Recognizable for its crack, the Liberty Bell remains significant today for its message of liberty. No one recorded when or why the Liberty Bell first cracked, but the most likely explanation is that a narrow split developed in the early 1840s after nearly 90 years of hard use. In 1846, when the city decided to repair the bell before George Washington's birthday holiday, metal workers widened the thin crack to prevent its further spread and restore the tone of the bell using a technique called "stop drilling". The wide "crack" in the Liberty Bell is actually the repair job. But, the repair was not successful. The Public Ledger newspaper reported that the repair failed when another fissure developed. This second crack, running from the abbreviation for "Philadelphia" up through the word "Liberty", silenced the bell forever. No one living today has heard the bell ring freely with its clapper, but computer modeling provides some clues into the sound of the Liberty Bell.

Source: National Park Service