The Eberhard effect is a border phenomenon in photographic development, appearing as a dark line along the edge of a high-density area and a light line along the edge of a low-density area. It typically occurs when plates or films are developed flat in a solution that is not adequately agitated.
This effect, first described by Gustav Eberhard in 1926, highlights the importance of consistent chemical movement during development. Proper agitation helps prevent uneven development, ensuring smooth tonal transitions and avoiding unintended lines or borders in the final image.