How Natural Materials Age

Wood in the light: not everything darkens

Under UV light, the colouring substances in the wood surface change. How much and in which direction depends on the species.

Cherry is the most striking case. Freshly sanded, it looks light pinkish-brown; after six to twelve months by the window it is deep reddish-brown. The difference is so great that a cherry table on which a tablecloth lay for a year has two colours once it is removed.

Walnut goes the opposite way. Under light it loses its cool, greyish-brown tones and becomes warmer and lighter, which is often perceived as fading. On veneered surfaces the change is noticeable earlier than on solid wood. A veneer is usually only a few tenths of a millimetre thick, so the colouring zone lies directly at the surface and cannot be sanded off later. Solid wood is more forgiving in this respect.

Oak darkens slowly and moderately, usually towards honey. The same applies to all of them: anyone who partly covers a wooden surface will see the covering after a year. Occasionally moving objects on a tabletop costs nothing and prevents shadow marks.

The process cannot be stopped. Oils, waxes and lacquers with a UV filter delay the colour shift; they do not prevent it. The change is most pronounced in the first months, when a freshly worked surface receives light for the first time, and becomes less noticeable from year to year.

Teak turns grey outdoors without coming to harm

Teak naturally contains oils and tannins that protect it against moisture and fungal attack. They do not protect against UV radiation. Sunlight breaks down the lignin in the uppermost cell layer; what remains is cellulose, and that appears light grey to silvery.

The process is largely complete after about six to twelve months and affects only a very thin layer. The load-bearing capacity remains unchanged, so the greying is not damage, merely a surface layer.

Outdoors this is the development to be expected, regardless of whether the wood was freshly worked or reused. Anyone who wants to keep the warm brown tone has to maintain it actively: clean it and oil it once a year, twice in strong sunlight. The drawback is that this decision has a lasting effect. A piece that has been oiled and is later left to go grey looks blotchy for one to two seasons until the tone evens out.

Indoors this does not happen. Raw, untreated teak keeps its tone in the room as long as it does not stand permanently in direct southern sun. There, water rings and grease stains are more likely to show, because an open surface without a film remains absorbent.

Brass becomes dark where nobody touches it

Unlacquered brass is a copper-zinc alloy and reacts with oxygen and humidity. The surface first loses its bright shine, becomes a deeper golden brown and, in damp rooms, greenish in places. Sweat from hands accelerates this, because it is acidic.

This leads to something counter-intuitive: handles, edges and controls stay bright because they are constantly polished in use. Everything nobody touches becomes dark. After two years, a brass object therefore shows exactly how it was used.

The process can be delayed, not stopped. A dry location and occasional wiping with a soft cloth keep the surface bright for longer. Polishing pastes bring back the shine, but each time they remove a wafer-thin layer, which is why frequent polishing is not a good idea with thin brass plating.

Anyone who wants to avoid the change entirely needs lacquered brass. That, however, leads to the more unpleasant case: as long as the lacquer is intact, nothing happens. As soon as it has worn through at an edge, the metal oxidises in spots and the surface becomes blotchy instead of even. An open patina ages more beautifully than a damaged seal.

Leather stretches where people sit

Leather is skin and behaves like it. It absorbs moisture, releases it and adapts to load. Seats and backs give a little in the first months and form creases that remain even after getting up. That is not a weakness in workmanship, but the property that makes leather comfortable in the first place.

How strongly a leather develops a patina depends on the tanning and the finish. Vegetable-tanned, open-pored leathers darken noticeably under light and develop a sheen on armrests and seat edges that cannot be cleaned away. More heavily pigmented leathers change more slowly, but in return look the same for a long time and then suddenly worn.

One point rarely appears in care instructions: direct sun dries leather out long before a change in colour becomes visible. A leather armchair at a south-facing window needs distance or a curtain. Dry air from heating in winter also draws out moisture. One or two care treatments a year with a product suited to the type of leather are usually enough in living spaces.

Wool sheds, linen creases

A new wool rug loses loose fibres. With hand-woven rugs this usually takes four to twelve weeks, with very dense rugs longer. Dense wool rugs weigh around 2,500 grams per square metre and shed correspondingly longer than light flatweaves, simply because more fibre material has been worked into them. Vacuuming more often in the first weeks shortens the phase. The fluff is production residue, not a loss of substance.

In return, wool brings properties that pay off over the years. The fibre is naturally dirt-repellent, absorbs a lot of moisture without feeling wet, and largely recovers from pressure marks. Usually only the spots where the same heavy furniture leg stood for years remain visible.

Linen goes the other way: it becomes softer with every wash, because the pectins between the flax fibres dissolve. After ten to fifteen washes, a linen fabric has hardly anything in common with the stiff feel it had when new.

The price for this is creasing. Flax has little elasticity; the fibre breaks when folded and does not recover. Linen that does not crease is either blended or chemically finished. This is where things get uncomfortable: anyone who wants the drape and feel of linen has to accept the creases. You cannot have both.

Limestone takes on a greasy sheen where it is touched

Limestone consists mainly of calcium carbonate and, with a Mohs hardness of around 3, is a soft rock, softer than a knife blade. Travertine belongs to this group.

In places that are constantly touched, hand grease is drawn into the pores, and the constant friction smooths the surface. A darker, slightly shiny zone develops that feels different from the rest of the surface when you run your hand over it.

This can hardly be reversed, because the surface itself has changed. Impregnating it before first use slows the process down.

Limestone is also sensitive to acid. Lemon, vinegar, wine and many cleaning agents attack calcium carbonate and leave matt rings. Substance is actually lost in the process, so this no longer counts as patina. For cleaning, water and a pH-neutral agent are sufficient.

Patina is not wear

What applies to all these materials: they do not get worse, they change. The difference between patina and wear lies in whether the surface changes or whether material is lost. Patina follows use and destroys nothing in the process – it sits exactly where things are touched, or exactly where they are not. Wear is material that has been abraded, cracked or chipped off. One is part of the material. The other is damage.

The examples can be tested against the same criterion. The darkening of unlacquered brass, the sheen on a leather armrest and the greasy zone on a limestone edge are changes to the surface in which nothing is missing. A worn-through lacquer, a crack in the leather or a stone surface attacked by acid are not, because substance has been removed or destroyed there.