Top pic: Ice cubes (left) and leftover uranine solution from when I was preparing those ice cubes Bottom left pic: Melting the ice cubes in a water bath to see if they start glowing again when melting. Bottom right pic: Yes, they do! :-)
Why do I find this exciting? Because that means that a phase change of the water switches fluorescence as a tracer of that water on and off. Or the other way round: Seeing water fluoresce (or not) tells you what state the water is in without having to figure out anything else about that water.
…and funny how that the apprenticeship as chemical technician that I started in parallel to finishing high school (and didn’t finish because other stuff — oceanography — became more interesting) does come into play in the most unexpected moments :-)
I had frozen a second tray* with ice cubes dyed with uranine (you know, the green stuff I found in the lake near my house the other day?). Like the other ones, they clearly froze back-of-the-freezer-forward, and the most interesting thing to me: Only the parts that weren’t frozen were fluorescing in the fridge!
For comparison, here a picture of the leftover water (so same dye concentration as the ice cubes) in the beaker, and the tray with frozen ice cubes next to it. You can see the beam of the UV lamp on the table* so you believe me that the ice cubes were lit with UV light, too, they just don’t fluoresce!
*Ailin and Steffi, did you see I got you a gold colored ice cube tray? :D Although, had I thought that I would be looking at the ice cubes themselves this much, I would probably have gotten two whites instead of a white and a gold one… But now you at least have a pretty ice cube tray in the lab :-)
**and a stain that I am only now noticing, but it wasn’t me; I was working super carefully since today I am not dressed for the lab and I don’t want that stuff on my clothes!