I melted up some palm stearin, and wondered why it appears to have some bluish tint to it. Not as if it was, but more like
aerogel,
Cherenkov radiation, or
tonic water. Turns out that
palm oil is UV fluorescent. Illuminated with a black light tube, the palm stearin tabs glow in a bright aqua-blue. My first suspicion was that the candle manufacturers added optical brighteners to the palm stearin to offset a yellowish tint (just like common with laundry detergents and paper).
Next test: regular RBD palm oil (with a yellowish tint to it, out of suspicion for added fluorescent dyes) – glows greenish-blue too!
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Does this mean that soap with palm oil glows under UV light?
YES!
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Even better! This is my ZnO/TiO₂ lollipop swirl with 30% RBD palm oil. The swirl is hardly noticeable by eye, I had to increase the contrast on the left to make it visible at all. Its stripes without white pigment and those with the zinc white are glowing bright blue. But those stripes that happen to be brightest under normal light: the ones with TD:
don't fluoresce – no surprise that TD and its legendary UV absorption is a common ingredient in sunscreens.
The test with unrefined red palm oil was inconclusive; but as obscenely orange as this stuff already is, I'd have been very surprised anyway.
Who else has their soap under suspicion to glow under disco lighting, bank note counterfeit detector, or face tanner?