The right or left markers for a radiograph are made of _______________, making them appear in bright white.

The correct answer is metal, which is used to create the right or left markers for radiographs because of its opacity to X-rays. When radiographs are taken, these markers need to produce a distinct contrast on the imaging film. Metal has a high density and effectively absorbs X-rays, resulting in areas that appear bright white on the developed image. This high visibility is crucial for accurately identifying the orientation of the radiograph, which is important for diagnosis and treatment planning.

Using materials like plastic, glass, or rubber would not provide the same level of contrast against the film, as they do not absorb X-rays as effectively as metal. Consequently, they would not create the pronounced white marking that is necessary for clear identification of the radiograph orientation.