The exterior walls of the Toto Research Institute in Chigasaki, Kanagawa Prefecture, look like patchwork; some square areas are dark with stains while others are spotless.
"The clean parts are coated with a paint using photocatalytic technology," said Yoshimitsu Saeki, general manager of the institute, which is operated by Toto Ltd.
Saeki said this process is caused by the self-cleaning effects of titanium dioxide photocatalysis -- the chemical reaction between titanium dioxide and sunlight, known to researchers as the "Light Cleaning Revolution."