Pearlescent Pigments Primer Part I: The Science of the Substrates

Nacreous, or pearlescent, pigments are widely used in the cosmetic industry to add luster, sparkle, impart color or color-travel effects, and provide coverage. Pearls are used in many cosmetics including nail polish, eye shadow, lipstick, and blush. The adjective nacreous is derived from nacre, which is pronounced NAY-ker. It refers to the material that makes up pearls and the iridescent mother-of-pearl produced in mollusk shells.

Several types of cosmetic pearls are available based on different substrates like mica, guanine, bismuth oxychloride, calcium sodium borosilicate, and fluorophlogophite. Each substrate has it’s own advantages and disadvantages.

Mica

More formally, cosmetic micas are postassium aluminum silicate dihyrdrate. Silicates, much like silica, are based on interconnected SiO4 tetrahedra. (Yes! I finally got to use the word tetrahedra in a blog post!) However, in silicates the ratio of Si to O is greater forming silicone-oxygen anions. To form neutral solid silicates, cations like potassium are needed to balance the negative charge. There’s a great deal of hype around so-called natural mineral make-up cosmetics.

Although mineral by definition, the distinction of natural is pretty much out of the question in my opinion. The amount of processing and refining needed to make theses ingredients cosmetically acceptable, furthermore the processes and reactions used to deposit color on mica for matching various skin tones or to create other colorful effects make it pretty silly to imply they are anything close to their natural state. Naturally derived, sure, but then so is petrolatum… I digress. Micas are subject to size restrictions; particles are not to exceed 150 ?m. Other substrates are not specifically regulated for particle size.

Guanine

Guanine, a common biological molecule, is derived from fish scales and provides a soft pearly shimmer. It is the photonic crystalline structure of guanine that scatters and reflects light to produce the pearl effect. Cosmetic grades are, of course, purified and often dissolved in a suitable solvent for ease of handling. Although this might qualify as a true natural pearl, cost is often prohibitive.

Bismuth Oxychloride

Though more frequently used as a filler in cosmetic formulations, bismuth oxychloride provides a silvery, white tone. The various particle sizes available allow for different levels of transparency, however larger crystal forms are supplied as dispersion because these larger crystals can be broken in their dry form.

Calcium-Aluminum Borosilicate

Because this substrate is highly transparent, brilliant sparkle effects can be achieved. This also suits clear formulations where effects are desired with less opacity. But the cost is typically more than traditional micas.

Fluorophlogophite

Referred to as synthetic micas, fluorophlogophites are one of the newest innovations in pigments having been on the market a relatively short period of time as far as cosmetic ingredients go. Unlike mica which carries natural impurities along with it, the synthetic version is clean and transparent. This allows for more brilliant sparkles effects.

In the second part, I’ll talk more about the physics of these compounds and how they can be made to produce different colors.

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