INDIGO-VATS.

477

oxidising agent, such as dilute sulphate of copper, after which they only re-quire to be washed, dried, and finished.

Indigo is frequently applied in combination with other dyes, the objedtbeing the formation of green and other shades; the combination of theindigo-blue and chrome-yellow producing the so-called vatted green. Thisoperation requires four tanks; the contents of the first tank consist of asolution of 2 litres of subacetate of lead, of sp. gr. = 1*421, and a lime-water, made up of 2*5 kilos, of lime with water, to form a liquid of asp. gr. = 1*020 ; the second tank contains pure water; the third tank is a coldindigo vat, with 7*5 kilos, indigo ; the fourth tank contains a liquid, made upof 5 kilos, bichromate of potassa and 40 litres of vinegar. The operation ofdyeing is carried out in this manner: the goods or pieces are plunged forthree minutes in the first tank, rinsed in the second, next plunged forfive minutes in the third tank, and next rinsed in the fourth, wherein theindigo is oxidised, and simultaneously the green dye brought out. The goodsare then washed in running water, next immersed in another bichromatebath, again washed in cold water, after which the cloth is passed through acold caustic soda bath, containing for each piece a litre of caustic sodasolution at a sp. gr. of 1*070. After another wash the goods are dried andare ready for packing when they have been calendered. In this way an evenand uniform green is obtained. If an acid discharge is printed thereon, andthe goods washed, and then, if desired, immersed in a solution of bichromateof potassa and lime, the result will be the produdtion of a white pattern, oralso of a yellow on a green ground.

Another kind of green ground is produced by mordanting previously vattedcloth with acetate of alumina, and dyeing the so-prepared fabric next withquercitron, yellow berries, or weld; if instead of quercitron madder isemployed a very beautiful puce is produced. Not only the colours justmentioned, but a great many others, can be fixed on a previously-vatted andsubsequently-mordanted cloth. Goods which have been first dyed with per-oxide of manganese (manganese brown) possess the remarkable property oftaking up a far larger quantity of indigotin than they would take up if vattedwhile white ; the result is the produdtion of a black ground, whereupon it ispossible to bring out white, brown (bistre colour), and blue designs, either indischarge or resist styles. Thus there may be formed: a bistre ground,whereupon a resist having been printed gives after vatting a black ground andbistre designs ; or bistre ground, whereupon is next printed a discharge forwhite (an acid tin-salt), yielding after vatting a black ground, whereon areblue patterns; the same result is obtained when upon the black ground (thatis to say, indigo-blue after and over bistre) a bistre discharger (viz., simply aweak acid, which does not adt upon the indigo) is printed. A bistre-brownground, with resist for blue, and simultaneously a discharge for brown, yieldswhite ; this effedt is also produced by printing an acid (stronger) on the black,m which case the peroxide of manganese causes the oxidation of the indigo,*•«•, its decolouration, while the former is simultaneously decolourised,becoming converted into a soluble proto-salt of manganese. Combinations ofmdigo and hydrated oxide of iron yield similar results, but are less easilymanaged, and are not so beautiful.

What has been mentioned above concerning vat blues applies chiefly to