The Manufacture of Paper / With Illustrations, and a Bibliography of Works Relating to Cellulose and Paper-Making

by R. W. Sindall

(b) Basic dyes, so called because the colour is best developed in an alkaline solution, without any excess of mordant.

(c) Substantive dyes, which do not require the use of a mordant, as the colour is fixed by the fibre without such reagents.

Some of the most frequently used colouring matters are shown in the accompanying table on page [202].

The distinction between acid and basic dye-stuffs is largely due to certain characteristics possessed by many of them. Thus magenta, which is the salt of the base known as Rosaniline, belonging to the basic colouring matters, a group of dyes which do not possess the fastness of colour peculiar to acid dyes, has a limited application. But by treatment with sulphuric acid magenta is converted into an acid magenta, and this dye has wider application than the basic salt. Similarly the basic dye called aniline blue is insoluble in water, and therefore has only a limited use, but by treatment with sulphuric acid it is converted into alkali blue, soluble blue and so on, which dissolve readily in water and are good fast colours. The acid dyes generally have a weaker colouring power than the basic dyes, but they produce very even shades.

Colour.	Acid.	Basic.	Substantive.
Yellow	Metanil yellow.	Auramine.	Cotton yellow.
and	Paper yellow.	Chrysoidine.	Chrysophenine.
Orange.	Orange II.
	Naphthol yellow S.
	Quinoline yellow.
Red.	Fast red A.	Rhodamine.	Congo red.
	Cotton scarlet.	Paper scarlet.	Benzopurpurin.
	Erythrine.	Safranine.	Oxamine red.
	Ponceau.	Magenta.
Blue	Water blue 1 N.	Methylene blue.	Azo blue.
and	Fast blue.	Victoria blue.
Violet.	Acid violet.	New blue.
		Indoine blue.
		Methyl violet.
		Crystal violet.
Brown	Naphthylamine brown.	Bismarck brown.
		Vesuvine.
Black	Nigrosine.	Coal Black B.
	Brilliant black B.
Green		Diamond green.
		Malachite green.

The difference in the composition of the basic and acid dyes is taken advantage of in the dyeing of paper pulp to secure a complete distribution of the colouring matter upon the pulp, with the result that the intensity of colour is increased, its fastness strengthened, and the process of dyeing generally rendered more economical. This is effected by the judicious addition of a suitable acid dye to the pulp already coloured with the basic dye.

The direct colouring matters have but a very limited application for paper dyeing owing to their sensitiveness to acids and alkalies.

In the colouring of paper pulp, attention is given to many important details, such as:—

Fading of Colour.—Some loss of colour almost invariably occurs even with dyes generally looked upon as fast to light. The shade or tint of the paper is affected not only by exposure to light, but by contact of the coloured paper with common boards on which it is often pasted. The alkalinity of straw boards, for example, is frequently one source of serious alteration of colour, and the acidity of badly made pastes and adhesives another.