Researchers aren’t cleaning up spilled black coffee but are instead studying the stain left behind to help improve images from printer ink processing.

The splashes from black coffee on a desk or other surfaces dry into ring-shaped stains. In comparison, spilled sweet coffee leaves uniform stains without an unevenness.

The Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has published research results on the mechanism behind that phenomenon. That finding could be used to help suppress unevenness in printer output if it is applied to ink processing, JAMSTEC officials said.

JAMSTEC is a national research and development agency in charge of ocean exploration and other activities.

“Particles are contained in various liquids that exist in nature, such as raindrops and wave splashes,” said Shunsuke Shimobayashi, a JAMSTEC scientist who was part of the research team. “I hope the results of our latest study will help elucidate their movements.”

The agency’s latest study showed that a drop of black coffee evaporates mainly near the edge, so liquid moves outward from the drop center. Coffee particles are also carried outward, so they stay and leave a ring-like stain when all the liquid has dried up.

The study showed, on the other hand, that adding sugar to the coffee suppresses the outward movement of the liquid, thereby working against the formation of a ring-shaped stain, the officials said.

The “coffee ring effect,” whereby liquids containing particles dry into ring-like stains, can cause unevenness in inkjet printer output. The latest research results could be used to provide an easy means for suppressing similar unevenness, the officials added.

The research results were published online Dec. 11 in Scientific Reports, a British science journal.