200 The Art of Byeiny. 



cochineal, not a grayish blue but a grayish brown. It is 

 necessary, therefore, to employ a protoxide salt as a mor- 

 dant. In this instance, the usual difficulty occurs, to form 

 with these mordants uniform grounds. When the calico is 

 impregnated with a mordant consisting of 10 lbs. sulphate of 

 iron, 40 lbs. vinegar, 40 lbs. water, and 10 lbs. sugar of lead ; 

 allowed to dry in heated air ; washed with water equally 

 after the drying, and dyed with cochineal, a very clear 

 grayish blue is obtained, but highly unequal and full of 

 spots. So soon as the calico becomes dry, before the dye- 

 ing, a quantity of clear matter appears grouped together, 

 produced by the action of the oxygen of the air, in conse- 

 quence of which, the mordant is spread irregularly over 

 the calico. This may also be observed after the dyeing is 

 completed. 



It is best to produce this colour with the pyrolignate of 

 iron. The matter which it contains prevents its rapid 

 change in the air, so that it remains equally absorbed by 

 the calico. Pyrolignate of iron is also thicker ; hence, this 

 will be an obstacle to its flowing. It is important that the 

 calico should be rapidly dried and dyed equally afterwards, 

 without allowing it to hang long. The same occurs in 

 printing as the thickening prevents the action of the air. 

 The calico, in this case, is purified by rinsing in running 

 water. A hot cow-dung bath acts, in this instance, very 

 injuriously. 



To form a dark blueish gray, 7 lbs. of mordanted cloth are 

 used for 1 lb. of cochineal. The cochineal should be suf- 

 ficiently pulverized by passing it through a coffee mill. 



If the cochineal powder is introduced into a lukewarm 

 solution, and the cloth placed in it, many dark spots are 

 formed. The cochineal should, therefore, be boiled strongly 

 with a little water, and this decoction added to the vat. 

 The water should be very pure ; especially it should be 

 free from lime. This colour does not improve either by 

 soap or other means. 



Properties of cochineal hlue-yray. This colour withstands 

 the action of light and air longer than the cochineal red. 

 Therefore, in this respect, it cannot be termed a fleeting 

 colour. But in soap- suds it is completely changed. When 

 a piece of calico, dyed of a dark shade, is boiled for a 



