When you think of fluorescence you think of terrible, garish paper or clothing. But plenty of fluorescence can be found in nature, and sometimes it can be used to check what's purely natural. You can start in your very own kitchen, with olive oil - make it glow like it's radioactive with this easy experiment.
Fluorescence is a slight quirk on how light generally works. Most often a photon is absorbed by an atom and emitted again at the same energy level as before. A fluorescent object will take in light at one energy level, and spit it out at a slightly lower level. Often the fluorescent objects that we're sold will absorb ultraviolet light, which we can't see, and then re-emit it as visible light, seeming to glow on their own.
Ultraviolet light isn't needed to make things fluoresce. Olive oil, though it's dull under regular light, is a fluorescent substance. Hit a clear glass of olive oil with a green or blue-violet laser. If you choose a laser with a wavelength of 405 nanometers, the oil should glow red. A 532 nanometer beam will make it glow orange.
It's not just lasers that will get the olive oil to fluoresce. Hitting it with ultraviolet light, a black light, will make it fluoresce a bright yellow color. That is, it will be yellow if it's pure olive oil. A lot of olive oil is adulterated with cheaper vegetable oils; if more than five percent is some other oil, it will glow blue under black light. Unearth your old black light and do some quality control checks in your kitchen. Or just find a laser and make your oil glow.
Image: Leon Brocard