What causes sharp, black, bird-foot shaped marks on radiographs that do not correspond with any discontinuities?

Sharp, black, bird-foot shaped marks on radiographs that do not correspond with any discontinuities are typically caused by static charges generated through friction. When film is handled in a manner that creates friction—such as when it is pulled from a film holder or when it rubs against other surfaces—static electricity can build up. This static can discharge onto the film during exposure or development, creating these distinctive marks.

These bird-foot shaped artifacts appear because the static charge attracts the developing chemicals or the beam of radiation differently than the surrounding film. Consequently, while the radiograph appears to have these sharp marks, they do not correlate to any actual features of the material being examined. Understanding this phenomenon is important for radiographers, as it emphasizes the need for proper handling and storage of film to minimize static electricity and related artifacts, ensuring clearer and more accurate results.