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CHAPTER II.

MINERAL PIGMENTS.

, \^7’E shall under this head have occasion to revert to some mineral salts,which we have treated elsewhere with other views ; the re-statementhere is necessary when we specially regard the mineral as a pigment.

Every mineral colouring matter that is insoluble in water, and reduced toan impalpable powder, can be applied to woven tissues by means of plasticsubstances, such as albumen. Every mineral colouring matter insoluble inwater, and capable of development upon textile fabrics by soluble substances(that is to say, by precipitation), can be employed in the processes of dyeingand printing. Practically, however, the number of mineral pigments islimited. Various reasons can be given for the large number of exceptions.Leaving out of consideration the question of cost, there are such desiderataas brilliancy, resistance to the influence of light, atmospheric and chemicalaCtion, difficulties in fixing certain colours, and, finally, the danger of poisoningas a consequence of the use of certain pigments. As mineral colours varylargely in composition and character, it will be unsatisfactory to give a generalreview of their properties, but will be better to treat them specifically. As toclassification, the pigments may be separated into as many divisions as thereare colours in the speCtrum, and further into groups according to their chemicalrelations. The means and methods employed in fixing these materials uponwoven tissue will be separately described for each particular substance.

WHITE COLOURING MATTERS.

To these belong, in a very limited sense,—

Chalk, or Carbonate of Lime.

Used as an oil-paint for in-door work, and as a water-colour when mixedwith gelatine. Chalk is sometimes employed to dilute other pigments,—thatis to say, to modify the shade, as with chrome-yellow and orange, ultramarine,and Brunswick green. Prepared chalk is used in manufacturing chemistry forthe purposes of saturating acid fluids. It is not used as a pigment in dyeingor printing.

Sulphate of Lime, or Gypsum.

Perfectly white plaster-of-paris (so called because the geological formationupon which Paris stands is very rich in gypsum) is of only limited use as apaint in the manufacture of paper-hangings, being then mixed with gum-water.It is not employed as an oil-colour, and does not find any application inpigment-printing.

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