Book said the ledger paper dating back to the 1800s is so fragile the pages can't be studied without causing further damage.
From the upi.com
This includes ledger, bank, and bond paper.
From the en.wikipedia.org
Ledger art is a term for Plains Indian narrative drawing or painting on paper or cloth.
From the en.wikipedia.org
The term comes from the accounting ledger books that were a common source of paper for Plains Indians during the late 19th century.
From the en.wikipedia.org
Due to the scarcity of hides, Plains artists adopted new painting surfaces, such as muslin or paper, giving birth to Ledger art, so named for the ubiquitous ledger books used by Plains artists.