On a radiograph, excessive joint penetration appears as a _________ line.

Excessive joint penetration on a radiograph is characterized by a light line. This occurs because the excessive penetration of the weld root into the base material results in a greater density of the weld area. In radiography, denser materials absorb more radiation, leading to lighter appearances on the radiograph. Therefore, areas of excessive joint penetration will appear lighter compared to the surrounding areas that are correctly welded.

This contrasts with areas that are undercut or exhibit insufficient penetration, which may appear darker, as these regions have less material density. Understanding the visual characteristics of different weld defects on radiographs is essential for accurately interpreting the quality of welds during inspections.