Teaching fungi to ‘draw’

A clock 1 metre in diameter made of spalted ash, beech and maple wood, used the soft rot fungus, Kretzschmaria deusta. The wood was manufactured under controlled conditions and is adorned by dark boundary lines, a unique specimen created by Empa’s industrial partner, Koster Holzwelten AG.

Fungi that decompose tree trunks can conjure up real works of art in wood. In nature, however, the decay-causing fungi not only decorate the tree but also destroy it.

Researchers at Empa, The Swiss Federal Laboratories for Materials Science and Technology, are now teaching fungi how to draw. The result is upscale, spalted wood that can be processed into design furniture, or even musical instruments!

Sometimes there is true beauty to be discovered in very unusual places. Like a Phoenix from the ashes, the coveted truffle beech made from rotting wood on the forest floor. Uniquely patterned, it has been much sought after as a raw material for furniture production since antiquity.

However, the search for natural truffle beeches is tricky. Even those who deliberately leave tree trunks to rot in the forest have to wait years before they can hope to obtain wood that is decorated with fungi-induced patterns and still usable.

‘Battle’ lines

Empa researchers have now developed a technology with which hardwoods, such as beech, ash and maple, can be specifically treated with fungal cultures so that the patterns in the wood can be controlled.

Dark dotting, winding lines and thin streaks of red, brown and black are known as zone lines. These are the interaction zones in which different fungi have erected barriers to protect their resources. They can also be caused by a single fungus delineating itself.

The fine black lines running through the wood are the traces of a battle. Sometimes they meander turbulently towards each other and separate small plots with a lightened background.

In other places, the dark drawings flow calmly as if they wanted to remind us of a boundary that none of the participants likes to cross. Fungi that have fought in a battle for territory and resources in the wood separate themselves from each other with pigmented lines.

With these demarcation lines, the fine threads of the fungal community not only protect their colony from other fungi but the black boundary also ensures that bacteria and insects stay away and the habitat retains an ideal amount of moisture.

What’s spalting?

Spalting is any form of wood colouration caused by fungi. Primarily found in dead trees, spalting can also occur in living trees under stress. Although it can cause weight and strength loss, the unique colouration and patterns of such wood are sought by woodworkers.

The process is divided into three main types: pigmentation, white rot and zone lines. Spalted wood may exhibit one or all of these types in varying degrees. Both hardwoods and softwoods can spalt, but zone lines and white rot are more commonly found on hardwoods because of enzymatic differences in white rotting fungi.

Brown rots are more common to conifers, although one brown rot, Fistulina hepatica (beefsteak fungus), is known to cause spalting among deciduous trees too.

Pigmentation is caused when fungi produce extra-cellular pigments inside the wood. Bluestain is also a form of pigmentation. However, the pigments are generally bound within the hyphae cell walls. A visible colour change can be seen if enough hyphae are concentrated in an area.

The most common groups of pigmentation fungi are the imperfect fungi and ascomycetes (sac fungi).

The mottled white pockets and bleaching effect, seen primarily on hardwoods, is due to white-rot fungi, which “bleach” by consuming lignin. Some white rotting can also be caused by an effect similar to pigmentation.

Brown rots, the “unpleasing” type of spalting, do not degrade lignin, thus creating a crumbly, cracked surface, which cannot be stabilised. Both types of rot, if uncontrolled, render wood useless.

Conditions required for spalting are the same as the conditions required for fungal growth: fixed nitrogen, micro-nutrients, water, warm temperatures and oxygen.

‘Teaching’ fungi

“We were able to identify fungi growing in nature and analyse them in the laboratory to select those with the most favourable properties as wood finishers,” says Hugh Morris, a scientist in Empa’s applied wood materials laboratory in St. Gallen, north-eastern Switzerland.

For example, the brittle cinder fungus and the Turkey-tail, when matched with each other, leave black lines caused by the pigment melanin and, at the same time, bleach the surrounding wood thanks to the fungal enzyme, laccase. “This creates a pattern with a particularly strong contrast in the wood,” explains Hugh.

Depending on the combination of fungal species, the lines are wild and impetuous, or almost geometric. The researcher is convinced that the fungi can even, in time, be trained to write words in wood!


By controlling the spalting process of various fungi, researchers have created pictures in the colonised wood such as a sunset (L) and a spalded bowl (R) by Krista Hilge.


The gentle bite of the fungi that are used in the Empa laboratory is particularly favourable. Despite their pronounced talent for drawing, the selected candidates hardly gnaw their substrata. “Although fungi generously supply the wood with pigments, the wood retains its stability and shape,” says Hugh.

However, the fact that the artistic process can be controlled and geared towards the desired result is not only owing to the type of fungus, the researchers also developed a process, with which the wood is ready for processing within weeks.

Conditions required for spalting are the same as the conditions required for fungal growth: fixed nitrogen, micro-nutrients, water, warm temperatures and oxygen.

Many applications

With the new technology, spalted wood can now be produced faster, more sustainably and with the desired marbling.

One of the reasons for this rather fast processing is that the selected fungal species can grow in the wood with considerably lower moisture levels. This means that the raw material does not have to be dried long, costly or energy-intensive before being processed into furniture.

Together with the industry partner, Koster Holzwelten AG, the researchers are now in the process of implementing an efficient and ecologically sustainable production method. This also includes the use of regional wood.

“Beechwood is a hardwood that is common in Switzerland, but appears uninteresting to furniture designers,” explains Koster Holzwelten’s Managing Director, Jakob Koster.

With spalted wood from local beech trees, however, it is possible to offer sought-after products on the Swiss timber market with an annual volume of around 3 billion Swiss Francs.

In addition to furniture, parquet floors and kitchen fronts, spalted wood can also be used for decorative objects and musical instruments. Unique pieces have always been created from patterned wood.



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