Why do goldsmiths use the outermost part of the flame to melt gold and silver?

Goldsmiths use the outermost part of the flame to melt gold and silver because it provides a higher temperature while minimizing the risk of contamination. The outer flame is more oxidizing, which helps to keep the metals clean by preventing impurities from being absorbed. Additionally, this part of the flame allows for better control over the melting process, ensuring that the metals reach their melting point efficiently without overheating.