What is the purpose of the milky stage of flux?

The purpose of the milky stage of flux is primarily to indicate that the flux is ready to use. When the flux reaches this milky or opaque appearance, it signifies that it has been properly heated and is effective for the brazing process. At this stage, it has a consistent and active composition that can adequately protect the metal surfaces from oxidation, facilitate the flow of the filler metal, and improve overall joint integrity during the brazing process.

The milky stage is an essential visual cue for the technician, as it reflects the right temperature and the chemical changes that allow the flux to perform its intended functions effectively. Recognizing this stage ensures that the operation proceeds with high-quality results and minimizes the risk of issues occurring during brazing.