The branching needles in this polarized-light micrograph are crystals formed by evaporating drops of a Swiss sauvignon wine. The gold and blue colors are interference colors produced under polarized light. The patterns help visualize the crystal’s growth morphology and branching geometry.
As grapes ripen, they produce tartaric acid, which wine carries, along with potassium absorbed from the soil. As the wine drop evaporates, the dissolved components become increasingly concentrated until the system reaches supersaturation. The potassium ions and hydrogen tartrate then precipitate as potassium bitartrate—the compound that settles as sediment at the bottom of unfiltered bottles. The branching structure reveals that these crystals formed out of equilibrium: the wine drop evaporated too quickly for the crystals to grow in an orderly fashion. Slow crystal growth lets molecules arrange layer by layer. But when evaporation outpaces growth, new material builds at the edges and tips, splitting the branches into finer needles in a process called dendritic growth.
Hélène Lambert, a third-year chemistry student at the University of Geneva and founder of the scientific design project Helnium, photographed these crystals as part of a study comparing how different liquids crystallize when left to dry on a slide.
Submitted by Hélène Lambert.
