Copper patina: the colour that time made.

In dry air, bare copper forms an oxide film within hours that the eye cannot yet see. Under moisture, oxygen and airborne pollutants that layer keeps growing, the metal loses its shine and turns an even brown. Only over years do basic copper compounds develop from it, the green patina. Patination reproduces that process in the workshop, so the intended state is there from the start.

Because precipitation stays on a pitched surface longer than on a vertical one. On external wall cladding the brown keeps deepening and usually stops at an anthracite brown, which is the final state there. On pitched roofs the layer develops further, up to the familiar patina green. Where pitched and vertical surfaces meet, a drip edge belongs in between.

On flat surfaces heavily exposed to rain, the strong green appears after roughly eight to fifteen years, depending on rainfall and the composition of the water. On the way there the surface passes through every intermediate stage from red gold through brown to anthracite. Anyone who wants the final state from day one has the surface patinated in the workshop.

We advise against it, and so does the German Copper Institute. Chemical colouring processes are intended for small objects indoors. Applied over large areas under site conditions the result is usually blotchy, and the layers created that way are generally not weather resistant: the natural process removes them again after a while. Copper sheets and strips patinated in the works, by contrast, come in consistent quality.

Patina consists of basic copper compounds, mostly carbonates and sulphates, near the coast also chlorides. It forms through air, moisture and carbon dioxide, adheres firmly and is harmless. Verdigris is a mixture of basic copper acetates and forms through acetic acid. It attacks the copper and is toxic. On a building it practically never occurs. The two are constantly confused but are different substances.

Yes. The layer adheres firmly, is stable in itself and renews itself where it is damaged. It slows further attack by air and moisture and is the reason copper roofs last for centuries. Copper is also resistant to building materials such as gypsum, lime and cement, and is not endangered by condensation.

No. Its composition depends on the air at the location, so it turns out differently from region to region. Near the coast a blue green tone often appears, in cities it stays dark brown for longer. The pitch and orientation of the surface play their part as well.

Yes. Rain running over an unsealed copper surface carries dissolved copper compounds with it. Where it meets pale materials such as natural stone, fair-faced concrete or render, greenish veils can form. Controlled water routing with drip edges and gutters avoids it.