[CHAPTER X]
THE DYEING AND COLOURING OF PAPER PULP
Nearly all papers, even those commonly regarded as white, are dyed with some proportion of colouring matter. With the ordinary writing and printing papers the process is usually confined to the addition of small quantities of pigments or soluble colours sufficient to tone the pulp and correct the yellow tint which the raw material possesses even after bleaching. In the case of cover papers, tissues, and similar coloured papers, the process is one of dyeing as it is generally understood.
The colouring matters which have been employed by the paper-maker are—
Pigments.
(A) Added to the pulp in the form of mineral in a finely divided state.
Yellow.—This colour is obtained by the use of ochres, which are natural earth colours of varying shades, from bright yellow to brown.
Red.—Ordinary red lead.
Various oxides of iron, such as Indian red, Venetian red, red ochre, rouge.