Makeup used to create the appearance of an even skin tone, which is affected by the optical geometry of the makeup and/or particles comprised in the makeup. When light is aimed in the direction of an object, the light may be directed as a reflection completely in one direction determined by the angle of incidence (e.g., similar to the well-known reflection phenomenon seen with a mirror). Light may also scatter in many different directions in a manner referred to as diffuse transmittance. Furthermore, the light may transmit through the makeup, if the makeup possesses sufficient transparency. This phenomenon also involves the refraction of light. As the light passes through the object its speed (or velocity) and wavelength changes according to the index of refraction, defined by the ratio of the speed of light in vacuum to the speed of light in the object. The light bends as it passes through the object.
When the surface of the skin is smooth, light is absorbed, reflected and scattered off the skin and is observed as a color according to how much light is absorbed and scattered. Blemishes on the skin absorb, reflect, and scatter light to varying degrees, and thus, prevent the appearance of a flawless complexion. Furthermore, when light is directed toward a wrinkle, it is unable to be reflected or even scattered and the eye observes a darkness where the line or wrinkle is located on the skin.
Additionally, the angle at which make up worn by a person will affect visual impression received by the observer, such looking straight at the person (zero viewing angle) will appear different to the observer than other portions of the made up anatomy seen at a different angle.
Light manipulation, therefore, has become an important development in makeup used to create the appearance of an even skin tone.
Current makeup systems generally comprise traditionally high refractive pigments (e.g., titanium dioxide (TiO2) and iron oxide colorants) which manipulate the light, and modify the appearance of the surface to which it is applied. However, this method has been found to be undesirable because it is too opaque and reflective, i.e., due to the isotropic back scattering properties of TiO2, a high concentration of TiO2 provides high coverage at the expense of a natural look. In contrast, a low concentration of TiO2 achieves a cosmetic film that looks more natural (e.g., not chalky) at the expense of sufficient coverage. Therefore, it has been suggested that pigment not only diffuse light but also have a certain amount of reflectance to overcome the mask-like appearance of titanium dioxide. While it is always desirable to have an optimal combination of naturalness and coverage, it is not readily achievable because of the isotropic nature of the traditional pigments.
Generally, diffusion or blurring may be achieved with spherical soft focus particles such as nylon and polyurethane particles and/or interference pigments. However, although anisotropic pigments have been designed, there is an ongoing need for makeup compositions to provide sufficient coverage, e.g., to create the appearance of an even skin tone, and achieve a natural look upon application.