If you are a lady, you have probably at one point slathered your lips in fish scales. (If you are a gentlemen, you have probably pressed your lips against those scales.) Why? Because it looks pretty. And because of physics.

To understand why fish scales were first used in makeup, we have to understand why they were used outside of makeup. In past centuries, respectable ladies may not have worn makeup, but they did wear jewelry. How frustrating then, that they often found that they could not afford jewelry. Help was on the way: Clever proto-materials scientists found that they could use fish scales to simulate pearls.

Pearls have a kind of scattered radiance to them, as if they are being lit from within. That’s because they are – especially when fake ones are made by coating ordinary beads with fish scales. The scales are made from purines, which are the things that also make up nucleic acids. The purines are arranged in a crystal that’s both flat and irregular, like the shards of a window pane. When groups of them are arranged over each other, as light hits the plane of each crystal, some light is reflected back, and some keeps going down until it hits another crystal. As light gets thrown up, in a diffuse way, from many different levels, the scales seem to emanate light from within. Slather enough layers on a bead, and it has a glowing, pearlescent quality.

If it works on a bead, it must do the same for lipstick. Pastel, pearlescent lipsticks have gone in and out over the years. The ingredient used to make them hasn’t. These crystals do the same thing they do one fake pearls (and real fish): They reflect light from many different angles and levels, making lips seem to shimmer with an inner light. Fish scales may not be a romantic ingredient, but they are available and nontoxic. Considering it wasn’t that long ago that some lipstick brands were found to be contaminated with lead, a little fish doesn’t sound that bad.

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Top Image: Tania Saiz, Second Image: Daisy Romwall

[Sources: Pearl Essences: A Specialty Chemical Product , Cosmetics and Skin]