Caring for Your Iron & Steel
Surface finishes on iron & steel
Iron and steel surfaces may be polished to a mirror finish, chemically or heat-treated to make the surface blue (blueing, used on watch springs, weapons, and many other items), brown (browning, used on shotgun barrels among other things), or to bring out the pattern on watered steel or on pattern welded steel. These surface finishes are often very thin layers, and can be worn away by over vigorous cleaning with harsh abrasives. Once lost, they can only be brought back by chemical treatment carried out by a professional.
Iron was also plated with other metals such as tin, (and more recently zinc and chrome) for protective reasons, or brass for decorative effects.
Iron corrosion requires moisture and oxygen and will be exacerbated by high relative humidity and contact with acids or alkalis (from fingerprints, pollutants etc.). There are different types of iron corrosion. Some are considered benign, for example black compact 'tarnish' whilst others are more actively cause damage, for example orange-red rust. Iron corrosion products are larger than the metal they are formed from, so they tend to form flakes or crusts. However, corrosion will also eat into the surface, leaving behind a pitted surface when it is finally removed.
Removing rust from cutlery
Please read the Basic Guidelines page before attempting to clean your object.
The aim is to gently remove the corrosion products that protrude from the surface. Unless the corrosion below the surface is very powdery (active) and must be removed for the stability of the object, removing corrosion products from below the surface will leave unsightly pits. On bright polished surfaces such as knife blades, the aim is to remove as much corrosion as possible without leaving unsightly bright scratched patches.
In the case of a heavily corroded knife blade, it may not be possible to remove enough corrosion products to render the knives serviceable. Don't be tempted to use more radical methods - consult a conservator, who can advise you whether the original blade is salvageable or should be replaced.
- If the knife handle is not iron, for example, bone or ceramic, cover it with Clingfilm to prevent staining. This is to help prevent solvents or cleaning materials from affecting the resin that may have been used to hold the tang of the blade in the handle. For the same reason, avoid immersing the knife and make sure that solvents don't come into contact with the handle.
- Make a cotton wool swab, moisten it with white spirit and rub over the whole blade to remove dirt, grease and some corrosion products.
- Use the wooden kebab stick itself to rub gently at the corroded patches.
Use a small amount of a mild abrasive cream on a cotton swab to rub gently at the corroded areas. Take care to rinse with white spirit frequently and check that you are not creating bright patches.
- If the corrosion is very resistant, the last resort is to use wire wool. The wire wool must be extremely fine - use only 0000 grade. Take a small amount of the wire wool, and wrap it round a kebab stick to make a swab, moisten it with white spirit and gently rub the corroded area, rinsing frequently with white spirit. Pre-soaking the corrosion in white spirit can soften it and aid removal.
- Wipe over the surface with a swab dampened with white spirit, and then with a swab dampened with methylated spirit to remove residues.
- If the object is to be displayed, you could complete the treatment by applying a wax coating. Otherwise, simply store in a dry, cool place away from pollutants etc.
Treating iron & steel with a surface finish
All coatings, whether metal plating, wax, or 'passivating' layers, will only be effective in stopping iron corrosion occurring if there are no breaks, cracks or holes in them. Because corrosion products are more bulky than the metal, they can push up from underneath, causing bubbles, and may come through gaps in the coating and spread out on the surface. The only way to get rid of all this iron corrosion is to remove the coating and then remove the corrosion beneath. However, if the coating is original to the object, this radical step is rare because much of the art historical, aesthetic and monetary value of the object will reside in the original surface.
Surface finishes, such as blueing, are extremely fragile and corrosion on the surface will destroy the finish - removing corrosion will reveal bare metal underneath. Corrosion products can also disrupt inlays by pushing the inlaid metal up. If you have objects displaying these kinds of problems, consult a conservator as treatment is often quite complicated.
Painted iron and steel objects are relatively common, but occasionally there are valuable examples. If you have a painted iron piece (child's toy, pram, sledge, commercial signs etc.) find out whether it is a rare example. Stripping the paint from a rare piece will rob it of much of its historical and monetary value.
Household objects such as firegrates, fenders and fire irons are easier to treat. In the past, blacking was used, applied with a brush. This concoction, which contained black lead, could also contain an abrasive element to remove any corrosion and left a protective finish on the iron. However, maintenance is required, and corrosion will occur if the object is left for long enough in poor environmental conditions.
Outdoor iron objects are nearly always coated because of the harsh environmental conditions to which they are exposed. They may be painted, galvanised (coated with zinc), or have had heavy duty oils or waxes applied. There are products available to protect pieces like these, but a conservator should be consulted before treatment is attempted, in case there are remnants of previous paint schemes that have historical interest or importance.