to melt down ore to extract metal, or past tense of smell.
Old English 'smeltan' meaning to melt, from Proto-Germanic roots. Later specialized to the process of extracting metal from ore in smelters. The smell-related sense comes from the strong odors produced during smelting.
Medieval metalworkers literally had to burn their noses off doing this—the smelting process produces such toxic fumes that workers needed to position themselves carefully. This is why 'smelt' became the verb: the smell was so memorable it became the word for the whole process.
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