Colour-changing chatoyance

The term ‘chatoyance’, or ‘chatoyancy’, represents a natural wood surface property, which consists of shifting colour depending on the lighting or observation direction. As many wood species exhibit this property, this sort of ‘dynamic appearance’ is well known to most woodworkers.


Fig.1 Chatoyance on different wood species

To experience it very clearly, a simple test can be conducted:

1) Source a small piece of timber from the list of wood species (Fig.1) with high or medium-high chatoyance;

2) Fine sand the surface or finish with shellac, oil or transparent epoxy resin;

3) Use a torch to illuminate it in a dark room, aiming to move the light around the entire piece and observing it from different directions.

You’ll notice a pleasant colour-shifting effect, which is often negligible under normal lighting conditions. This effect is due to the wood’s fibre microstructure, which, to some extent, acts as a multitude of microscopic mirrors; when these are reached in a certain direction, the surface appears much brighter. This behaviour is very difficult to detect on some species – such as olive wood – but can still be measured on all timbers.


1 Light in positions ‘A’ and ‘B’ with respect to the sample


2 Chatoyance on black walnut


3 Cypress – very low chatoyance


4 Iroko – very high chatoyance

Measuring chatoyance
Even if this phenomenon appears very difficult to explain in simple terms, it’s been well defined and described within different sectors. To understand the basic principle, imagine the situation shown in photo 1: a camera looks at a wood sample illuminated from two different positions – ‘A’ and ‘B’. In both, the light source is located at the same distance from the sample, and light hits the sample with the same incidence angle.

Photo 2 shows a first example of the result on a piece of black walnut, which has been sanded to 1,500 grit with no finish applied. It’s clear to see how the wood appears significantly brighter when illuminated from position ‘A’. The amount of brightness variation allows you to quantify how chatoyant a wood species is. Surface finish has an obvious impact on results: rough-sanded is hardly ever chatoyant, whereas one that’s been fine-sanded or finished with oil is often visibly so.


5 Simple curly maple tray


6 Curl on different species

The most chatoyant wood species
Measuring chatoyance allows you to compare various wood species, looking for those that are most – or least – chatoyant. Photos 3 & 4 demonstrate a comparison between two very different species: cypress and iroko. Obviously, all species have some natural variability; therefore, only a typical average value can be identified, still providing clear information as to where to find chatoyance. Systematic research carried out on thousands of samples from over 90 species provides an initial suggestion as how certain species will appear when used to make a piece of furniture, for example (Fig.1). This phenomenon is difficult to describe using words, but is easily demonstrated with animated GIFs, as collected on


7 Simple curly maple tray


8 Flecks on oak

Curl & other figuring
‘Curl’ is a typical type of figure that many wood species can exhibit, which is the result of a combination of properties: a wavy fibre distribution and some chatoyance. Photo 5 shows a classic curly maple example: a simple tray with evident stripes caused by chatoyance and fibre distortion. The same figuring is typically sought in violin backs, as pictured in the main photo. Photo 6 shows some further examples of curl: maple, followed by a piece of pearwood whose poor chatoyance fails to highlight fibre distortion, followed by movingui and koa, where high chatoyance makes curl particularly evident.


9 Flecks on London plane

Many other types of ‘figuring’ can be found in natural wood, which are caused by different types of fibre distortion – as depicted in photo 7. All these figures are, however, highlighted by chatoyance. Similarly, some very nice figuring is shown by species with evident ‘flecks’, or medullary rays, such as oak, London plane, beech or louro faia. Since medullary ray fibres are perpendicular to longitudinal ones, they appear brighter under lighting conditions that make longitudinal fibres darker, and vice-versa. This fascinating effect is demonstrated in photos 8-11.

Enhancing chatoyance
Finish has a significant effect on chatoyance; as an example, typical water-based floor finishes have a strong negative effect on this property. On the other hand, the following finishes work very well to enhance it:

• Shellac

• Linseed oil

• Transparent epoxy resin


10 Flecks on European beech

Other ways to enhance this includes:

Using a very sharp plane and avoiding sanding

Sanding the surface to a very fine grit

Cleaning the surface with alcohol prior to applying a finish


11 Flecks on louro faia

Finally, on light-coloured wood species, chatoyance can be improved by darkening the surface in different ways:

Sunlight exposure


Dyes, which penetrate deep into the cell structure and lend an otherwise flat piece a 3D effect.