13 December, 2008

13. Dangerous Eaters of Wood

Most environments have dangerous things in them, but humans have proved quite efficient at eliminating the larger and more obvious hazards, such as other humans and larger animals. Until modern times, the persistent little beasties, like insects, have proved harder to stamp out. Some insects, together with some fungi, view the fabric of our material culture as a food source.

Builders in many parts of the world use plant stems, particularly trees, but also grasses and reeds, because they are relatively light and strong, tend to grow long and straight, and are often abundant. These plants have a structure built from a compound called cellulose. In wood this accounts for about 50% of the structure, the rest being hemicellulose and lignin. Cellulose and hemicellulose are polymers, chemicals formed by long chains of smaller base units. Cellulose is made from chains of glucose in much the same way that the plastic PVC (polyvinyl chloride) is made from chains of vinyl chloride molecules.

Cellulose is tough stuff, which is why we find wood so useful, and luckily it is also tough stuff to eat. For humans it would be pure dietary fibre, but we lack the appropriate bacteria in our gut to break it down. These are found in ruminants, like cows, and in certain insects, and it is the latter that are most likely to try and eat your house.

A termite, also known as 'white ant'

Compared to our venerable woodboring insects, like death watch beetle and other ’woodworm’, termites are in a different class as eaters of buildings and contents. Termites, also known as white ants, are voracious devourers of wood and other organic material, and they are endemic in tropical and subtropical regions. They like to consume wood as a colonial enterprise, and go about their business with a remarkable degree of caution and secrecy, surreptitiously eating wood from the inside out.

Termites can have a significant impact on traditional material culture. For example, parts of India do not have the same emphasis on wooden furniture and interiors that is typical in northern Europe. There is plenty of wood, and a tradition of woodworking that later became adept at producing furniture for western taste, but the presence of termites in the environment contributed to a greater emphasis on ceramics and stone in Indian building interiors. In Southeast Asia, timber, particularly for structural use, has to be chosen carefully, not just for its strength, but also for its ability to resist termites. Woods like teak and eucalyptus, with hard resinous heartwood, are preferred. Termites affect not only the used of wood in a culture, but also its preservation for archaeologists.
Dr Zahi Hawass and Dr Otto Schaden (left) at the official opening of KV63
One of the most exciting archaeological discoveries announced in 2006 was the finding of the first new tomb in Egypt’s Valley of the Kings since Howard Carter found Tutankhamun in 1922. Dr Otto Schaden, working in the area of another tomb, came across the vertical shaft, and it was named KV63, the sixty-third tomb found in the valley, Tutankhamun’s being KV62.
The tomb turned out to be a cache of material associated with mummification and other aspects of burial; clearly it was thought inappropriate to throw such materials away. The dryness of the tomb had preserved rare organic finds such as pillows and mats, but initial interest focused on seven wooden coffins, some with beautiful painted faces. On closer inspection, termites had attacked all but two, so that in places it was just the decoration that was holding the object together. This is a conservation nightmare, and stabilising these objects so that they can be removed from the tomb to lab, usually in pieces, is a slow and painstaking task. It has been suggested that the termites may have arrived from workmen’s huts constructed by later tomb builders, the same huts that hid this, and Tutankhamun’s tomb, for over 3000 years.

The fragile painted mask of a wooden coffin from KV63, badly damaged by termites
Egyptology is waiting to find out whose coffins they were, because intriguingly, any hieroglyphics on the coffins appear to have been painted over. While KV63 is from around the same period as Tutankhamun, interest has switched to the discovery of two new tombs nearby.
Tombs KV64 & KV65, one possibly undisturbed, were found in 2007 by Dr Zahi Hawass, the multi-award winning Secretary General of the Egyptian Supreme Council of Antiquities, National Geographic Explorer in Residence, star of Discovery Channel, and the only man on the planet who could give Indiana Jones a run for his money. I hope for the sake of archaeology that the KV64 Dr Hawass has found is different from the KV64 suggested by Egyptologist Dr Nicholas Reeves, using radar data, shortly before he was mysteriously run out of town by Dr Hawass.

It is the dryness of the Valley of the Kings that preserves so much fragile organic material, including mummies. However, much damage has been done to the tombs by flash flooding, and many poorly situated tombs have been virtually destroyed by these rare climatic events. The ancient builders may have included deep pits and shafts in the entrances to tombs to protect their occupants from floodwater, rather than simply to deter robbers.

Iron Age wood carving from a frozen Siberian Tomb

Organic materials tend to be preserved by very dry or very wet environments. In Northern Europe, mummies are found in bogs, and buildings and other timber structures are preserved in waterlogged conditions. Mention should also be made of preservation by extreme cold: bodies have been found preserved by glaciers and in remarkable frozen graves in northern Asia.

It is no coincidence that very dry, very cold, or waterlogged conditions are protection against fungi, often known as ‘dry rot’, that would naturally be reprocessing dead trees, but will happily imbibe timber in buildings if it becomes damp enough. Dry rot infections arise at about 30% moisture, and the fungi will eat the cellulose from the wood, leaving a brittle matrix of lignin. Ingress of water into a building is the commonest cause, and since prehistoric buildings contained significantly more wood than most modern buildings, they are vulnerable if not completely weatherproof.

It is small things like insects and fungi that pose real threats to a timber-built environment and help condition the architectural response. It is a complex collection of environmental stimuli that create a local architecture, which is why comparing buildings between different geographical regions requires considerably more caution than is sometimes shown by archaeologists thinking about these matters.

Further Reading:
STOP PRESS! Dr Hawass lecture:
[both accessed 12 October 2009]

Latest news on Valley of Kings
[accessed 12 October 2009]: http://www.kv64.info/

[accessed 12 October 2009]: http://www.kv-63.com/index.html

Zahi Hawass [accessed 12 October 2009]: http://guardians.net/hawass/