Coal Hill School tie

The official Coal Hill School tie was black with thin, diagonal, emerald green stripes.

History
The First Doctor once used Ian Chesterton's Coal Hill School tie to test whether a pool discovered on the planet Vortis, in which Ian was about to wash his hands, was acid instead of water. The test was positive, so the tie disintegrated. Ian was perturbed at the loss of the familiar object, until he understood that the test had saved his life. (TV: The Web Planet)

Years later — at the dawn of the 21st century according to one account — an older Chesterton encountered a stranger while walking in London. They had a brief and enigmatic discussion about the nature of time, and then Chesterton continued on his way. When he arrived at home, his wife Barbara said that a strange man had left him a package. When Chesterton opened the package, he discovered a brand new Coal Hill School tie. (PROSE: Untitled)

By the 21st century, the Coal Hill School tie was worn only by students as part of the uniform, and the colours changed to equally thick silver-white and blue stripes. (TV: The Caretaker)