w o r k e r - 6 letters
A metallurgist is the twelve-letter word for a worker in metals.
smith
welder
Farrier is connected to the word ferro, metal. Horse shoes are made of metal A farrier in olden times was also the blacksmith, the worker of metal.
hand
The word operative is defined as functioning or having effect. An operative can also be be a skilled worker, specifically in the manufacturing industry.
metal
gold
tins
Gold.
Metal
Ore