The British Library is to extend a ban on pens to all its reading rooms to protect its precious collections.
Pens are already banned in several reading rooms
From January, the home of the Magna Carta and Lindisfarne Gospels will only allow pencils.
Marks made with ink are difficult to remove and sometimes defaced books have to be withdrawn from use, a library spokesman said.
The pencils-only rule applies to all reading rooms at St Pancras in central London and Boston Spa, West Yorkshire.
The spokesman said: "This policy is intended to protect the most precious and vulnerable collections that ink can cause.
"Marks made with ink are particularly difficult to remove and sometimes defaced books cannot be replaced and have to be withdrawn from use."
Pens have already been banned from the library's Rare Books and Music, Manuscripts, Maps, Oriental and India Office and Philatelic reading rooms.