In the General Prologue to The Canterbury Tales, the Prioress is said to speak no oath stronger than "By Saint Eloi." Eloi, whose feast is celebrated on December 1, is the patron of goldsmiths. Though he was a bishop and successful evangelist, he was also an accomplished smith who made two thrones of gold with only enough gold for one. This was no miracle; he was just a skilled craftsman. Depictions still exist of some of his works -- chalices, crosses, tomb adornments, and the like -- but no extant work is known to be his (though many are claimed to be.
Two medieval depictions of him stand out. In one, he holds the Devil by the nose with a pair of pincers. In the other, he is shoeing a horse's hoof that he has removed from the animal. In that legend, he took the leg of the beast off, shod it, and then returned it to the horse.
Know any smiths? Wish them a happy St. Eloi's Day.