Scientist rinsing mud from sample tubes beside stream

Indigo twilight washes over a tightly cropped view where gloved hands hold a ceramic sample tube beneath a thin stream of clear water. Dark, wet mud slides from the tube's rim, swirling into the darker flow of the river below. The ceramic surface shows a matte, earthy texture, against the slick, reflective water. Behind the hands, blurred city lights begin to glow through the indigo air, hinting at Changsha's urban edge. Overhead, dramatic clouds stack in heavy layers, filtering the last natural light. The water droplets clinging to the tube's edge catch the faint glow of the distant city, marking the precise moment of rinsing.