Cleaning windows can reveal that glass once thought discolored was merely dirty.

Evidence

I have cleaned all the windows, which, ever since I have been here, I supposed were of discolored glass, so opaque and dirty they were; and when the men came home from fishing they found a cheerful new world. — Isabella L. Bird, A Lady’s Life in the Rocky Mountains, 245

Categorization

• CANDY: The whole party had accepted grimy panes as bad glass until someone washed them — a lovely small-scale revelation.