Glossary
Whitening
Also called: edge whitening, corner whitening, card whitening
Whitening is the pale line that appears along a card's edges or corners when the printed surface layer wears away and exposes the lighter core beneath.
Trading cards are layered stock. The coloured print sits on the outside; the middle of the card is a lighter core. Any abrasion that removes the printed layer at an edge reveals that core as a white line.
It shows worst on cards with dark borders, which is why heavily bordered sets are harder to keep looking clean than white-bordered ones. The wear is identical; the contrast is not.
Whitening is a grading problem as much as a cosmetic one. Grading criteria hinge on corner sharpness and edge condition, so visible whitening puts a ceiling on the grade a card can reach regardless of how good the rest of it looks.
It is caused by handling and movement, which is why a holder that lets a card shift around can create the exact wear it was bought to prevent.