James McNeill Whistler’s 1871 painting best known as “Whistler’s Mother” depicts an unsmiling matriarch locked forever at age 67, eyes failing, ailing in a damp city, bad teeth hidden behind a set jaw.

Over the years, this mother has been a symbol of either the caregiver who nurtures her children or the grump who raps their knuckles. An exhibit opening Saturday at the Clark Art Institute in Williamstown, Mass., explores Anna McNeill Whistler’s migration from patriotic emblem of American motherhood to comically stern pop-culture icon.