Most paper used for commercial advertising, vintage or otherwise,
is cheap and disposable – often with high acidic content.
One of the ways to strengthen and naturally preserve paper
is to mount it to an archival acid-free surface, a process
often referred to as “Linen-backing”. In fact, a misleading
description since no linen is used. The term dates back to
an early 20th century French process for conserving posters.