Why Handmade Metal Corrodes Differently

Walk past a mass-produced steel gate and a hand-forged one, both left bare to the weather, and you will notice something interesting: the wrought work often ages more gracefully, even though it rusts just as readily. That is partly chemistry and partly shape. Forge scale — the flaky blue-black oxide left by the hammer and the fire — offers a patchy barrier of its own. Hammered surfaces are also uneven, with hollows that hold water, and edges that cool and dry at different rates. Add the fact that each piece is unique, and you realise why a blanket approach rarely works. The goal is not to hide the metal, but to slow its decay without smothering the marks of the maker.

Preparation Decides Everything

No coating will hold on a dirty or damp surface, and this is where most rust prevention fails. Before you reach for wax or oil:

• Degrease with a solvent or a warm water and detergent wash, then rinse and dry properly.
• Remove loose, flaking scale and active red rust with a wire brush, abrasive pad or needle descaler. Tight, well-adhered grey-black scale can stay.
• Work outdoors or in a well-ventilated space — dust and solvent vapour are best kept away from your lungs.
• Warm the piece gently until it is just too hot to touch comfortably. Warm metal draws the coating into the surface rather than letting it sit on top.

Do not apply anything in cold, damp conditions. If the metal is below the dew point, moisture is already condensing on it and you are sealing that water in. A dry, mild day is worth waiting for.

Waxes: The Traditional Standby

Wax is the blacksmith's oldest friend and still the most sympathetic finish for interior and sheltered exterior work. A good microcrystalline wax — the conservation-grade paste sold in tins — gives a clear, dry, non-greasy film that lasts far longer than beeswax alone. Traditional recipes often blend beeswax with boiled linseed oil or turpentine to make a softer paste that spreads more easily over textured iron.

Application is simple but needs patience. Warm the metal, apply the wax thinly with a cloth, let it flash off, then buff with a stiff brush to work it into every hammer facet and scroll. Two thin coats beat one thick one. Expect to reapply every six to twelve months outdoors, and more often near the coast, where salt-laden air accelerates corrosion dramatically.

Oils and Oil-Black Finishes

Oil penetrates the porous surface of forged iron in a way wax cannot, which makes it ideal for tools, hardware and pieces with deep texture. Boiled linseed oil and tung oil both cure to a soft, amber-toned film that darkens and enriches with age. Applied hot to warm metal and then wiped back, they produce the deep satin black that characterises so much traditional ironwork.

• Boiled linseed oil — thin it with white spirit for the first coat, wipe off the excess, and cure in a warm, dry place. Store oily rags flat or submerged in water, since they can self-ignite.
• Tung oil — harder and more water-resistant, though slower to dry.
• Lanolin and specialist anti-corrosion sprays — excellent for hidden fixings, hinges and coastal installations, but too tacky for visible surfaces.

Paints, Lacquers and When to Use Them

There is no shame in paint. For exterior architectural ironwork in a damp climate, a properly applied paint system will outlast any wax by years. Use a zinc-rich or phosphate primer on bare steel, follow with a suitable topcoat, and build thin coats rather than one heavy one. Brush paint into the crevices and around fixings, and pay particular attention to the undersides of horizontals, where water sits.

Lacquers are a different matter. A clear acrylic or cellulose lacquer preserves a polished or blued surface beautifully indoors, but outdoors it traps moisture beneath scratches and can fail in patches. If you lacquer a piece that will live outside, be prepared to strip and refinish it periodically. For work that is meant to look hand-made, paint and lacquer have a further drawback: they fill the fine detail and soften crisp hammer marks.

Patinas and Deliberate Oxide

Rust is not always the enemy. A controlled patina can protect as well as decorate. Tannic acid applied to a lightly rusted surface converts red iron oxide into a stable blue-black tannate that resists further corrosion — a treatment long used on gates, railings and outdoor ironwork. Rust bluing, in which the piece is repeatedly rusted and then boiled, produces a deep, durable black finish on steel. On non-ferrous metals such as copper, brass and bronze, liver of sulphur creates rich browns and blacks that need only a wax topcoat to last.

Whatever route you take, reapply before the coating fails rather than after. Rust is far easier to prevent than to undo. And handle your work with clean gloves once it is finished — the salts on your fingers will happily start the whole process again.