Why do goldsmiths use the outermost zone of the flame for melting gold and silver?

Explanation

Goldsmiths, use the outermost zone or non-luminous part of the flame for melting or shaping gold and silver ornaments. They direct the non-luminous part of the flame of candle on the gold with the help of a blow pipe. The temperature of this part of the flame is around `1300^(@)C`, it is sufficient to melt gold at specific point, and thus helps goldsmiths to give proper shape to the gold ornaments.