Ice had formed on the outside of the ship, and the crew was chipping it off.
船的外面结了冰,船员们正在把它削掉。
BBC纪录片《百件藏品话沧桑》
They look like chipped cobbles, and they were made simply by taking one large piece of stone and striking it with another, chipping off a few bits to make at least one sharp cutting edge.