Feathers (To Dye Blue.) The feathers must be first well washed in soap and water, then exposed to the air for several days. Lastly, after being well rinsed in pure warm water, they must be dipped in hot alum-water. A solution of indigo composition, commonly called chemic blue, having been prepared, the feathers are to be dipped therein. The immersion in alum-water, and in the dye-water, to be alternately performed till the requisite shade is obtained.