Each bell, when born, lives its own life. For instance, the Royal (Tsarsky) and Svyatitelsky bells at Christ the Savior Cathedral at first lacked purity of voice. But with time, they tend to "calm down", as bell-ringers say. In Rostov Velikiy, there are bells named "Goat" and "Ram", which were born with the voices their names suggest. The strike tone and various overtones, undertones, and partials of a bell should all peal as a chord, but Goat and Ram bleated however they chose. In Trinity-Sergius Lavra, it took a long time for another bell to calm down, which stood out from the choir and for its ambitiousness, and had received the name, "Arguer". Also well known for its unconcern is a bell named "Wayward" [Bezsputniy, which might even suggest a "wayward woman"].
If a bell does not cool uniformly, the metal will develop internal tensions that will distort the sound. However, bell-ringing vibrates the metal's crystalline structure and over time the tensions can settle down and the bell mellow out.