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DYEING AND CALICO PRINTING .

indigo solution. Thus the required shade can be obtained with the smallestpossible number of dips. This vat gives shades more solid and clear than canbe obtained with the old vats, and enables the dyer to produce upon wool verylight blue bottoms, which are ordinarily got by means of sulphate of indigo,and are in consequence much more fugitive. The authors propose to printwith an alkaline solution of reduced indigo, suitably concentrated andthickened, containing a large excess of hydrosulphite of soda. The presenceof this salt tends to keep the indigo-blue reduced, which otherwise tends tobecome oxidised during the time of printing. This part of the process can becarried out in common air, and with an ordinary machine, the oxidation beingso slight that after an hour’s work the remnant of the colour is still yellowand soluble. By thus printing on reduced indigo immediate fixation issecured, and the entire colouring matter is utilised. Experience has provedthat, for equal shades, 50 to 60 per cent less indigo is consumed with the newprocess than with the old. The shades obtained are more beautiful and solid,and the impression is better defined. The new indigo-blue, requiring no sub-sequent fixing process, can be printed along with a great number of othercolours, such as aniline black, garancin, colours obtained by dyeing orsteaming, catechu shades, chrome colours, colours fixed with albumen, &c.Thus new styles may be created which would be difficult to execute in anyother manner. The blue printing colour is formed by thickening, with gum orany other suitable material, a sufficiently concentrated solution of white indigoin an alkali, and adding to the mixture a sufficient quantity of hydrosulphiteof soda. After printing, the pieces are hung up for twenty-four hours tooxidise, washed, and soaped.

We have now to consider the methods of fixing indigotin in printing, aprocess solely applied to calico. The pencil-blue style dates back certainlyninety or a hundred years, and no improvements have been made upon itsince the commencement.

Pencil-blue consists of reduced indigo, and is made by heating a mixtureof finely-ground indigo, orpiment, and potash. These latter substances forma powerful deoxidising mixture, which speedily reduces and dissolves theindigo. In a short time after mixing, the blue colour of the indigo disappears,and gives way to a yellow, except at the surface, where the oxygen of the aircontinually revives the indigo, causing it to assume a coppery-blue. Theavidity of this mixture for oxygen, whereby the indigo is restored to its blueinsoluble state, is so great that it cannot be exposed a moment to the air withoutbeing covered with a scum or pellicle of blue indigo, and it is also the cause of thegreat difficulty in applying pencil-blue in a regular and satisfactory manner. Assoon as the block or roller leaves the colour, and enters the air, the surface ofthe colour is covered with a scum of indigo, which, being insoluble itself, can-not enter the fibre of the cloth, and, lying on the surface of the soluble colour,is a hindrance to its entering into the fibre. Peculiar arrangements have to bemade in applying this colour to prevent contact with the air; they are allmore or less defective, and the results are often irregular. In the old methodof applying it with a pencil, the pressure upon the fibres of the pencil (thisconsisted of a piece of willow-wood stick, which, by means of a blow givenwith a mallet on one of the ends, was somewhat split and splintered into a