mannequin was illuminated by a uniform beam of a white light source. Digital images of the mannequin were captured with a high-resolution camera and the images were analyzed using image analysis software. Luster analysis was performed using Stamm (L(Stamm)) and Reich-Robbins (L(R-R)) luster parameters. Statistical analysis was performed on each luster parameter (L(Stamm) and L(R-R)), peak height, and peak width. Peak heights for lipstick formulation containing 11% and 5% VP/eicosene copolymer were statistically different from those of the control. The L(Stamm) and L(R-R) parameters for the treatment containing 11% VP/eicosene copolymer were statistically different from these of the control. Based on the results obtained in this study, we are able to determine whether a polymer is a good pigment dispersant and contributes to visually detected shine of a lipstick upon application. The methodology presented in this paper could serve as a tool for investigators to screen their ingredients for shine in lipstick formulations.