Metals in Conservation
Metals are extremely versatile and can perform tasks that are impossible for other building materials. Each metal or alloy has unique characteristics and properties that govern how it can be used for architecture, art and ornament.
All metals traditionally used in buildings react with oxygen in the atmosphere in a process known as oxidation. Sometimes oxidation produces stable and protective patinas, but in other situations it can result in harmful corrosion that disfigures and seriously weakens the metal. Corrosion is usually a very gradual process and can often be slowed or prevented altogether by good maintenance and the use of protective paints and coatings.
Lead has been used in building since Roman times, and for many centuries it was the material of choice for the most prestigious royal and ecclesiastical buildings. It is generally very durable and can last hundreds of years. It can also suffer from serious underside corrosion leading to failure in as little as 15 years.
Historic England has undertaken extensive research to understand the causes of underside corrosion. You can read more about our research into the deterioration and conservation of lead on our page on Lead Roofs and Statuary: Understanding, Monitoring and Conservation.
Another threat to historic lead is theft. Roofs are often the target but thieves also take gutters, downpipes and lightning conductors. Such crimes leave buildings vulnerable to further damage through water penetration. Historic England works closely with the police and various church authorities to tackle this problem. Read more about our advice and guidance on dealing with metal theft from historic buildings on our page on Theft from Places of Worship.
Alternatives to lead
Following the theft of lead from a church roof, there may be occasions when re-covering the roof with terne-coated stainless steel, rather than lead, may be appropriate. This more closely resembles lead compared to other modern alternatives, is extremely durable and has little salvage value so is less likely to be targeted by thieves in the future. Historic England commissioned expert advice on some of the issues regarding the use of terne-coated stainless steel on church roofs. You can download a PDF of the guidance here:
Watch our Technical Tuesday webinar on Terne-Coated Stainless Steel: its use as a replacement material after lead theft from church roofs.
If you’d like to learn more about Historic England’s research to address the problem of rain-drumming noise on terne-coated stainless-steel roofs, you can read our report: Historic England Research Report 55/2021 - Rain Noise: Acoustic Tests on Terne-Coated Stainless-Steel Roofing.
Conservation of architectural metalwork
The field of architectural and structural metalwork encompasses a wide range of structures that vary in size, materials, significance and complexity: from engineering structures and bridges, to railings, rainwater goods or window frames, from fountains and statuary to catches, nails or simple hinges.
The webinar below covers what we mean by architectural and structural metalwork, the main metal groups (ferrous and non-ferrous), their properties and some typical problems, as well as a general approach to their conservation.
Conservation of iron gates and railings
Traditionally, gates and railings were made from wrought iron, cast iron and, later, steel. Sometimes the entire structure was made from a single type of metal, but in other cases different components could be in different metals (some in wrought iron and others in cast iron, for example). Regular maintenance is essential to keep iron gates and railings in good repair.
The webinar below gives an introduction to wrought and cast-iron gates and railings. It describes fabrication methods, as well as the properties of the different metals used and some typical features to help recognise them. Common condition problems, assessment and options for cleaning, repair, and coatings, as well as general advice on maintenance are also covered.
Looking after metal statuary
It is a common misconception that metal is a strong, tough material. In reality, the metal statues on our streets and in public squares are vulnerable to the weather, vandalism and long-term lack of maintenance. This guidance describes various types of historic metal statuary and common problems associated with it. It briefly explains methods of conservation and maintenance, and when to seek the advice of a metals conservator.
Historically, most metal statuary was made of bronze. To a lesser extent, lead, zinc, cast iron, copper and aluminium were also used to make statues and other large features, such as fountains.
Although metals have common properties, each one has unique physical and chemical characteristics that require specific conservation treatments.