The feathers are put into a bath of permanganate of potash, containing 4 to 5 parts permanganate to 1000 of water; a solution of sulphate of magnesia of the same strength is added, and it is heated 140 ° F. (60 ° C.) at the most. The feathers previously washed, are put into this bath, then taken out, rinsed, and passed through Weak sulphuric acid at about 1½ ° to 3 ° Tw.
It is also possible to bleach the feathers in a bath of 1 part barium peroxide in 100 of water at 86 ° F. (30 ° C.). Leave 48 hours in this solution, wash, pass through weak acid bath, and wash.
Feathers may be bleached by exposure to the vapour of burning sulphur (sulphurous acid) in a moist atmosphere, but it is usually necessary to remove the oily matters from them before they can be satisfactorily so bleached. This may be accomplished by immersing them for a short time in naphtha or benzine, rinsing in a second vessel of the same, and thoroughly drying by exposure to the air. This treatment does not injure the feathers.
Peroxide of hydrogen is largely employed. The advantage it offers is the oxidation and complete disappearance of the colour, without spoiling the structure of the feather. The feathers are first dipped in a solution of 1 to 2 per cent, carbonate of ammonia in water, in which they are slightly agitated, and left for about 12 hours at 68 ° F. (20 ° C.). The feathers are then taken through a tepid white soap bath, and well washed in water which is free of lime. The treatment with benzine and ether also gives good results. The bleaching bath is neutralised. Wood or metal vessels are not recommended for the baths, and it is better to use earthenware vessels. When bleached, the feathers are dried slowly at a low temperature in a draught, and are often beaten. A good result is obtained by dipping the bleached feathers in alcohol, which gives them a finer appearance. The succeeding operations are the same as by other processes. This method of bleaching feathers is said to prove superior to all others. Black spots are perfectly bleached after being exposed for some time.
The feathers are placed for 3 to 4 hours in a tepid dilute solution of bichromate of potash, to which some nitric acid has been cautiously added. After this lapse of time, the feathers will have assumed a greenish j hue, owing to the chromium oxide precipitated; to remove this, they are placed in a dilute solution of sulphurous acid in water, when they become perfectly white. Care must be taken that the bichromate bath is not too strong, and especially that excess of nitric acid be avoided.
The objection attending the use of acid or alkaline baths is that they alter the texture of certain feathers. In Roy's process, the feathers are first soaped, and, after thorough washing, subjected to the action of ozone. By a succession of immersions in water and treatments with the gas, bleaching is effected without injury to the feathers.
Viol et Duplot's method rests on the fact that the feathers immersed in resinous essences (e. g. turpentines, oils of lavender, thyme, etc.) or bituminous hydrocarbons, are bleached under the influence of light or heat. The feathers are kept in the vessels a longer or shorter time, according to degree of whiteness desired (generally about 3 or 4 weeks), at a temperature of 86 ° F. (30 ° C.), and exposed to the light.
The common method is as follows. The feathers are first washed in soap lather, well rubbed with the hands, and passed through clean scalding water. For white feathers, they are first exposed to the action of sun and dew for about a fortnight, washed in a hot bath containing Spanish white (the softest and purest white chalk), and passed through 3 clean waters; next they are blued by a rapid passage through a cold bath containing indigo; after this, they are sulphured by suspension in a sulphuring stove; and are finally hung upon cords to dry, being occasionally shaken to open the fibres.
Scouring and bleaching are two distinct operations, the former tending to remove from the material all fatty substances, while the latter consists in rendering the feathers perfectly white, after having been cleansed from their fatty contents. According to quality, the first washing in soap is done at 100 ° to 122 °F., the bath to be prepared in the proportion of 500 parts by weight of white Marseilles soap for 600 of water, and well beaten up into a lather. Lay down the feathers and rub them well by hand until the bath is exhausted and has lost its detergent power. Then let it out, and repeat the operation with a fresh bath of the same composition; then remove the soap by rinsing in 2 or 3 waters at 100 ° F. Prepare a cold bath of 45 to 62 gr. of bioxalate of potash to 5 qt. of water, lay down the feathers for 15 or 20 minutes, lift and rinse in cold water. After passing them 3 or 4 times through the cold water, the feathers are to be blued. For this purpose add to a fresh bath of cold water so much solution of (methyl) aniline violet as will give the water a faint tint; open the feathers well and agitate them in the bath until they also have assumed the tint; then squeeze them out in a clean white piece of cloth (muslin), and pass through a pretty thick solution of raw starch (8 oz. to 4 qt. water unboiled), squeeze out again, open them by passing the hand lightly over the stem, and dry either in a warm place, or preferably in the air, shaking them repeatedly while drying in order to perfectly open the fibres. Finally beat out the remaining starch either by hand or by means of a soft brush.
The peroxide of hydrogen process is undoubtedly better than using sulphurous acid, for though it costs more, it is less likely to injure the feathers if unskilfully done. For the peroxide, first soak the goods for a few hours in a solution of 3 oz. of carbonate of ammonia to 1 gal. of water, then wash in warm soap and water, using Castile or white curd soap. Pass through clean soft water, and they are ready for the peroxide bath. Make a solution of 1 part hydrogen peroxide to 10 of water, and immerse the feathers in this. Take out, wash in clean water, dry slowly and curl. To get a pure white the feathers may go through a warm soap bath having a little blue powder in it. Dyeing may be done as soon as the bleaching is completed. Dyeing dark colours is done without bleaching, the feathers only being softened with the carbonate of ammonia and washing.