Guide: Architectural Copper Work

Introduction

 
Pure copper (Cu from the Latin “cuprum”) is a soft, malleable metal with a high thermal and electrical conductivity and corrosion resistance. Its consistent use since man emerged from the Stone Age can be attributed to its wide array of properties which have provided inherent benefits in an extensive range of applications for over 10,000 years:
 

• Corrosion resistance – this longevity and resistance owing to its use in external settings historically and us being able to enjoy it to this day.
• Easily joined – by either soldering or brazing promoting coppers use in pipework systems and vessels or containers.
• Ductile – easily shaped and drawn into a variety of complex shapes and forms.
• Electrical and Thermal Conductivity – owing to its use in central heating systems and electrical wiring.
• Tough, – shatter resistant, copper was used in tools and weapons in ancient civilisations.
• Attractive – copper and its alloys have an attractive and varying hues from bright red to burnt orange and deep browns exemplified in jewellery, ornaments, and architecturally decorative applications.
• Easy to alloy – as many as 400 alloys of copper exist with the most well-known being brass, bronze and nickel allowing for adaptation of the metal to suit a variety of uses.
• Antibacterial – naturally hygienic, copper slows down the growth of germs owing to its use in hospitals, coins, plumbing systems and vast beer brewing vessels for years

 

Historical Context

Copper has been utilised by some of the oldest civilisations on record. Whilst no one knows exactly when copper was discovered, it is estimated at about 9000 years ago in the Middle East where a copper pendant dating to 8700BC was excavated.

Mining sites in present-day Israel, Egypt and Jordan date to around 4500 BC whilst in the UK, carbon dating has estimated mining established approx. 2600 BC. Some historians suggest it is one of the earliest metals to be worked by the human race, preceded only by gold and meteoric iron.
In ancient civilisations, copper was used for decorative embellishments, roofing and traditional fixings including nails and wires, whilst its stronger alloy bronze was reserved for weaponry and structural applications.

Extraction and production techniques have changed very little since ancient history.  Ores were crushed, roasted to remove organic components and then smelted. These initial stages produced a metal comprising approximately 30% copper (copper matte). Further refining processes, including passing oxygen through the matte and reacting it at high temperatures, prompted further transformation until the copper reached 98% purity (blister copper). Modern copper production includes a further and final refining process of electrolysis producing a copper of 99.9% purity.

Copper production underwent a major change during the Industrial Revolution. Output production rates improved massively in the 17th – 19th centuries due to the introduction of steam-powered pumps for mining and impurity removal from the ores in early production phases. New rolling techniques led to the development of sheet copper and its predominant use in decorative roof domes and cupolas.

Throughout history, the use of copper and its alloys has ranged from art, in statutory and pigmentation, to architectural features and industrial applications.

Its wide use in architectural features was predominantly due to the outcome of its corrosion. Probably copper’s most attractive and coveted trait is its natural changing display of colour from bright metallic tones to an assortment of browns, near blacks and finally its prestigious greenish patina.
 

Natural Patinas

The natural oxidisation process of copper, and its patina, is a particularly complex progression. As the copper oxidises, the metal undergoes a series of colour changes altering from oranges to darker tones as the oxide thickens. The rate of transformation depends on copper’s exposure to salts, moisture and acidity and the complete patination process can take anywhere from 7 – 30 years dependent on the environment.

The initial copper oxide layers can be noticeable from 6 - 9 months, providing a natural protective layer for the metal underneath. Within 5 years, cuprous and cupric sulphide films darken the surface to a brown and eventually slate grey. Continued exposure transforms the sulphide into sulfates, at which point the greenish patina develops.

 

Architectural Applications Past & Present

Copper unsurprisingly has an extensive history in architecture. Roofing, rainwater systems, domes, spires, vaults, leaded lights, weathervanes and wall cladding were all common applications for copper.

 

Roofing, Domes, Spires and Vaults

Malleable, characterful and durable, copper has been an opulent roofing material choice, predominantly featuring in British architecture from the 1800s onwards after the development of sheet production techniques.  
More decorative and complex roofing included curved surfaces and multi-faceted designs epitomised in domes, cupolas, spires and vaults.

Copper has been used in flashings due to its strength, ease of joining, ductility and long service life. Easy to hammer into watertight designs, copper allowed for roof construction without weak points.

Rainwater Systems

An attractive alternative to cast iron and its predecessor lead, copper provided strong leak-proof joints in rainwater systems. Highly corrosion-resistant, copper guttering can last more than 50 years.

 

Stained glass and leaded light windows

Traditional stained glass, where the pigment is painted onto the surface, involved the use of a paste comprised partially of copper. The glass was then heated to allow the pigment and glass to fuse together. Furthermore, the H section of leaded lights and stained glass were often held in place with copper wire instead of lead.

 

Ecclesiastical Adornments

Weathervanes were popular from the 9th century onwards due to a papal decree ordering a cock to sit at the summit of every tower or church steeple. Copper was the traditional material for their construction, and their popularity remained with the noble for centuries afterwards demanding more ingenious and humorous designs. Copper construction was superseded by wrought and cast iron in the 18th century.

Copper's capacity for a high polish led to its use in ecclesiastical embellishments for centuries. Grilles, gates, tombs, statues and altars were regularly covered with ornamental works using copper as an easily workable gild or enamel.

Typical Restoration Techniques

Through surveying, initial investigations and thorough reporting sufficient information can usually be generated to understand what intervention method is required. Conservation treatment and repair require high-quality materials and skilled and knowledgeable craftsmen.

The techniques employed when dealing with the conservation of copper artefacts will always be chosen dependent on the unique characteristics of the object or structure. Below are a few typical conservation approaches that are likely to be employed.

 

Cleaning

Care is always taken to avoid disturbing the natural patina that will have developed. In most cases, aggressive cleaning techniques such as galvanic, chemical or abrasive techniques, are neither recommended nor required.

Low-pressure water cleaning with a non-ionic neutral detergent is normally advised to remove pollutants and degraded surface coatings.
Where corrosion has occurred, low-pressure wet abrasive cleaning may be implemented or high-pressure steam cleaning to remove unsuitable coatings (e.g. linseed oil).

On external features subject to excessive water, such as fountains or rainwater systems, lime scale may build up and require careful removal by hand. Chemical cleaning methods require careful application and thorough neutralisation afterwards.

 

Artificial patination

A wide range of techniques is available to achieve artificial patination. However, this is rarely recommended as the patina may not develop at the same rate or to the same colour as the existing sections of copper. Leaving copper to patinate naturally is often the best course of action.

Repair methods

In conservation work, repair is always preferable over replacement and wherever possible will be undertaken. Intervention methods used will depend on a variety of factors including the historical context, structural requirements and form.

 

Riveting/Bolting

Often used to overlap joints where moderate strength is required, copper rivets need careful hammering to fit the holes and ensure a neat joint is produced with no splits. Prior to commercial availability, these rivets would have been made by the coppersmith from waste cuts folded and hammered to shape. 

 

Soft soldering

Soft soldering is a useful process for joining metals of many types, particularly small intricate parts which might get deformed or damaged with higher temperature processes. Soft soldering, which originally used a tin-lead alloy as the filler metal requires reasonably low temperatures to melt the filler but isn’t suitable for structural applications requiring compressive strength.

 

Manual Brazing

Using a bronze or brass (copper alloy) filler rod coated in flux, heat is applied on or near the joint in need of repair using a gas flame. To braze metals together a very tight joint must form so that the filler can be drawn in successfully. As such, this technique requires particularly high temperatures (around 600c) which isn’t always suitable when working with copper.

 

Silver soldering

A form of manual brazing using a filler rod made from silver alloy. The composition will vary, usually referred to as soft, medium and hard dependent on its melting temperature. The silver solder is absorbed by the two copper parts, resulting in a strong joint. The copper needs to be exceptionally clean, as repair failures are normally due to methods being applied over the patination layer and eventually breaking down.

Click below for further guides on typical fabric-specific conservation and restoration techniques employed: 

• Wrought iron restoration
• Cast iron restoration
• Lead restoration