CHAPTER V

RETTING, BREAKING AND SCUTCHING

The retting operation is that process which converts the constituents of the stems into that condition which will enable the bast layer, see Fig. 7, to be separated easily from the remaining parts of the stem. In all fibrous plants of the type illustrated in Figs. 6 and 7, a retting process is conducted in which the plants are either submerged in water, called “water retting,” or spread on lands adjoining the cultivated areas to undergo what is termed a weathering action, or “dew retting.” Water retting is the more satisfactory and gives the better results, and, in the hands of experienced operatives a more rapid production of fibre of the better grades.

The submersion of the plants, caused by placing stones, clods or the like on to the bundles, may be in slowly-running rivers, in which case the bundles are kept intact in crates moored to the bank, or a similar submersion may be conducted in a series of tanks or ponds. In the latter case a supply of water may be allowed to enter and leave the tank, and the plants are kept there until the operation is complete. Stagnant water acts quicker on the plants than does running water.

The retting action is a process of fermentation, and the amount of active bacteria can be regulated by the temperature and rate of movement of the water. Flax retting in the river Lys, near Courtrai, is the finest system known at present, and its value is due to the slow rate of movement of soft water which is favourable to the production of the retting bacteria; the adaptation of a similar system to this where the water supply is suitable will give high-class results.

Fermentation starts soon after the plants are submerged, and the rate of fermentation depends upon the temperature of the air and water; its progress is identified by the presence of air bells on the surface of the water. As the operation proceeds, the bundles have a tendency to rise to the surface, and hence extra weights are added to keep them submerged. When the formation of air bells ceases, the operatives carefully examine and test the stems to ascertain the progress of the operation; they usually strip off part of the bast layer, see Fig. 7, from the wood or core, and their judgment of the correct stage of retting is determined by the ease with which this separation is effected. Great skill is required here, or rather ripe experience, for if the retting is not complete, a portion of the woody matter goes forward with the fibre, while if the stems are over-retted, the fibre is weak; in both cases, a faulty judgment causes trouble in the actual manual or mechanical processes which follow.

Other methods of retting are adopted in different countries, and even in certain districts of those countries where the above system is in vogue. It will be understood that the choice of any system will depend largely upon local circumstances, and in all cases, other things being equal, the method adopted will be that which will yield the largest quantity of hemp fibre at the least cost.

The characteristics of the fibres are typical of the countries in which the plants were grown, and of the processes of retting. It will be almost invariably found that the best fibre is the result of the most elaborate and careful methods of cultivation and retting, together with the equally careful and efficient subsequent processes of breaking and scutching.

It need hardly be said that the above elaborate and costly methods are adopted only for the very finest grades of fibre; they would not be attempted in the case of those plants which grow and ripen so rapidly in some tropical countries, and in which a short, harsh fibre only is obtained; for such plants the cheapest and simplest methods of extraction are practised.

Many praiseworthy attempts have been made, and others are still in progress, with varying degrees of success, to extract the fibre quickly. None has yet been able to supplant the above-described costly, lengthy and laborious process, but with modern science, machinery and experience, one might expect that some brilliant genius will ultimately solve the problem. Many industrial problems have been solved by the joint action of experience and applied science, and one might therefore hope to see a great simplification of the present hazardous operation of retting.

The successful introduction of a machine or a system of machinery which would pull, strip and clean hemp and allied plants and fibres on the field of growth would not only open up new fields of cultivation, but would increase the wealth of our country by millions of pounds; it would do much to prevent the depopulation of the rural districts and so help to preserve the hygienic conditions of our large towns.

The retting operation completed, the stems are washed and spread on grass land, if available, or stooked like grain and allowed to dry thoroughly. It is acknowledged to be advantageous to allow the stems to remain a few days on the grass, for after this exposure the fibre is more easily and efficiently separated from the other constituents of the bast layer.

The ribbon-shaped layer may be about 3 ft. long in the shorter Russian grades of hemp, but up to 15 ft. in length in the Italian grades. The colour varies from grey and brown to a rich cream and almost white in the finest grades.

The ultimate fibres are large and somewhat irregular in shape; they vary in length from 0·2 to 2 in., with an average length of about 1 in., while the diameter is only about 1/1000 or 0·001 of an inch.

BREAKING AND SCUTCHING.--Various methods are adopted to separate the bast layer from the central or woody part of the retted and dried stems of hemp, but in all cases the operation thus involved is termed “breaking.” The central woody part has to be broken into a great number of short lengths, and this is done in some districts by exceedingly simple apparatus, and in other districts by modern breaking machines. Perhaps the simplest apparatus which is used for this purpose consists of a series of Δ-shaped wooden bars arranged horizontally in the form of a grid, and into the cavities of this row of bars fits another group or series of similar bars but inverted. The latter group is hinged at one end and provided with a handle at the other.

When the handle and the upper set of bars are raised, a few hemp stems are laid across the fixed lower bars; the handle is then pressed downwards, and this causes the stems to be squeezed and broken between the two sets of bars. By repeated blows with the upper bars, and lateral movements of the stems, it is evident that the woody core would be broken, and this is done without damaging the fibrous layer. A treadle may be attached to the handle end of the hinged grid and thus leave both hands free to manipulate the stems and to remove that portion of the broken wood which has not already dropped through the slots in the lower grid but remains between the bars of the same.

The mechanical means for this purpose consist of a number of fluted rollers between which the stems pass and by the flutes of which the wood is broken. Sometimes scrapers are used in the same machine to help to remove the small particles of wood. What remains in the hand after the simple manual process is completed, or what is delivered from the machine by the delivery rollers, are the unbroken fibrous layers to which still adhere several particles of woody matter or shive as it is called. A further operation, termed “scutching,” is necessary to remove this shive and so leave the lengths of fibre as clean as possible.

SCUTCHING.--The operation of scutching may be considered in some respects in the light of a scraping action in which the broken and partially-clean, ribbon-like structures of fibres occupy a position between a fixed and a movable board, and are subjected to the friction between them. The simplest apparatus for this purpose consists of an upright wooden board with a horizontal slot near its upper end and through which the ends of the fibres are passed. The fibres hang downwards, and while thus depending a flat wooden “scutching handle” or flail--very similar in shape to a baking spit--is brought smartly with its edge to traverse downwards against the fibres, and thus to remove the objectionable shive but at the same time to prevent, as far as possible, the destruction of the fibrous layer and the accumulation of waste. The operative can expose as much of the fibrous layer as desired to the action of the scutching handle in virtue of the slot, and after one end of the “strick” is finished, the other end is treated similarly.

While the above hand method is largely practised and is quite satisfactory where comparatively small quantities have to be treated, or for very fine and expensive material where delicate treatment is essential, the modern method of scutching is done by power. The feeding and manipulation of the stricks are, however, still under the direct control of the operative. In these mechanical scutchers it is usual to employ six to twelve handles--narrower but longer than the hand flail--and these handles project from a common centre or shaft, somewhat after the form of the sails of a windmill. As the shaft rotates, the handles are brought successively to act against the fibres as in the simpler process.

Large quantities of Russian and other hemps are only partially cleaned, and are termed “siretz” hemps, while in some districts where the most valuable plants are grown, the bast layer is stripped from the stems, and the material subjected in smaller quantities to the cleaning and washing processes, thus producing a higher value fibre.

In hand scutching an operative cleans on an average about 10 to 12 lb. of Italian hemp per hour, but such quantities can be, obviously, only approximate, for the quantities prepared will vary greatly, depending as they do upon the efficiency of the apparatus at command, the degree to which the fibrous layer has to be cleaned, the quality of the material and the skill of the operator. The better grades of fibre usually and almost invariably receive more treatment than the lower grades.

The commercial value of hemp depends, as already stated, upon its strength, colour, freedom from faults, and its spinning properties; comparative values are scarcely possible unless in certain seasons, because prices fluctuate greatly according to the demand for certain grades of cordage as well as to the prices of other fibres which may be used for similar goods.

Italian hemp can be spun into thinner or finer yarns than any of the other hemps, and it is therefore a competitor with certain grades of flax. French, Chinese and Russian hemps are also valuable, and besides being used alone, are sometimes mixed with the coarser varieties of Italian hemp for certain kinds of cordage and lines.

The following table shows the amount of fibre in tons for five years in regard to Russian and Italian hemp imports to the United Kingdom.

──────────┬─────────┬─────────┬─────────┬─────────┬──────── │ 1907. │ 1908. │ 1909. │ 1910. │ 1911. ──────────┼─────────┼─────────┼─────────┼─────────┼──────── Russian │ 17,299 │ 15,753 │ 13,816 │ 12,576 │ 14,981 Italian │ 10,462 │ 8,133 │ 10,144 │ 10,298 │ 10,343 ──────────┼─────────┼─────────┼─────────┼─────────┼──────── │ 27,761 │ 23,886 │ 23,960 │ 22,874 │ 25,324 ══════════╧═════════╧═════════╧═════════╧═════════╧════════