Generally speaking, the white paper we use is fiber pulp formed by processing tree fibers in a paper mill, which is laid flat on a flat plate and dried. But you can imagine the color of the cross section of the trunk. Wood fiber is slightly yellow, so paper is bleached with sulfur dioxide in industry. However, the bleaching of sulfur dioxide is not as stable as chlorine, and it is easy to be oxidized into sulfuric acid by oxygen, which loses the bleaching effect. In this way, the color of wood fiber itself is exposed.

Sulfuric acid will destroy the fibers in the paper, so the paper will become brittle. In addition, if the paper is too dry, the lignin in the paper will be oxidized, which will also lead to fiber breakage and make the paper brittle.

The traditional paper-making industry in China uses some trees with relatively white wood fibers to make paper, such as ebony, the raw material of rice paper. So many ancient books can be preserved for thousands of years without being bad.