246 SCIENTIFIC AMUSEMENTS. 



of engraved copper rollers (Expt. 272), in such a fashion that the 

 pattern ultimately to appear in colour is first applied to the calico 

 in the form of a nearly colourless fluid. The mordanted goods are 

 then usually put through a process of exposure to air heated by 

 the admission of steam, termed ageing, which fixes the metallic 

 compound more firmly on the fibre by virtue of chemical changes 

 brought about by moderate heat and moisture ; after which they 

 are passed through the bath of dyestuff dissolved in water, when 

 the colour is absorbed and fixed on the cloth at those spots where 

 mordants have been applied, but not elsewhere ; so that, finally, 

 when the cloths are well washed and "cleared," the colouring 

 matter is entirely removed from the body of the fabric, but is 

 retained at the mordanted spots, thus developing the pattern. 



One and the same dyestuff can be made to give a variety of 

 colours and shades by suitably varying the nature of the mordant- 

 ing material, and the quantity of it used relatively to the water, &c., 

 added to dilute it in preparing the fluid printed on to the cloth by 

 the rollers ; thus mordanting solutions of acetate of aluminium 

 will give various pink and red shades (according to the strength) on 

 calico passed through a dyebath containing the colouring matter 

 of madder (either that from the natural root or the artificial 

 alizarin now manufactured from coal tar) ; whilst acetate of iron 

 similarly yields shades varying from pale violet and lilac to a very 

 dark purple almost blue black ; and mixtures of these compounds 

 together (or with other analogous metallic salts) will give clarets 

 and other shades. By engraving a portion of the total pattern on 

 one roller, another on a second, and so on, up to five rollers ; and 

 supplying the first roller with, say, a weak solution of acetate of. 

 aluminium, and the second with a stronger one ; the third with a 

 weak solution of acetate of iron, and the fourth with a strong one, 

 and the fifth with some appropriate mixture of salts ; it becomes 

 possible to produce a pattern with five distinct colours by one 

 immersion only in the same dyebath; the portions of cloth 

 mordanted by the first roller becoming a light red, and those by 

 the second a dark red ; those by the third a light violet, and those 

 by the fourth a dark purple ; and those mordanted by the fifth 

 roller some other colour. Similarly, patterns in more than five 

 colours can be prepared by suitably multiplying the rollers and 

 varying the mordants. 



Pieces of calico thus prepared with a variety of different 

 mordants can be purchased from dealers who supply materials for 

 chemical lecture experiments, as also can alizarin and various other 

 dyestuffs ; the process of making and applying the mordant and 

 subsequently dyeing may be roughly imitated on the small scale 



