DYEING. 189 



It is not possible to give to cloth a permanent 

 yellow colour without the use of mordants. Alum 

 is the most usual mordant. Wool is dyed yellow 

 by weld, by the use of alum and tartar. Quercitron 

 bark gives nearly the same colour, but more abun- 

 dantly, and it is rather cheaper than weld. The 

 process is as follows : boil the cloth for an hour or 

 more in a solution of alum, and then immerse it in 

 a bath of quercitron bark. Next add a small quan- 

 tity of clean powdered chalk, and continue the 

 boiling for eight or ten minutes. The yellow thus 

 given will be as good as that obtained from weld. 



If very bright yellows are required, the tin mor- 

 dant must be used ; and sometimes alum is added 

 to the tin. 



If an addition of tartar be made to the mordant, 

 the yellow will have a slight tinge of green. 



If an orange or an aurora be required, a small 

 portion of cochineal must be added. 



Silk used formerly to be always dyed yellow 

 with weld, but quercitron bark is now found to 

 answer equally well, and at less expense. The 

 proportion should be from one to two parts of bark 

 to twelve pounds of silk, according to the particular 

 shade of colour wanted. The bark, powdered and 

 tied up in a bag, should be put into the dyeing 

 vessel whilst the water is cold, and as soon as it 

 becomes blood warm, the silk previously alumed 

 should also be put in and dyed as usual, and when 

 the shade is required to be deep, a little chalk or 

 pearl-ashes may be added towards the end of the 

 operation. 



When very lively yellows are required, a little of 

 the murio-sulphate of tin may be employed as a 

 mordant in addition to the alum. Annotto com- 



