The greater part of the tissue, and the whole of the gum, mucilage, and bitter principle, having been removed by the stripping and washing processes, the next step is to destroy the green colour in those parts of the tissue still adhering to the fibre. This is effected by the operation of bleaching. If the fibre, on leaving the water, be dried at once, without exposure to the sun, it will dry green ; this colour will survive for a long while, but can be removed at any time, by simple wetting and exposure to the sun. Usually, the operation is performed at once. In summer, the fibre is spread thinly on clean grass for 4-5 days, then turned over, and left for 2-3 days longer ; when dry, it is taken into store. In winter, it is left on the grass for 2-3 weeks, and is then finished by hanging on wires or poles, exposed to sun, wind, and rain. After about 5 weeks' exposure, it begins to lose strength, and, if badly dressed, will commence to deteriorate much earlier. Each row of wires should consist of 3, arranged in a triangle, so as to keep the fibre open, and admit the air. The rows should be 10-12 ft. apart, so as to admit oarte. About 1 ton of fibre will occupy 1 mile of wires, so that in winter a mill would require miles of them, covering 2-2i acres of ground. About 15 acres of bleaching ground would also be necessary for a mill running 3-4 machines ; and storage room for 15-20 tons, or about 12,000 cub. ft.
The next operation is scutching, which is intended to straighten out and clean the fibre thoroughly from the pieces of dry tissue still remaining on it, and from the dust and dirt picked up during the drying and bleaching. Scutching has been described at length when speaking of flax (Linum usitatissimum)—see p. 973 ; but the great length of the phormium fibre makes it much more difficult to scotch than flax. The process would be facilitated by cutting the hanks in two, so as to have lengths of 4-5 ft. A perfect scutching-machine has yet to be invented. The loss of fibre in scutching commonly amounts to 3-5 cwt. a ton.
The difficulty of effectually cleansing the fibre by purely mechanical means—beating and washing in water—has led to experiments in other directions. The principal methods which have assumed a practical form are the following :— McMillan's : three distinct ways are adopted for removing the extractive matters—(l) Boiling with cow-dung for 2-3 hours, and then washing in cold water ; (2) boiling with small proportion of common salt for 1 hour, and washing ; (3) boiling in sea-water for 1 hour, and washing. The fibre is of equal quality from each process, but is of better colour in (2) and (3) than in (1).
Journeaux's: the crushed leaves are softened by a water-bath at 88° (190° F); then passed between pressure-rollers to remove refuse matter ; then subjected to vinous fermentation in a water bath at 32° (90° F.) : finally squeezed, washed, and dried.
Thorne's : the leaves are crushed, and washed in cold water ; then subjected to a bath of boiling water, in which animal matter has been digested.
Nattrass's : the leaves are boiled in a solution of prussiate of potash, before the fibre is extracted.
A more generally useful improvement is the application of a small quantity of oil to the fibre, adding to its appearance, and reducing its liability to undergo further maceration in water. The best time to apply the oil is at the end of the scutching ; the fibres might be lightly coated with oil while passing through a second scutcher for the purpose. Animal oils may be used, but a propor tion of mineral oil would perhaps be better. Fibre intended for export should not be oiled. Tarring is not advisable.
Baling .—A uniform size of bale similar to that of Manilla (Musa textilis)-3 ft. 3 in., by 1 ft. 8 in., by 1 ft. 8 in., is most suitable. The bales should be well covered, and not bound with iron lashings.
Characters and Uses of the Fibre.—A section of the leaf of the phormium plant, taken in the thin part, is shown in Fig. 699: e, epidermis ; p, coarse parenchyma ; p', parenchyma filled with grains of chlorophyl ; f, fibro-vascular bundles, coloured very slightly yellow by test H; mag. 100.
The fibres are nearly white, soft, supple, and of silky lustre ; the bundles axe of irregular size, separate with difficulty, and are very elastic and light. Their breaking strain, when the force is gradually applied, is high, viz.
as compared with flax and hemp 161 ; but they break readily when bent or knotted.
The isolated fibres are of regu lar diameter, their walls have a uniform thickness, and the surface is smooth. They are stiff, straight, and very fine ; the central channel is very evident. The ends taper regu larly and gradually, like those of flax. The fibres are repre sented in Fig. 700: a, sections of groups of fibres ; b, fibres seen longitudinally ; e, ends ; mag. 300. The fibres are coloured distinctly yellow by test F. Their dimensions are : —length: max. 0.59 in. ; rain., 0.196 in. ; mean, 0.354 in. ; diameter : max., 0.0008 in. ; min., in. ; mean, in. A comparison of the fibres of Phormium tenax, Musa textilis (Manilla hemp), and Agave sisalana (Sisal hemp), shows the mean length of their ultimate fibres to be respectively 0.39 ih., 0.21 in., and 0.21 in. ; the mean diameter of the ultimate fibres to be 0.00045 in., in., and in., and the thickness of the cell-wall, in., in., and in. Samples of phormium fibre exposed for 2 hours to steam at 2 etmos., then boiled for 3 hours, and again steamed for 4 bouts, lost 6'14 per cent. by weight, against Manilla hemp, 6'07 per cent., and hemp, 6 •44 per cent.