For silver soldering, what is the purpose of using flux?

• A. It seals the joint to moisture.
• B. It is used to remove oxides and chemically clean the base metal.
• C. It increases the solder's melting point.
• D. It helps the solder flow into fine gaps.

Answer: (B)

Flux is used to remove oxides and chemically clean the base metal, which is essential for a strong bond in silver soldering. Oxide films on metal surfaces act like a barrier to solder wetting, so flux chemically dissolves or reduces those oxides and keeps the surface clean as the joint heats. This clean surface allows the solder to wet and flow into the joint, creating a good bond. Flux does not seal moisture or raise the solder’s melting point; its primary role is oxide removal and surface preparation to enable proper flow and adhesion.