Which characteristic indicates an improperly soldered joint primarily due to insufficient solder?

The characteristic that indicates an improperly soldered joint primarily due to insufficient solder is the presence of shiny areas. In soldering, a properly made joint should have a uniform and consistent appearance, demonstrating that the solder has adequately flowed into the joint and created a solid bond.

When the solder is insufficient, shiny areas may form where the solder has not properly wetted the surfaces of the pipe or fitting. These shiny spots usually result from a lack of sufficient solder filling the joint, which compromises the integrity of the connection and indicates that the soldering process did not achieve the necessary penetration and adhesion.

In contrast, visible gaps would suggest a lack of alignment or improper fit, while smooth texture can indicate a well-made joint. Uneven edges might reflect poor cutting or fitting of the pipe but do not specifically point to the solder's sufficiency. Shiny areas, therefore, are a telltale sign that the joint is not adequately secured due to insufficient solder application.