|Coffee Filter iridescence - Captured by Mendonça Jr at Cainã, Parana, Brazil. ©Mendonça Jr, shown with permission.
"I was in a hotel foyer yesterday and suddenly I observed this spectacular effect around a coffee filter seen through the door to the restaurant kitchen."
Water molecules evaporate from the hot liquid in the filter. They meet cooler surrounding air and condense to form small droplets. This is the 'steam' that we see.
With the right size and the right lighting there is brilliant iridescence as the droplets individually scatter and diffract light.
Compare with cloud iridescence.