Colour and transparency for Ethnic makeup

It is necessary to impart colour in the correct balance for different skin tones. It is also equally important to understand that people from different backgrounds have various skin care concerns, which need to be addressed. African skin contains less moisture; pore size also varies amongst races.

Texturising agents can help to provide skin smoothness, and fill in lines and wrinkles. They can add moisturisation, brightness, a soft focus and optical effects to the skin. Nylon powders improve application onto the skin while silica or polymer beads create a soft focus effect. Multi-colour pearlescent pigments can create shimmering tonal effects to the skin.

Microspheres with a high degree of porosity absorb oil (sebum) from the skin, thereby improving the overall finish. These microspheres, classified as sebum control powders, suppress greasiness for a shine-free effect.

Pigments for diverse shades

Figure 1_-_contrast_ratios_for_cosmetic_raw_materials

Figure 1: Transparency/opacity measurements of wet films cast from pigment or powder dispersions (concentration: 10 percent solids in jojoba oil)

 

For foundations, generally inorganic pigments are used; especially iron oxides and titanium dioxide. These pigment dispersions may consist of surface-treated pigments milled together with a dispersant and a liquid silicone, water, an ester, or natural oils.

Iron oxides are suitable for formulation and can be found in all shades of foundation from the lightest to the very dark tones. Formulators balance the colours using computer software linked to a spectrophotometer as well as visually evaluating the shades to match the specific target.

Titanium dioxide is widely used as the primary white pigment to achieve colour balance and opacity. Zinc oxide can also be used.

Transparent iron oxide pigments, sometimes considered as special effect pigments, possess a high degree of transparency in liquids when the difference between the refractive indices of the pigments and the medium is very low. Transparent iron oxides are typically considered to be nanoscale pigments. As particle sizes become smaller, their chalky appearance becomes less noticeable.

Because of their transparency, these pigments would allow complex, darker skin tones to shine through the foundation makeup and give a more natural colour appearance.

Transparent red iron oxide (Fe2O3), transparent yellow iron oxide (Fe2O3·xH2O) and transparent black iron oxide (Fe3O4) may be used in combinations to achieve desired hues within the light to dark shade ranges.

Ultramarine pigments can also be used in foundation formulations. Ultramarine blue may be used either to supplement or replace black iron oxide in specific shades where a more vibrant, darker tone is essential. Because of ultramarine blue’s low refractive index it has a high degree of transparency and becomes very dark when paired with oils or esters that are close to its refractive index.

Colouring for ethnic skin tones

Many foundation products now include an SPF with sunscreen actives. Both pigmentary and nano-sized pigments of titanium dioxide and zinc oxide may be included together in these formulations.

Titanium dioxide ranges from about three to 10 percent and zinc oxide, which is used less frequently, can range from one to 10 percent. The lower end of the range, three to four percent or less, is used for Ethnic or black African shades.

There are other inorganic colours, which are also incorporated in all foundations. These include:

Higher concentrations of iron oxides are required for Ethnic shades. In some cases the base formulation may need to be adjusted so that the iron oxides are better dispersed within the overall system promoting better colour value.

Greater levels or different types of emulsifiers or dispersants may also be required to address this. Predispersed pigments in oils and solvents available from ingredients’ suppliers work well in solving this problem.

Additionally, increased levels of iron oxides in emulsion makeups can affect stability and rheology. This is due to differences in the oil absorption of the pigments and the presence of water soluble salts. By surface treating iron oxides with coatings such as silicones, isopropyl titanium triisostearate, fatty acids, lecithin or other substances, it can help to improve colour dispersion and stability.

Transparency and Opacity

Figure 2_-_foundation_make-up_shades

Figure 2: Colour mapping of an extended shade range that includes tones for Hispanic, Asian, African-American and Caucasian skin

 

Opacity, transparency and translucency need to be carefully engineered as foundation products can be too chalky on Ethnic skin.

Experts from Kobo Products (Kobo) measured the contrast ratio of over 30 raw materials. Contrast ratio is a measure of transparency/opacity of an ingredient or a formulation. This property is measured with a spectrophotometer by obtaining the ratio of black Y/white Y (see Figure 2).

The company made five measurements for each material tested and then took the average. As illustrated in the graph for contrast ratios, Kobo produced a series of pigments and powders dispersed in jojoba oil.

It was observed that microspheres are essentially transparent when dispersed in the right medium. A number of fillers, such as barium sulphate and lithium magnesium silicate are also very transparent. Talc and mica (muscovite), the most commonly used fillers, have good transparency and are also relatively inexpensive. Biotite is a filler that combines the properties of mica with iron oxides.

The remaining microspheres and fillers are translucent, with the exception of boron nitride, is opaque. Boron nitride can be used for improving all shades by replacing titanium dioxide or zinc oxide at varying levels. It has excellent cosmetics properties because of its hexagonal plate structure similar to the well-known lubricant, graphite.

The inorganic pigments vary in opacity depending upon particle size and chemistry. Ultramarine blue and other ultramarines are translucent as is nano-sized zinc oxide. Nano-sized titanium dioxide is of low opacity.

Colour/Shade Mapping

In Figure 2 Kobo provides an example of how an extended shade range may look when mapped out in LCH colour space. Its team measured a number of products currently in the marketplace.

Quadrant I represents the very lightest shades of makeup, primarily for Caucasian skin. Quadrant II represents more medium light and natural shades, and Quadrant III demonstrates slightly darker shades with more chroma and an increasingly yellow hue, appealing more to Hispanic and Asian skin tones. Quadrant IV represents the darkest tones that are more suitable for African skin. These are generally higher in chroma and may be either yellow or red in hue.

Understanding skin from a multicultural perspective will enable brands and manufacturers to achieve their technical targets and to satisfy a broader category of consumers throughout Africa.

Ingredients such as silica, ethylene/methacrylate copolymer, nylon, polymethyl methacrylate and elastomers can deliver benefits to the skin to preserve the finish and create a soft glow through light diffusion.

Cosmetic scientists can engineer better products for Ethnic skin by designing matrixes with various particles, refractive indices, and the surrounding mediums of innovation.

By Edward Bartholomey and Stacey House


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