On a radiograph, porosity appears as __________ spots.

Porosity appears as dark spots on a radiograph due to the way X-rays interact with materials. In welding and other metallurgical contexts, porosity refers to tiny gas pockets or voids that can form within the weld metal. Since these voids are less dense than the surrounding metal, they allow more X-rays to pass through when examined on a radiograph.

The X-ray film captures this difference in density: areas where X-rays penetrate more and reach the film appear darker, while denser material blocks more X-rays, resulting in lighter areas. Consequently, the presence of porosity will show up distinctly as dark spots, allowing weld inspectors to identify potential defects in the weld. Understanding the interpretation of radiographs is crucial for assessing weld quality, and recognizing these patterns helps ensure structural integrity in welded components.