The whole secret of feather dyeing lies in the proper attainment of these three requirements, success in which depends respectively upon (a) the composition of the dye-bath, (b) the method of dyeing, and (c) the finishing process. =(a) The Dye-bath.=—As is universally the case when using Acid dyes on animal fibres, the bath must be distinctly acid, in order to release the free color acid from the dyestuff, which, in its commercial form, is a salt. A very little experimenting with ostrich feathers will show that the presence, not only of mineral acids like sulphuric or hydrochloric, but even of the much milder organic acids, like acetic or citric, is liable to “burn” the feather badly and convert a well barbuled flue into a bare fibre which, under no conditions, can look other than stringy. The acid commonly used by the professionals is oxalic acid, but, of late years, dyeing chemists have been introducing into the dyeing industry the use of the volatile and pungent formic acid, and in the dyeing of ostrich feathers this acid has been found particularly advantageous. Excepting when a large number of feathers, strung together on a line, are to be dyed the same color, it is customary to dye feathers in an agateware pan or flat dish, and about two-thirds of a teaspoonful of formic or oxalic acid in a pint of water, is about the right proportion for one or two feathers at a time. =(b) Method of Dyeing.=— _Softening the Feathers._—Before immersing the feathers in the dye-bath the greatest pains should be taken, first, to thoroughly cleanse them, and, second, to thoroughly soften them. As a rule, the feathers are bleached before dyeing and in this process they generally lose all of their original grease. But if they show signs of wetting unevenly when plunged into hot water, they should be carefully scrubbed with Castile soap and hot water, and well rinsed till the last trace of soap has been removed. The clean feathers should then be thoroughly softened by immersing them in hot water. This is especially important as regards the quills and the stems, which may have to soak for half an hour or more before they are soft enough to take the dyestuff. _Dyeing the Feathers._—After softening, each feather is held by the tip, and laid, butt first, in the dye-bath. For light shades the dye-liquor may remain cold, but for darker shades it is best to enter the feathers at a low temperature, and raise the latter very gently till the right shade is reached, or the bath is decidedly hot, although still far below the boiling point. Above all, care must be taken to dye the quill and butt first, and to keep them in the bath very much longer than the flues and tip. The latter will dye in a minute or two, but to thoroughly stain the former may take twenty minutes or half an hour.