Bamboo and Rattan/Bamboo/Course-4 Unit-1
Block – 1: Bamboo Products Unit 1 – 'Bamboo Products: Design Aspects - their relevance''
Bamboo: Material for the Future
There is a growing pubic and private demand globally for low-cost, environmentally friendly and socially balanced products, systems and lifestyle options.
Bamboo is a material that fulfils all of these criteria, since it is highly renewable (can be harvested every year unlike a tree, which can be cut only one) and environmentally friendly (absorbs more carbon dioxide than most trees, binds topsoil to prevent erosion and puts nutrients back into the soil, conserves groundwater and prevents water runoffs). It is also a viable alternative to timber and thus helps reduce deforestation, and can create livelihood opportunities for both rural and urban poor.
The investments required in capital, tools and machinery and raw material for bamboo-based enterprises are low when compared with those for other micro, small and medium enterprises. Bamboo-based production can play an important role in providing a long-term source of income and employment to individuals ranging from bamboo farmers to processors to entrepreneurs. These special qualities of bamboo have been recognized all over the world. In the domestic market, both the private and public sector institutional sectors – such as government departments, schools and tourism sector – have shown interest in the use and promotion of bamboo as a material. In the international scene, there is a keen interest from designers on bamboo, especially reconstituted bamboo, utilized in a contemporary context.
For these reasons, bamboo is a material poised to have a strong foothold in the export and domestic markets.
Why is it important to have ‘designed Bamboo Products?
Market studies have indicated the large demand for bamboo products in both the domestic and international markets in diverse market segments. However, most of the current bamboo products are present only in small, specialized markets and low-cost markets. Despite the high volume of production, the bamboo products currently being produced are not being absorbed into larger markets. This indicates that these products are not able to compete with other products.
For this we need to understand a bit more about what ‘design’ entails.
What is Design? A person who does not have a design background would connect the term ‘design’ with different things. For example:
Design is about Art – sketching or painting pictures.
Design is about Fashion – creation of clothes in new styles and patterns.
Design is about Craft – creating aesthetic objects based on traditional styles and techniques.
In fact, design is not limited to any of these factors, but includes all of these and more. Design is a process that integrates different and diverse disciplines, such as production and marketing, which are closely related to products, as well as disciplines such as botany and the social sciences, depending on the specifics of the design problem being dealt with.
Design is a problem solving tool. It is a process or a methodology to arrive at the best solution for a given problem. This design decision is identified through a process that comprises research, analysis and synthesis.
To take the best design decision, like any other decision, we must know all the parameters and limits of the issue to be resolved.
Key issues in bamboo-based product development
The key issues in bamboo-based product development are:
o Bamboo resources
o Other resources
Production and processing resources
o Economic resources
o Processors/skill levels
Bamboo is member of a tribe of grasses called “Bambuseae”. This large group of giant, fast-growing grasses are “woody” or wood-like and that is what makes bamboo so useful to us. There are more than 1,200 different bamboo species in about 100 different kinds (genera). Each species of bamboo has different characteristics.
All bamboo species have cylindrical, woody stems or “culms”. One interesting characteristic of a culm is that it first grows in girth before growing in height! When a bamboo culm emerges from the soil, sprouting from the underground stem called rhizome, it would have almost reached its maximum diameter, which can go up to 30 cm. Rest of the growth is mostly in height, which can be even 40 m. The culms of every bamboo species have the maximum diameter at the base and tape towards the tip (apex). By water pressure, the culm is pressed out of the soil segment by segment. The branches and leaves come out of the culm at a later stage. Most culms would “mature” in 3-4 years. A culm is made of several segments, separated from each other on the inside by a wall (called “septum”). These points of separation are called knots or “nodes”. Bamboo culms are particularly strong at their nodes. The part between two nodes is called “internode”. This internode is usually hollow and air-tight (that is why bamboo culms make good rafts), though there are some bamboos that are solid.
The culm is the part of bamboo most used for production. A designer needs to understand, in great detail, the nature of the culm before starting the design process.
There are two approaches to the usage of bamboo. One is to design the product and then to find a bamboo species that matches the product’s requirements, and the other is to identify the species that is easily available and then to design a product according to the characteristics of the bamboo.
Let us now look at the features of the culm that are important for design process.
Culm diameter: Culm diameter, which can be anywhere from 30 cm to less than 1 cm, is very important when designing a whole or round bamboo product, i.e. when using the bamboo in its natural, cylindrical form. The culm diameter dictates the usage of the material and the aesthetics of the product in certain cases. For example, the large culm diameter of the Giant Bamboo (Dendrocalamus giganteus) allows for constructing large cylindrical elements such as flower pots or umbrella stands from the culm, without joining any additional component. In a bamboo like the Reed Cane (Arundinaria gracilis), for example, the small culm diameter does not allow even a pen holder to be made from the culm without joinery of some kind, though it does allow a bamboo pen to be made, which would not be possible as simply with a bamboo of larger diameter.
Culm diameter is also a factor to think about when using the bamboo in flattened form – when the freshly cut culm is opened up by scraping the outside wall until thickness is about 1–1.5 mm and then this thinned down culm is split along its length with a single slit. The culm is then ‘opened out’ using heat, which results in a paper like strip, where the circumference of the culm is the width of the strip. The bigger the diameter, the larger is the circumference. This is the reason why larger diameter bamboos are preferred to make ‘flattened’ bamboo products like traditional steamers.
Sometimes, bamboo culm is given a single slit to open it, and then the entire culm is crushed. Here too, as in the case of flattened bamboo, the width of the flat crushed strip is the same as the circumference of the culm. When making bamboo boards or when attempting to cover large areas with crushed interlaced bamboo strips, the diameter of the bamboo is important, since the bigger the diameter, the wider the strip. When a bamboo of a smaller diameter is used, the production cost increases, as more number of culms will need to be opened up or crushed.
When making splits (lengthwise sections of culm) or slivers (lengthwise sections of splits), a bamboo with a larger diameter is preferred to a bamboo with a smaller diameter. This is for the simple reason that a thicker culm will have more material for more splits or slivers from the same length of bamboo, and would therefore be more economical from the production angle. Culm diameter is also important when we make splits or slivers for interlacing. To make wider splits or slivers, culms of a larger diameter are required, otherwise, the splits or slivers will not be fully flat.
Culm wall thickness: Culm wall thickness of bamboo culms range from just 1 mm to more than 8 cm. Some bamboos, like Calcutta Bamboo or Solid Bamboo (Dendrocalamus strictus), are ‘solid’ – the hollow part of the internode is negligible or non-existent and therefore, the culm wall is very thick. A greater culm thickness means that the bamboo will be heavier (but stronger too) than a thin-walled species of the same size.
When making splits or slivers, a bamboo with a thicker wall is generally more cost-efficient from the production point than a bamboo with a thinner wall. This is because the additional material in the thicker wall allows for more splits or slivers from the same length of bamboo.
Thicker-walled species are also preferred when joinery is an important part of the product, since a thicker wall allows for more material at the point of the joint. In a thinner-walled species, additional materials like wood may need to be used to reinforce the hollow culm at the point of the joinery.
Solid bamboos are useful when all components need to be standardized and of the same size. Short bamboo sections of under 3 feet can be turned on the lathe to achieve uniform and symmetrical components. As with wooden lathe turned products, perfect cylinders as well as curved silhouettes are possible by this technique.
Thinner-walled species with larger diameters are preferred for flattening. The wall thickness of a culm needs to be not more than 1.5 mm at the time of flattening. Generally, the outer portion of a culm’s internode are scraped away until this dimension is achieved. With a thicker-walled species, the material thus removed would be more as compared with a thinner-walled species. Therefore, the same product from a thicker-walled species would indicate a greater cost of production because of the higher material wastage and increased processing time.
Internodal length: As said earlier, the portion between two adjacent nodes – the internode – is usually hollow. The internodal length varies from species to species, and can be anywhere between the average of 30 cm and the extreme of 150 cm. The internodal length is very important for products that use a lot of slivers in their construction, such as handicrafts. The node or ‘knot’ of bamboo is generally avoided when producing interlaced products, and that means the length of the sliver, or slat depends on the length of the internodal portion of bamboo. Since the wall thickness is more at the nodes, the inclusion of the knots makes the slivers uneven. The skill required to interlace/weave uneven slivers is greater. The use of longer slivers makes the product aesthetically smoother and uniform, as the number of joints while interlacing is reduced. Use of longer slivers also makes the production time- and cost-effective. Hence, bamboos with long internodes are preferred for interlacing. Bamboo species with shorter internodes – like Bambusa balcooa and Phyllostachys pubescens – are preferred when using the culms as structural load-bearing members. The septum at the node is a reinforcing connector and therefore, the closer the nodes, the greater the strength of the bamboo.
Species with longer internodes are also preferred in applications that require long hollow ‘tubes’ or cylinders, such as containers (long body), water tubes (less septums to break), panels (less knots in the pattern), etc.. A common method of making containers is also to split the bamboo culm into two equal parts and use the part between two nodes as the container – such as when making shallow serving vessels. When the length of the container desired is short, a species with short internodes is desirable.
Species with longer internodes are also preferred in shapes that involve bending, such as an angle or a circle. As the fibres are denser around the node, the behaviour of the material at the internode and node will differ during bending. A circle needs to be completely symmetrical, so if possible, the node should be completely avoided in its construction. If the node is used, there is a strong likelihood that there will be an asymmetrical warp or bend at the area of the node. Behaviour of culm after drying: Each bamboo species behaves differently once it is dry. This is a very important property of the culm, since generally, there is always some amount of drying that happens even after the finished product is completed. In the case of interlaced products, the drying period would be more, since the slivers for interlaced products are relatively greener, than whole bamboo furniture, for example.
Shrinkage after drying is a very important factor and needs to be allowed for wherever possible. In the case of interlaced products such as bamboo mats, the mat is likely to loosen after drying, since each sliver will shrink. This can be countered by interlacing only after the slivers are dry.
When making furniture or other products where the components are mostly of round bamboo, it is better to use completely dry and “seasoned” bamboo. If green bamboo is used, the dimension of the final product may change, and the joints may get loosened due to shrinkage on drying. Even an alteration of a few millimetres can cause an entire consignment of products to be rejected if the market is strict, such as the export market.
Warping after drying is also common among certain bamboo species such as the Tufted Bamboo (Dendrocalamus hamiltonii), especially when the culm is not used in round form but as splits or slivers. Completely straight green splits or slivers can warp in a serpentine manner on drying, especially at the node. There is not much we can do about this, unless we use controlled drying using low heat and lot of air, thereby increasing capital investment and production expenses. This characteristic of certain bamboos needs to be kept in mind while designing. Unless the serpentine warps are desired, one should stick to making whole or round bamboo products or completely reconstituted bamboo products from such species.
Culms generally do not retain the green outer colour after they dry. This needs to be kept in mind while designing bamboo products, because the green colour of bamboo, which is often desired in bamboo products and which imparts natural aesthetic, changes when the bamboo dries. The products that look fresh and green become a pale yellow to brown colour when dry. To avoid this later disappointment, one needs to look at a dry culm of the species to understand how it will look on drying, and then take design decisions accordingly. Application of chemicals like copper sulphate may delay the drying period, but drying is unavoidable.
Culm shape: The culms of every bamboo species have their maximum diameter at the base, i.e. at ground level, and taper towards the apex. This means that every bamboo culm is an elongated cone, but it is so elongated that the culm diameter is reasonably consistent throughout its length. In general, all culms are round, though a few species have very distinct culm cross sections – the exotic Buddha Belly bamboo (Bambusa wamin), which has bulbous segments, or the Square Bamboo (Chimonobambusa quadrangularis) known for the squarish shape of its culm. These bamboos, however, have their odd shapes restricted towards the bottom part, and tend to regain the round shape in the higher segments. Another relative of the Square Bamboo, the Walking Stick Bamboo (Chimonobambusa tumidissinoda) has relatively round culms, but very prominent nodes that are much thicker than the internode. Certain varieties of otherwise regular bamboos have asymmetrical culms, with one side tending to be flat. Some bamboo scientists say that such oddities result from environmental stresses and may not continue beyond a generation in natural conditions.
Certain bamboos may not have straight culms: two well-known species – Bambusa bambos and Guadua angustifolia – are known for their crooked culms. This is because both these bamboos are thorny and heavily branched, and grow in thick clumps so that the branches of adjacent culms intertwine. During the course of growth, culms exert pressure on each other, causing the stems to grow crooked. To remedy this, when these species are grown in plantations, their lower branches are pruned early. Such characteristics should be kept in mind before working with any species of bamboo, as the perfection or imperfection of the culm shape is of utmost importance. Moso Bamboo (Phyllostachys heterocycla var. pubescens), for example, a species widely grown and used in China, is almost perfectly straight and symmetrical. Therefore, it is very production friendly, including for industrialized production.
The circular or near-circular cross section of most bamboo culms is sometimes a restricting factor in their usage as whole culms. This is may be why other cross sections, like a square cross section of bamboo, have been much researched and in demand. It is possible to grow bamboo in cross-sections other than circular through a simple technique that involves placing a strong tube of the desired cross section like a mould on a healthy new shoot. This mould should be slightly smaller than the culm’s natural diameter and should be around 1.5 m in length. The soft shoot is constricted by the mould and so takes on its shape as it grows. Every few days, the mould/tube is moved higher up as the culm grows. In this manner, culms of square, triangular, oval, or other cross-sections can be ‘extruded’ while they grow from shoots. Culms formed in this manner hold this shape throughout their life span.
The technique cannot be controlled totally as it is applied only on fresh shoots, which emerge during the monsoon season, to take advantage of the spurt in growth. Because of this, the survival rate of these ‘extruded’ culms is about one in four.