How did the Bell become cracked in the first place

A casting flaw. It spread after its initial use and did under go repairs over time but eventually was preserved in its currently cracked state

The Crack  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 1840's after nearly 90 years of hard use. In 1846, when the city decided to repair the bell prior to George Washington's birthday holiday (February 23), metal workers widened the thin crack to prevent its farther 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! Look carefully and you'll see over 40 drill bit marks in that wide "crack". 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.  Copied from NPS website

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