There are more than three physical characteristics provided in the description of the blacksmith. The poem states that he is "a mighty man"; that he has "large and sinewy hands"; that he has "brawny arms" with muscles like "iron bands." He has long, dark hair and a good tan, and his face is wet with the sweat that comes from hard physical labor.
Digging a little deeper, the blacksmith's appearance is open and direct. He can walk upright and proud because he earns his daily wages by doing his daily work. He treats all people honestly and worthily, which allows him to approach his life without a frowning or angry expression. While there is some sorrow and regret that his wife is no longer alive with him, he is carrying on and making a good life for himself and his children, and his physical appearance probably reflects that it is a struggle, but that he is succeeding.