It seems appropriate that this contribution on natural colors is being written as the author is surrounded by autumn foliage in the Hudson River Valley. The brilliant golds, reds and shades of orange that replace summer’s diverse bright greens draws an impressive caravan of city dwellers every weekend to view Nature’s display and pick apples. The chromophores that generate these appealing colors in nature can also function as natural colorants in cosmetics. Ethnographers have concluded that prehistoric people decorated their bodies with pigments long before they began wearing clothing. “Body painting only requires the availability of pigments and imagination,” wrote Jablonski, who also referenced the archaeological discovery of pigments dating to 75,000 years ago.1
Cosmetic chemists often use color to tint solutions and emulsions, or to add pigment to cosmetics for skin application. To do so, they must be aware of the commercially available materials and know which are allowed under local regulations. From a natural certification perspective, the guidelines promulgated by certifying bodies also should be considered.
Dye vs. Pigment
Before exploring the role of natural colorants in cosmetics, it is important to review the difference between a dye and a pigment. Dyes are soluble molecules that produce color by transmitting observable wavelengths and absorbing those that are unseen. For example, chlorophyll molecules absorb primarily in the blue and red regions of the visible spectrum, and transmit in the green region.2 In contrast, pigments essentially are opaque insoluble particles that produce effects by reflecting the perceived color and absorbing the remainder of the visible spectrum. Most powdered particles appear as variations of white since they scatter all visible wavelengths; so whether they are titanium dioxide, powdered sugar or fine salt crystals, these materials appear as variants of white to the human eye.
Alternatively, a material that absorbs all visible wavelengths and reflects none appears black. This phenomenon is less common. Interestingly, formulators of color cosmetics consider carbon black as being much blacker than iron oxide black due to the differences in light absorption. As any chemist who has scooped carbon black from a partially full bag can attest, it is difficult to accurately see where the powder level begins because virtually no light is reflected.