A while back I bought these “engravable sandstone coasters” as I was binge-purchasing things I might want to stick under the laser beam. They’re definitely engravable, but without doing any extra work the result is a pretty low-visibility white on white (the camera actually makes it look better than real life):
Last night I was playing around with a blacklight for future florescent acrylic applications, and I happened to shine it near the coaster. Suddenly, contrast!
That’s all, really. Just sharing an interesting special effect with little practical value.