Researchers at MIT and Penn State University have discovered how ordinary droplets of water, when placed onto on a transparent surface, can produce brilliant structural colors without any dyes or additives. While this effect might appear to be similar to the natural formation of rainbows with round water spheres, it was discovered that these colors are actually made of water hemispheres. After this discovery, the scientists developed a way to predict how these colors will develop for possible commercial use.
The researchers have developed a model that predicts the color a droplet will produce, given specific structural and optical conditions. The model could be used as a design guide to produce, for example, droplet-based litmus tests, or color-changing powders and inks in makeup products.