Walter Liese is Professor Emeritus
of the Institute for Wood Biology,
University of Hamburg, Hamburg, Germany.
In addition to processing innovations, increased knowledge of structural characteristics and species differences can help enhance future utilization of rattan.
Processing is a key issue for fur-ther development and utilization of rattan. Rattan processing is done at various levels of competence and intensity: as a cottage enterprise, in small and medium-sized factories and by larger companies.
Air seasoning of rattan stems in Kalimantan, Indonesia
- W. LIESE
Post-harvest treatments - including drying (seasoning), oil curing, bleaching, deglazing to remove the silicified epidermis and fumigation - are necessary to avoid defects and to increase processing possibilities and market value. The cane quality and the product's value on the local and international markets determine the choice of processing methods.
This article summarizes the progress achieved during the past 20 years and highlights existing gaps and constraints. It includes some observations from laboratory work on structural characteristics of rattan as a material, which may influence future utilization of rattan and the choice of species for commercial processing.
Curing of rattan bundles in a hot oil bath to reduce moisture content, Malaysia - W. LIESE |
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Proper drying of canes is necessary to maintain the high quality of rattan products. The moisture content of fresh stems varies between 130 and 160 percent, with an increase from the base upwards.
Seasoning has to start in the forest. Traditionally, bundles of 20 to 30 cane pieces are kept in erect position against a tree for about a week to drain off the sap and water. The poles are then spread out on the ground in an open yard before delivery to the processing site, where they are placed in a wigwam formation for about two to three weeks so that the moisture content is reduced further to less than 20 percent. During the drying process curved parts can be straightened by placing weights over horizontally stacked poles.
Simple grading of rattan takes place at the level of local village processors - W. LIESE |
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Harvesting and drying should preferably be done during the dry months to reduce the initial moisture and to speed up air seasoning.
Curing is the immersion of canes in a hot oil bath to prevent deterioration by reducing the moisture content (Bhat and Dhamodran, 1993; Silitonga, 1989). It is often an integral part of the processing line.
The stems, as fresh as possible, cut to the desired length and bundled, are soaked for a given time in an oil bath. The oil penetrates the cane axially, while radial penetration through the skin is almost nil because of its refractory anatomical structure.
Many investigations have been carried out to determine the best methods for curing. Different combinations of diesel oil, kerosene, palm oil and coconut oil are used, depending on availability, and are applied at varying temperatures between 80 and 150ºC for 10 to 60 minutes; the duration depends on the cane diameter. Differences among species in their responses to treatment have apparently not been established. In general, a treatment with kerosene oil at 100 to 105ºC for 20 to 45 minutes (depending on the stem diameter) appears to be best for improvement of skin colour.
After curing, the stems are drained of excess oil and rubbed with sawdust, coir (coconut husk fibre) or rags to remove the waxy substances and silica deposits on the skin. During the subsequent sun drying, often in a wigwam-like formation, the colour changes from green to ivory-white, the most desirable colour for rattan. After one to three weeks, depending on species and weather conditions, the canes are stored under cover.
In some rattans, especially some Calamus species, the outer part of the rattan stem, the epidermis, is heavily encrusted with amorphous silica which hinders processing. In highly silicated species the silica layer must be flaked away (deglazed). This is done by bending the stem, repeating the operation at intervals all along its length.
Cleaning of a rattan stem in Malaysia - W. LIESE |
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The grading of rattan stems is a very important, although still controversial, step in processing. Grading is crucial to trade and influences producers, processors, exporters and importers, as well as the end users.
The first stage of grading is carried out at the level of local village processors or, on a larger scale, intermediaries or trade centres. The criteria at this stage are dimensions (thickness, length of cane and internodes), hardness and defects. Canes are frequently divided into categories of large and small diameter; 18 mm is the most widely used cutoff. Hardness (related to anatomical characters, differences among species or age of stems) is tested by bending the stem by hand and noting whether it regains its original form quickly or slowly, or breaks. A second stage of grading, mainly aesthetic, is done on the basis of surface colour after processing.
Grading rules and procedures differ widely from country to country. In most producing countries the rattan grading rules are not precisely formulated. They often present confusing terminology and non-standardized grading practices, and consequently allow the production of substandard rattan goods. A certain simplification and unification among countries is necessary for internal and external trade (Bhat, 1996). On the basis of an extended survey, Bhat (1996) proposed model rattan grading rules with a standardized terminology (containing 20 terms), definition of defects (nine terms), methods for clarification, nomenclature of commercial rattan species and grading rules for large- and small-diameter canes and split rattan. The application of general grading rules would benefit trade, assist market standardization and help reduce material wastage.
At the village level, stems are bent and shaped after they are softened by heating with a blowtorch, as shown here in Kalimantan, Indonesia
- W. LIESE
Secondary processing involves peeling, splitting, steaming, bending, dyeing, sanding and finishing. Peeling (removal of the outer layers to obtain the inner core) and splitting are often done by hand with traditional knives or by using simple machines.
Rattan structure can be used to distinguish species suitable for utilization (e.g. a Calamus species, A) from less promising species (e.g. a Plectocomia species, B)
- G. WEINER, W. LIESE
At processing plants, steam chambers are used to soften the stems so that they can be bent; if the rattan is not steamed (because steam facilities are lacking, for example), bending can cause damage to the cane. At the village level, a blowtorch is frequently used to soften the stems for bending and shaping. Sanding and scraping are then required to remove, at least partly, the burn marks left by the blowtorch.
Several measures can be applied to improve surface appearance, which is the main criterion for marketing. Grey-brown canes can be bleached with hydrogen peroxide or other chemicals for a better finish. Discoloured canes (see Box) are often coloured artificially with a wide range of colours; the outer stem layer takes up the colouring liquid quite well. Melamine coating is used for a smooth finish. Fumigation with sulphur dioxide not only sterilizes the canes, but also improves surface quality.
Defects caused by staining and insect attack Because of its high starch content, rattan is particularly liable to infestation by fungi and insects. Defects resulting from infections by staining fungi and beetle attack can result in severe losses. Fungi cause discoloration of the canes, while beetles cause pinholes or worm holes. Furniture made from blue-stained poles painted black to hide the defect, Kalimantan, Indonesia - W. LIESE
The most common cause of staining is blue stain fungi which penetrate with their hyphae deep inside the stem, utilizing starch and sugar. It is estimated that about 20 percent of harvested canes become stained. Fungal invasion can occur within one day of cutting. Staining can be controlled by spraying or soaking in preservative solution, but prophylactic treatment is seldom applied within 24 hours as required because of difficulties posed by harvesting procedures, storage and transport. In addition, the danger of environmental pollution and regulations against the use of chemicals, where these exist, restrict the application of chemical preservatives. Canes arriving at the processing site for air seasoning are often already infested. Stained canes are often coloured to hide the defect. Through intensive marketing, furniture in various colours has become fashionable. However, heavily stained material cannot be used for furniture since its bending strength is reduced; it is often utilized for baskets and other perishable products, or even as fuel. Poles can also be discoloured by surface moulds if transported or stored under humid conditions. Unlike blue stain, this discoloration is only superficial and can be wiped off. Nevertheless, the surface shine is reduced (Kumar, 1993; Mohanan, 1993). At moisture levels of more than 20 percent, decay fungi can also attack the stem. Such infections are often noticed only at a later stage, when the fruit bodies appear, and they can cause serious structural degradation of rattan in service. Seasoned poles with a moisture content of 50 to 100 percent are liable to insect attack, mostly by the powder-post beetle. The beetles deposit their eggs in the large pores at the cross ends and the larvae are nourished from the starch content. The presence of light-yellowish powder beneath the poles is an indication of an ongoing infestation. Infested material has to be sterilized or burnt. For protection against beetles an insecticide has to be applied very early, usually by dipping or soaking. Again the consequences of pollution must be taken into consideration. The availability and legal acceptance of suitable preservatives differ from country to country. Goods for export can be sterilized in containers at the harbour by an approved agency. If slightly infested material is discovered at debarkation, the choice between fumigation and disposal by burning is at the discretion of the authorities and the buyer. |
Because different rattan species vary significantly in structural and aesthetic properties, the relatively small number of rattan species used is a major limitation. Globally, only about 50 of the 600 known species are utilized commercially; in the Philippines, 12 of 68 belong to this category (Tesoro, 1988). Rao, Ramanatha Rao and Williams (1998) have prepared a priority list of 21 Calamus species using as criteria cane size, commercial potential, quantities available and properties for processing and utilization.
The silica content varies considerably among species (0.9 to 2.7 percent). For specific products such as ropes and binds, species with low silica content should be selected.
Skin colour is an important criterion. Calamus caesius is desirable for high-value products because of its yellowish-cream colour with good lustre. The anatomical base for such an appearance is still unknown.
The processing and utilization of rattans are influenced to a great extent by the structural composition of the stem, which exhibits considerable variation along the stem length. Unlike those of softwoods and hardwoods, the fibres in rattans are still alive, and the fibre walls thicken with age. Accordingly, from the basal to the top internodes, and also from the periphery to the centre of a given internode, the fibre percentage and fibre cell wall thickness decrease, whereas the vessel diameter increases. As a result, the lower stem parts have higher density (and thus strength), whereas the upper parts exhibit higher moisture content and higher volumetric shrinkage. Thus shrinkage and warping tend to be problems when prematurely harvested stems or the upper parts of the stem are used.
The anatomical characteristics of fibre content, cell wall thickness and vessel diameter also vary among species and appear to determine the stiffness and breaking behaviour of rattan both within a stem and among the species (Bhat, Liese and Schmitt, 1990). If the top portion of a stem is integrated as a furniture component, it may break more easily because of its smaller fibre walls. Similarly, certain species with low fibre content, thinner-walled fibres and relatively wide xylem vessels, e.g. Calamus metzianus, break easily.
The differences in stem composition among the 13 rattan genera, and even among some species of one genus, have made it possible to develop an identification key for 284 species investigated (Weiner and Liese, 1993). This anatomic diversity is of practical value especially for the identification of processed material, which can be helpful in trade disputes.
Knowledge of rattan anatomy has also been used to identify the structural features that characterize a "commercializable" cane, making it possible to analyse hitherto unused species for their processing potential (Weiner and Liese, 1991). For example, anatomic characterization suggests that rattans in the West African genera Eremospatha, Laccosperma and Oncocalamus have the same basic structures as the well-used Asian rattans, indicating that they should be suitable for furniture making, for which they have so far not been adequately utilized (Weiner and Liese, 1994).
The availability of raw material, especially of the valued species Calamus manan, is often defined as the most pressing problem for the furniture industry in the countries of origin, as well as in the main European furniture producing countries such as France, Germany, Italy and the United Kingdom. As the rattan ban has affected the development of the furniture industry within non-rattan producing countries, other countries such as Myanmar, Viet Nam, the Lao People's Democratic Republic and Papua New Guinea have increased harvesting of canes of varied quality. Much furniture is now designed to require only smaller-diameter canes. Factories cope by using low-grade canes, which are often stained and require colouring. A major rattan company in Germany with large furniture factories in Java, Indonesia, described the raw material shortfall, combined with the market price, as a decisive factor for further production (personal communication). For example, the trader may neglect early grading so that all possible canes can be obtained at a reasonable price.
The shortage of rattan has also led to partial or even total replacement of rattan furniture components by other materials such as plastic. The plastic "original imitation" rattan that is available on the market can be colourful, more economical in price and attractive in design.
Other major problems in rattan utilization are related to production technology, financing and marketing. There are many small rattan processors at the village level, who work with very simple tools, old-fashioned designs and limited skills. Their market access is restricted by the inferior quality of their products (Belcher, 1999).
For primary processing in the field, improved technologies for preservation and seasoning would reduce losses and improve the quality of the canes. Labour-intensive methods and simple low-cost procedures are often applied for peeling, splitting and bending. Technical improvements in the processing industry could increase the value of the products and thus also raw material prices.
Progress has been achieved in the areas of better hand tools and hardware, improved processing technologies and better finishes and colouring. However, structural properties, product relations, protection and waste utilization are still neglected areas of research. Indeed, the following priority needs for bamboo and rattan research were listed a decade ago in a report to the International Development Research Centre (IDRC) (Williams et al., 1991) and have hardly changed:
Finally, it is important to emphasize the need for marketing studies to identify the demand and determine what the market wants.
Bibliography
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