Bamboo and Rattan/Rattan/Course-2 Unit-1
Up to10% of the mature growing stock of rattans can be harvested at a rotation of three years from clumps of age 6 to 15 years. The older the better in respect of number of stems and also length in each clump. A single clump may yield about a a quintal of canes of about 15 years of age. Care should be taken to harvest only the mature stems which exhibit loosening of leaf sheath and exposure of lowest part of the stem. It is suggested to limit the harvesting only in the dry season. Unwinding the canes manually from the branches of supporting trees instead of pulling them to avoid breaking and wastage of the top portions.
Harvesting responsibility remains with the Forest Department. Annual lessees, or harvest permits are issued to local societies of the rural folk, socially and economically backward communities, registered contractors, etc and they harvest the canes in close observation by the Forest Department field staff. Piece work rates (rate per bundle) or labour charges are fixed for bringing bundles of a fixed number of canes (usually 20) to appointed Forest Depots.
A selective felling system is adopted for the extraction of canes with the following rules:
i. Only mature canes should be removed from the clumps while immature or tender canes should not be collected or damaged.
ii. Digging of rhizome or roots will not be permitted.
iii. No canes shall be extracted from outside the specified blocks.
iv. All the one-year-old culms and six culms of the second year shall be retained in the clump.
v. Clumps consisting less than six culms shall not be worked.
vi. Felling should be done at not less than 15 cm and not more than 30 cm from the ground level.
Under the present system, the stem is cut below the level of 30 cm height from the ground using a chopper and dislodged from the canopy by dragging. When it is difficult to drag the entire stem in case of relatively tall rattans, cutters have the tendency to cut the stem at reachable height, which is often less than half the length of the stem and leave the upper portion in the canopy as a waste. Harvesting the tall stem is very laborious and 5-6 labourers find it hard to drag the stem of 15 m length or more in the thick canopy. In undisturbed areas, the canes of 25-50 m length are not uncommon. Thorny leaf sheath is another problem as it often causes physical injuries in working.
Soon after felling, mostly thick (large diameter) canes are cut into 12 feet (3-4 m) lngth and small diameter ones into 15-16 feet (4-6 m) in the felling site. Bundles of 20 pieces ae made to conveniently carry to an intermediate site, which is generally 2-5 km away from the felling site, and stacked besides the road for truck transport. When the extraction is in small-scale operation, instead of trucks, workers are engaged for head load transport by foot up to a distance of 10-15 km or more.
Generally, the rattans are unloaded from the trucks in a convenient intermediate site for sorting and drying before delivery to the manufacturing units. Rattan extraction is mostly carried out during relatively dry season between December and May in order to prevent excessive fungal degradation. At present no preliminary processing (including on-site preservative treatment) method is in practice before conversion although recently many such systems (on-site prophylactic treatment, oil curing, grading, etc) were developed and suggested.
i. Oil curing
Immersing the large diameter canes in hot oil/oil mixtures (using specially designed curing tub) for specified duration just below the boiling point and subsequent cleaning and drying yield an ivory white colour and better appearance. While the moisture content got rapidly down due to curing, additional benefit of better control over subsequent fungal attack is another plus that can be achieved due to oil curing. Use of the optimized curing conditions ensures no adverse effect on the physical and mechanical properties of he cured rattans so that the utilization value is affected (see the section on oil curing for further details). Oil cured canes have great domestic as well as export demand and is fetching more price. Hence, adoption of this value-addition technique will impart better color, control over further fungal attack and resulting better marketability and prices.
Fig. 1. Gradual color change of canes from green to ivory white during sun drying for a week after curing
(in contrast to untreated canes, in the left side).
How to oil cure rattans?
Although, oil curing technique is practiced in the rattan rich South-East Asian countries the code of practices varies widely among the different industries and countries depending on their traditional belief. As many as eleven types of oil mixtures are reported from Indonesia; components of which consists of Diesel oil, coconut oil, kerosene, water, chemicals like sodium nitrite and sulphur in different proportions, no clear distinction of the effects of different combinations on the quality of canes has been established. As there is no scientific information on the effects of these practices on utilization value, no standards are available with regard to the composition of oil mixtures or duration of the curing treatment. Thus the existing practices are quite diverse in the field of cane product manufacture. It was in this context, Dhamodaran and Bhat (2002) standardized the oil curing technology and according to this study, a 9:1 ratio by volume of diesel and coconut oil or kerosene alone with a curing temperature below the boiling condition of the oil medium was identified as the best curing condition.
Curing duration of 20 minutes for small diameter, 30 minutes for medium and 45 minutes for large diameter rattans were found to be effective in imparting the desired ivory white color to rattan skin without affecting their physical and mechanical properties. However, curing periods of shorter or longer duration as against the prescribed ones were found to have adverse effect on the properties of the treated canes. As high temperature causes damage to rattans in terms of shrinkage and charring and also increases the risk of fire hazards, temperature needs to be maintained strictly below the boiling point of the oil medium.
It was found that curing has the desired effect on the skin color, only if it has been applied in the green canes, immediately after harvesting. Inadvertent delay in treating after harvesting causes infection by fungal organisms (due to the high moisture content) leading to sap stain which affects aesthetic value of the material. Once the stain marks have appeared, these cannot be removed by curing later. Also, curing the canes immediately after harvesting can reduce the moisture content rapidly to almost the level of air-dried material. As the traditional processing methods take several weeks to bring down the moisture content to this level, the chances of getting infected by fungi are high. This also necessitates that curing to be carried out as early as possible in the field itself. Hence, the curing unit needs to be established in a place or collection depot, near the harvesting region. More than few days lag between harvesting, transportation and curing is not desirable.
Oil Curing Facility/Equipment
For the application of the cane curing technique, the primary requirement is a curing tub of appropriate dimensions (2.4 m - 3.6 m or 4.8 m long, width 0.75 m, height 0.75 m; made of mild steel of 2-4 mm thickness) (Fig. 2 & 3). For heating the oil mixture, source of heat can be firewood, kerosene or LPG depending on the convenience and accordingly the design of the heating system varies. Use of fire wood requires a mud hearth and chimney (Fig. 4 & 5) while use of kerosene or LPG requires stove type burners (Fig. 6 & 7). Use of LPG as fuel is also convenient and effective for controlled heating, as longitudinal burners are available for use with gas (Fig. 8). This will ensure more uniform distribution of heat within the oil medium. As localized heating can be avoided by the use of longitudinal burners, the chances of fire hazards can be effectively controlled. Moreover, in the case of emergency, the entire supply of LPG can be cut off by the use of a single control valve. Fire safety measure is a crucial aspect in the modified curing system. Direct exposure of hot oil vapor to the flame and chances of any fire hazard are minimized by concealing the burners within a metallic bracket (Fig. 9). A dial type thermometer (Fig. 10) is attached to the curing tub to indicate the appropriate levels of temperature.
Fig.2. Drawing of the oil curing tub. Fig. 3. The newly designed tub for curing the canes
Fig. 4. The mud hearth and curing system designed for the use of firewood as heat source.
Fig. 5. An illustration of the mud hearth design - Longitudinal sectional view
Fig. 6. Curing tug system designed for the use of kerosene as heat source Fig. 7. Newly designed tub for using LPG as heat source.
Fig. 8. Gas pipes and longitudinal burner concealed within brackets. Fig. 9. Metallic bracket used for concealing the burners.
Fig. 10. Dial type thermometer. Fig. 11. Cane curing system with metallic chains for lifting the bundles.
Fig. 12. Raised wooden/Bamboo platform near the cane curing unit for rubbing the oil-cured canes with coir or gunny cloth.
Fig. 13. Some traditional tools usedin cane processing.
How to Cure Canes
About half of the tub is filled with the chosen oil mixture (Kerosene alone or Diesel and coconut oil in the ratio 9:1 by volume. The tub is carefully and slowly heated to raise the temperature up to the boiling condition and then the temperature maintained at that level. In each batch, 2-5 bundles of 20 canes of full length (12-16 feet) can be cured. Keep the bundles immersed in the oil by using some weights above the bundles for the desired duration (20, 30 and 45 minutes for small, medium and large diameter canes respectively) and stir occasionally by using some wooden sticks. Utmost care has to be taken in controlling the temperature and managing the flame so as to avoid any fire hazard. Maintenance of uniform temperature below the boiling condition has the advantages of moderate shrinkage of cured material and prevention of fire hazard while moisture gets evaporated from canes.
After curing the canes in the hot oil for the required duration, the bundles are lifted with the help of metallic chains provided (see Fig. 11) and placed either over the wooden poles placed across the tub or over the tightened chains to drain the excess oil to the tub itself. Gentle shaking of bundles using wooden sticks/hooks will hasten the draining process. The oil-cured canes are removed from the tub and are transferred to an elevated wooden platform (made with bamboo poles) for rubbing with coir or waste gunny cloth (see Fig. 12). This process removes most of the mucilaginous or waxy substances and to some extent the silica deposits from the surface of the stems. The subsequent rubbing with dry gunny cloth imparts polish and improves the glossiness of the stem. The cured canes are then to be straightened by bending in opposite directions with the help of a wooden gig and end-trimmed by a specially designed scissors (Fig. 13). The scissors should be sharp enough to give a clean cut to avoid end splitting. The polished canes are spread out in the open area and sun-dried for a week. Gradually the skin color changes from green (or often straw color) to an ivory white (Fig. 1). While drying, it is essential to cover the canes with polythene sheets or plaited coconut leaves during nights to prevent dew deposits and subsequent fungal infection and staining.
The trimmed straight canes are tied into tight bundles of 100 pieces, neatly stacked and covered with polythene sheets/plaited coconut leaves for further transport to godowns and marketing. Generally, canes will be supplied to manufacturing units from such godowns. It is also found that the additional investment on curing is very marginal (in the tune of 29% of the original value during 2002 and in the context of improved quality and ready acceptance by the cane furniture manufacturers, this is well justified. International markets demand rattans of ivory white-to clear straw color which fetches more price. Oil cured canes add value to furniture and traditional house-boats in the eco-tourism industry. Thus adoption of oil curing technique for better aesthetic appearance and enhanced durability of the products can be a footstep for achieving sustainable development of rattan sector by efficient and value-added utilization of the available resources.
Fig. 14. Oil-curing adds value to the furniture, handicraft products and traditional houseboats in eco-tourism industry.
ii. On-site Prophylactic Treatment
An effective on-site prophylactic treatment for freshly cut green canes is suggested for preventing immediate fungal infestation (Mohanan 2002). Fungal staining and deterioration can be minimized by giving protective chemical treatment immediately after extraction. As the invasion and growth of the fungi occur within 24 hours of extraction, prophylactic treatment should be given immediately after the extraction to obtain stain and blemish-free material. Although, signs and symptoms of fungal staining do not appear immediately after the invasion of the fungi, fungal hyphae invade the cut end tissues. If staining fungi are not controlled at this stage, these will continue to grow within the internal cortical tissues at a very high rate and symptoms become evident on the fifth day onwards after exposure.
The freshly harvested rattan poles should be immediately transported from the felling sites to the processing units for giving protective measures. However, this is not practicable due to the fact that it takes two to three weeks or even a month to reach the processing units. By this time, most of the rattan poles might have been severely infected and discoloured. Hence, it is more practical and desirable to give the prophylactic treatment to freshly harvested rattan poles at the harvesting sites itself.
Remove the leaf sheaths from the freshly cut rattan and cut into desired length. Stack the poles vertically and allow the sap to drip off through the cut ends for at least half an hour. Prepare an aqueous solution of 4% copper sulphate or 1% sodium pentachloro phenate (Na PCP) or 0.05% a.i. Busan 30. Soak the poles in bundles (of 20 poles) in the preservative solution for about 10 minutes.
The soak treatment can be done in a dipping vat made of GI sheet, or a dipping pit dug on the ground and lined with polythene sheet (Fig. 15). A pit of 4.5 m long, 1 m wide and 0.6 m deep will serve the purpose. The edge of the polythene lining sheet should be about 30 cm above the soil surface so that the solution will not spill into the pit or ground. Place some soil on the edges and press the edges of the plastic sheet tightly against the soil surface. Fill the tank with known volume of water, add calculated quantity of the chemical to get the desired concentration and mix thoroughly with a stick. Place two plastic ropes across the tank to facilitate putting the rattan poles into the treatment tank as well as taking out the treated poles.
The cost of treatment per large diameter rattan pole of about 4 feet length is estimated to be about Rs. 0.20 only.
Fig. 15. Treatment pit dug on the ground and lined with polythene sheet