## 1 Introduction  
Designing and marketing aesthetic products is of growing importance in markets where many basic needs of consumers have been satisfied. As core product attributes, such as quality and functionality, become increasingly indistinguishable with a lack of uniqueness, manufacturers are shifting their focus or efforts away from concrete product characteristics towards less tangible features such as aesthetics [1, 2].  
Nowadays, the research objectives in cosmetics are obviously to create products that are always more innovative and more successful, and above all, to perfectly come up to the sensory expectations of consumers. Consumers generally choose a cosmetic cream for its functions or its promise of efficiency but are mostly seduced by the pleasure it brings to them, especially in terms of texture. Therefore, over the last few decades, sensory analysis has been developed and used to describe and quantify texture characteristics of cosmetic products [3, 4, 5, 6, 7, 8, 9, 10, 11].  
[PERSON] et al. [6] investigated various suspensions of cosmetic powders concerning the perceived skin feel after application. Their results indicated that cosmetic powder particles should be small with a rather irregular shape to lubricate the tribological contact between fingertip and skin surface to have a more \"powdery\" skin feel or tactile perception. Despitethe existence of tactile perception [7; 8; 9; 10], to our knowledge, there exists little research on the evaluation of the appearance or visual perception of the cosmetics themselves. [PERSON] et al. [11] provides valuable data evaluating the appearance of \"glossiness\" for cosmetic products. They used the Spectrum Descriptive Analysis method to discriminate and characterize aqueous phases of cosmetic oil-in-water emulsions containing xanthan gum. Based on their research, according to xanthan gum concentration, there is consistent linear relationships in solution for the appearance of glossiness. However, while the result presented in their study is valuable when the contents are matched, another concern is that the data are not versatile enough for application to emulsions used in a variety of cosmetic products.  
Emulsions are colloidal dispersions of a liquid in another immiscible liquid stabilized using a surfactant and/or solid particles [12; 13]. In the cosmetic industry, scattering medium with fine particles suspended or dispersed such as emulsions are widely used in color cosmetics, skincare, and personal care products. [PERSON] et al. [14] revealed that the particle size distribution in dispersion changes simply by changing the stirring speed in the manufacturing process of cosmetic products. They also found that the optical properties of the dispersions changed with the change in particle size distribution. As an application of their technology, [PERSON] et al. [15] succeeded in improving the sun protection factor (SPF) of cosmetic creams by varying the stirring speed. The optical properties are values that determine the propagation of light within a semi-translucent and scattering medium. Therefore, it can be an indicator of the performance of a cosmetic product, such as SPF, and would be an indicator of the appearance of the product. If the relationship between the optical properties and appearance can be clarified, it will provide a useful indicator for controlling the appearance of various products.  
The purpose of this study is to clarify the relation between the scattering properties and the change in visual perception by using dispersions of fine particles with titanium dioxide or zinc oxide as scattering medium. As for visual perception, behavioral studies were conducted with human panelists with a custom-designed apparatus to inspect the samples and evaluate the two visual sensory quantities \"glossiness\" and \"translucency\".