In melting gold, which part of the flame is recommended to use?

When melting gold, the recommended part of the flame to use is the reducing zone. The reducing zone is characterized by a fuel-rich environment where there is an excess of combustible gases. This environment helps in minimizing oxidation, which is particularly important for gold since it can oxidize if exposed to an oxidizing atmosphere.

Using the reducing zone allows for optimal heat transfer to the gold while preventing the contamination that can arise from unwanted reactions with oxygen or other elements. Consequently, this helps in achieving a clean melt, preserving the purity of the gold and ensuring that it retains its desired properties for casting or further processing.

In contrast, the oxidizing zone introduces more oxygen into the melting process, which can lead to oxidation of the gold. The neutral zone, while not harmful, may not provide the same level of control over oxidation as the reducing zone. The cooling zone is clearly inappropriate, as it is where the material would solidify rather than melt.