History of Clean-Slate phrase

Clean slate comes from the time people wrote on (slate) chalk boards. Whether that was your tavern bill or your letters in school. Starting with a 'clean slate' meant you wiped the board clean and started over.

Clean slate comes from the slate boards used in schools. The expression is used figuratively from the mid. 19th century.

• A fresh start; another chance after wiping out old offenses or debts. This idiom often appears as wipe the slate clean. For example, Henry's boss assured him that the matter was finished and he could start with a clean slate, or He wished he could wipe the slate clean, but it was too late to salvage the relationship.

• This expression alludes to the slate boards on which school work or tavern bills were recorded in easily wiped-off chalk. Since 1850 or so the term has been used figuratively, and it has long outlived the practice of writing on slate.

(AHD)

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