What Is Patina?

How does patina form?

Patina forms when light, heat, air and handling slowly change the surface of a material, and it can also be applied on purpose as a finish. The three forms you meet in fashion are colour change in vegetable-tanned leather, tarnish on metal, and hand-applied colour on shoes.

On vegetable-tanned leather

Vegetable-tanned leather is made by soaking skins in liquors of tannin-rich bark, leaves and twigs. The Genuine Italian Vegetable-tanned Leather Consortium aged samples under a light source to mimic months or years of use, and found that temperature, heat and light all shifted their colour. It reports that the plant extracts used in tanning tend to re-emerge over time, pulling the colour towards brown, and that the change is most noticeable in the first two years of use.

The same study lists what decides the result on a real handbag, belt or pair of Oxford shoes: how often it is used, how much light it sees, the humidity it absorbs, and products such as wax and polish.

On brass, copper and silver

On metal, patina is a thin layer of corrosion product. The Canadian Conservation Institute (CCI) explains that polished copper darkens when sulphur-containing gases from pollution, rubber or wool react with it, and that brass, an alloy of copper and zinc, can tarnish too. CCI describes this tarnish, or patina, as black; green or blue-green signals more serious corrosion. Silver tarnish runs from yellow to red to blue before the layer turns black.

As an applied finish

Patina is also made deliberately. Merriam-Webster notes that the green film on copper and bronze can be formed artificially, for example with acids, and CCI notes that bronze is often a different colour because it has tarnished or been intentionally patinated. On leather shoes, the word also names colour applied by hand. Port magazine reports that Berluti’s colourists apply the house’s patina to its shoes by hand, and that the finish is designed to evolve as the shoe is worn.

On denim

Denim wearers apply a related idea to the fades that build up on indigo jeans with wear, for example on raw denim. Whiskering and distressed denim are factory finishes that imitate that wear rather than waiting for it.

What are the properties of patina?

Patina is a surface change that depends on the starting colour and on conditions of use, and it is hard to undo.

• It depends on use. The consortium names frequency of use, ambient light, absorbed humidity and wax or polish as the real-world variables.
• Starting colour matters. In the consortium's tests, natural, undyed leather changed the most and brown was the most stable.
• Light’s effect builds up. CCI warns that light damage to leather is cumulative and irreversible.
• Removing it costs material. CCI notes that cleaning with an abrasive polish can damage silver plating or surface detail.

How do you tell patina from damage?

Patina is an even change of colour or sheen on a sound surface; damage shows as powder, bloom, crusts or local spots. Use the table below with the piece in your hands.

Checks to make before you buy

• Rub a darkened area of leather with a fingertip. Red powder on your finger points to red rot, which CCI describes as a red, powdery surface.
• Look at a cut edge. A blue-green line can sometimes identify chrome-tanned leather, a different tannage from the vegetable-tanned leather described above.
• Check where brass fittings touch the leather. CCI notes that organic acids from coatings on leather can cause local green spots on copper alloys, for example on the buckles of a leather satchel.
• Read the stamp on silver. Sterling silver is 92.5% silver and 7.5% copper. E.P.N.S. means silver plate over nickel silver; E.P.B.M. means plate over Britannia metal. On plated jewellery, a different metal showing through usually means the plating has worn away.

When buying vintage leather or metal pieces, these checks help separate patina from deterioration.

How do you care for patina?

Caring for patina means controlling light, humidity and polishing more than adding products.

Leather

• Keep it out of direct sunlight and spotlights, which CCI says cause discolouration and drying.
• Aim for steady humidity: CCI recommends 45% to 55% relative humidity, warning that below 30% leather turns brittle and above 65% mould can grow.
• Remove dust with a soft brush.
• Treat dressings and conditioners as permanent. The US National Park Service accepts them on personal objects that must still function, such as work boots, but notes they can darken leather and cannot be fully removed.

Brass, copper and silver

• Clean only when necessary, using the softest abrasive that works, and rinse polish out of crevices.
• Handle polished metal as little as possible: bare hands leave fingerprints, which CCI says easily stain polished metal.
• Store silver in a sealed plastic bag, and keep metal away from damp, since CCI notes that damp air above about 65% relative humidity corrodes metals.