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II. The middle zone of a flame is yellow. It is bright and luminous. The fuel burns partially in
the middle zone because there is not enough air for burning in this zone. The partial
burning of fuel in this zone produces carbon particles. These particles become hot and
emit light.
III. The outermost zone of a flame is blue. It is a non-luminous zone. In this zone, complete
combustion of the fuel takes place because there is plenty of air around it. This zone has
the highest temperature in the flame. The goldsmith uses a blower to blow the outermost
zone to melt gold and silver.

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