Repurposing pencil lead as an optical material using plasma

Optical materials are essential in many modern applications, but controlling the way a material reflects light on its surface is costly and difficult. Now, in a recent study, researchers from Japan found a simple and low-cost way of tuning the reflectance spectra of pencil lead samples using plasma. Their technique enabled them to produce pencil lead with various structural colors and even print invisible characters that can only be seen using an infrared camera.