The idiom Dyed In The Wool is used to describe a person who is inflexibly fixed in their opinions. The first known reference to the phrase is in 1579. Its origins are in English wool mills and the fact that wool that had been dyed before it was treated would retain its colour much better than if it were dyed after weaving (which was known as “dyed in the piece”). Because of this, “dyed in the wool” came to be applied to anything that wasn't easily altered by other processes, such as persuasion.