When Bismuth was first mentioned, it was said that she and Amethyst became friends as soon as Bismuth was built.
Later, Bismuth was seen talking to her best friend, Topaz, about how much she wanted to go to Sodor, but she wasn't aloud. Topaz told her to take some gems to Sodor anyways, so Bismuth took the train that Amethyst was going to. However, on the way to Sodor, Diamond, Jasper, Aquamarine, Holly Blue, and Malachite started playing tricks, and Bismuth ended up having an accident.
Bismuth is friendly, boisterous, fierce, determined, empathetic, and emotive. She is not afraid to speak and act her mind. She also cares deeply for her friends. She is also slightly naive, as she is the youngest engine on Crystal Island.
Bismuth is based on a BR Standard Class 9F, which were used for fast and heavy goods trains. The class was the last of the BR Standards and the final steam engine class built by British Railways, with the last one, "Evening Star", built in March 1960. Due to the size and shape of the class, they where given the nickname "Spaceships." "Evening Star" and eight other 9Fs are preserved. One 9F, "Black Prince" holds the record for hauling the heaviest steam-hauled train in Great Britain, at 2,198 tons. "Evening Star" is also part of the National Collection. Murdoch, Marie, and Blue Diamond are also members of this class.
Bismuth's original design featured added trailing wheels and a Fowler tender. It also lacked smoke deflectors. However, her design became more accurate to her basis upon her redesign.
Originally, Bismuth is painted lavender with rainbow colored lining and wheels. She also had a dark purple cylinder and dome. She had pink tender lining and a pink bufferbeam/footplate. She had her number in black inside a pink star on her tender, along with her rainbow colored gemstone.
Currently, Bismuth is painted mauve with rainbow colored lining and wheels. She has her number in black on her tender, along with her rainbow colored gemstone. Her tender has pink wheels and her cab and cylinders also have pink lining. She also has dark grey smoke deflectors.