Oak, ash, walnut: three woods compared

Oak: the reliable one

Oak is hard, heavy and exceptionally durable. Its pores lie in rings, so it is ring-porous – the large earlywood pores form a clearly visible zone at the start of each growth ring, while the latewood next to it is denser and finer. This creates the striped grain that most people picture when they think of wood.

The colour ranges from pale yellowish brown to medium brown and darkens slightly over the years. Oak stands up to wear, can be sanded and oiled, and with a suitable finish scratches disappear almost completely.

One peculiarity worth knowing: oak contains tannic acid. In combination with iron and moisture, dark blue to black stains form. A wet metal watering can on an oak top therefore leaves more than a water ring. The same reaction is also used deliberately: so-called fuming with ammonia makes the tannic acid react and colours the wood dark brown deep into its structure.

This shows that the colour of an oak piece says little about the wood itself. Oiled, oak stays pale and warm; stained or fumed, it becomes walnut brown to almost black; limed or white-pigmented, it looks cool. Anyone who sees a dark oak surface is usually seeing a treatment and not the natural colour. Combined with dark metal, the visual difference from walnut almost disappears – in price and in how the wood behaves, it remains.

Oak is also the only one of the three woods that can hold up outdoors. This is down to the heartwood with its high tannin content, which is weather-resistant even untreated and turns silver-grey over time. The pale sapwood at the edge of the trunk does not have this protection and remains vulnerable. For outdoor use, therefore, what counts is not the species alone but which part of the trunk was used.

Ash: pale and elastic

At first glance ash looks similar to oak – it is also ring-porous and shows the same striped basic structure. However, it is considerably paler, often almost cream-white, and its figure is calmer and straighter. Its special quality lies elsewhere: it is unusually elastic.

That is why tool handles, ladder rungs, oars, gymnastics equipment and hockey sticks have traditionally been made from ash – it does not break, it gives and springs back. In furniture making this means that slender components are possible which would be too thin in a more brittle wood: thin chair legs, fine frames, curved backrests. Ash bends well under steam, which makes it interesting for rounded forms.

In furniture making, ash is widespread above all because it combines two things: the hardness of oak and a considerably paler base tone. Anyone who wants a solid, hard-wearing surface but does not want to darken the room almost inevitably ends up with it. Solid table tops are usually made between two and four centimetres (0.8 and 1.6 in) thick – thinner, a continuous solid wood board becomes prone to warping; thicker, it becomes unnecessarily heavy. Ash is priced roughly on a level with oak and considerably below walnut.

The drawback: ash is not weather-resistant. Its heartwood contains no significant protective substances, it readily absorbs moisture and is quickly attacked by fungi outdoors. Untreated, it therefore belongs exclusively indoors.

Walnut: the expensive dark one

Walnut is the premium wood of the three. Its colour spectrum ranges from greyish brown to chocolate brown, often with darker veins and occasionally violet or greenish nuances. Unlike oak and ash, it is diffuse-porous: the pores are distributed evenly across the growth ring, which is why the surface looks more even and softly figured rather than striped.

It is somewhat softer than oak and ash, moves less and can be worked very finely – sharp edges, fine profiles and carved details hold better in walnut than in ring-porous woods. The price is considerably higher than for oak and ash, because the trees grow more slowly, rarely grow in dense stands and yield less usable trunk wood.

That is exactly why walnut is often used as veneer. Thin sheets are sliced or peeled from a trunk and glued onto a substrate board. From the same amount of wood, this produces many square metres of surface instead of a few boards. This is not a trick but the usual, resource-efficient way of handling expensive woods – classic cabinetmaking has worked this way for centuries. What matters for quality is less the question of solid wood or veneer than the thickness of the veneer layer and the care taken in gluing: a cleanly veneered piece of furniture with a stable substrate board stays more dimensionally stable than a poorly made solid wood top.

One surprising point: walnut lightens rather than darkens with exposure to light. While oak darkens, walnut lightens over the years and loses its cool violet and grey-blue components, leaving a warmer, golden-brown tone. With all three woods, this change is uneven if only part of the surface gets sun – bowls, books or doilies show up after years as lighter or darker shadows. To avoid this, move objects on new surfaces occasionally during the first year.

Hardness compared

For the hardness of wood, the Brinell hardness has become established. It measures how deeply a steel ball penetrates the surface under a specified load; the smaller the permanent impression, the higher the value in newtons per square millimetre.

Oak and ash are roughly level here, at around 34 to 41 newtons per square millimetre. Walnut is somewhat lower. The widespread impression that oak is the hardest furniture wood therefore does not stand up to measurement – ash is in no way inferior to it, and the difference from walnut is smaller than its reputation as a soft fine wood suggests.

These figures are averages. Growing region, growth ring width and wood moisture shift them noticeably; slowly grown wood from cooler locations is usually denser. For everyday use, the finish is in any case more important than the hardness of the wood beneath it: a resistant lacquer layer protects a softer wood better than a thin oil protects a harder one.

Which wood for what

For heavily used surfaces – dining table, worktop, floor – oak and ash are the most robust of the three. For outdoor use, only oak heartwood is an option.

For pale, calm rooms and slender constructions, ash is the right choice. It is less expensive than walnut, paler than oak and visually the most restrained – where the furniture is not meant to be the lead, that is an advantage.

For a single dark anchor piece in a pale room, walnut is the most obvious choice – but rarely for the entire interior, because too much dark wood makes a room heavy. As a side table, sideboard or shelf, it adds an accent that carries a whole wall.

Anyone combining several woods in the same room should pay attention to the undertone rather than the lightness: warm yellowish and cool greyish tones clash, while woods of different lightness but the same temperature sit well side by side. And because all three change under light, nuances that jar at first often even out by themselves over the years.