No information on copper is complete without considering perhaps its most famous characteristic, namely its beautiful and durable natural finish. Unlike the famous green patina associated with an exterior copper roof, the use of copper indoors creates the opportunity to take advantage of a palette of other finishes as well.
A prepatinated interior.
A beautifully formed and finished entryway.
As fabricated, or mill finish, is the most common mechanical finish. This is the way that sheet or strip copper will come right from the mill.
Mill finish starts as bright and very reflective. In an interior application, with proper protection, it can stay that way for a considerable time.
A polished, or specular finish, is mirror-like and highly reflective. A satin finish is subtle, and not nearly as reflective. Another common finish
is called matte satin. This is similar to the satin but with a degree more texture. A directional finish adds a grain to the metal.
Copper is also a very good material for embossing or stamping. Embossing adds a texture and imprints a pattern into the metal. Hammered
finishes give a very irregular surface that adds texture and shadows. Crimped copper adds shadows too, but it is very uniform appearing
as a small corrugation. These finishes may also be combined to create a unique overall effect.
Two examples of bronze railings and hardware.
Chemical finishes can be used to produce a wide variety of colours. Consider when the designer would like to have the green patina copper
is famous for, as part of an interior of some kind. Since copper will not weather naturally to a green patina in an interior environment,
prepatinated copper is manufactured using chemicals to achieve the green patina appearance. The preferred option is to buy prepatinated
copper from a metal service centre. This material should meet ASTM Specification B882, Prepatinated Copper for Architectural Applications. However, sometimes an installer or metal finisher is employed to spray chemicals on cold rolled copper material, in an attempt to induce a
patina appearance. This option has met with limited success, and it typically is not recommended.
An aged copper interior wall.
A third option would be to try to artificially age the copper some time after installation, but this also is not recommended because there is little chance of achieving the desired results.
A note of caution here. Prepatinated copper may become discoloured when touched or in contact with food or solvents, and it is very difficult
to clean. This should be taken into account during the planning process, when considering the use of this material.
A prepatinated interior canopy.
A fine example of prepatinated interior cladding.
Another chemical option is a brown tone, or oxidized finish. This may also be induced by applying chemicals to copper and some copper
alloys, but care must be taken and the work must be done in a controlled environment. Again, take into account the possibility of discolouration
as described for prepatinated copper. Custom colours, induced by chemicals, are also an option, and many artists and architectural metal
workers offer a wide range of custom colours. Because chemicals are used, extreme caution must be used and such work should
only be done by a qualified person.
The colour of this aged interior compliments the other materials used.
Paint is also an option, as copper is a good substrate for paint when properly primed. It is however seldom done, because typically copper requires very little maintenance and has a great, natural appearance. In most cases why would anyone choose to cover the copper with
Another option which can be considered for applications indoors is clear coatings. Clear coats help preserve the natural or mill finish. A clear
coat may be as simple as a coat of wax or as advanced as a hi-tech acrylic lacquer. The choice depends on the situation. Clear coats are typically formulated to keep the metal very reflective, and their use is also intended to prevent tarnishing of the metal from fingerprints and oxidation. One drawback is they are not permanent and will require maintenance over the years. Typically clear coats applied to an interior
feature will have a longer life than exterior applications, but they are subject to abrasion and may be susceptible to ultraviolet degradation.
A highly polished and coated detail.
Recently grey metallic coatings have been developed using a zinc/tin alloy applied over cold rolled sheet copper. It has a grey look which is
similar to lead-coated copper used for some exterior applications.
New innovations include composite systems which use sheet or strip copper bonded under factory conditions to a firm substrate such as
high-impact plastic. It is both firm and flat. The composite panel can be used for countertops, wall panels, ceiling panels, shelves and many
other applications. These systems are proprietary and the manufacturer's installation instructions must be followed.
Another option involves the use of copper alloys. Alloys have different properties than copper, and detailed data on strength, corrosion resistance, and so forth, is available from the CCBDA.
For decades copper alloys were identified by names. This was confusing and often resulted in the wrong material being used. Now the
Unified Numbering System (UNS) designation is used to accurately identify the materials in North America. In this section, the UNS designation
and previous name are included for illustration.
It should also be mentioned that the thickness of copper-alloy sheet and strip is measured in decimals of an inch and not in ounce-weight.
The following are some of the copper alloys commonly used for interior architectural applications.
C22000, Commercial Bronze, is copper with a 10% zinc addition, resulting in a reddish gold material colour. It is commonly used as strip, rod,
bar and wire.
C23000, Red Brass, has a reddish yellow colour, resulting from adding 15% zinc to copper. Strip, tube and pipe are most often used for
C26000, Cartridge Brass, consists of copper with 30% zinc, and its natural colour is yellow. Commonly used forms include strip, tube and
Alloy C26000 was the primary material used for this interior.
C28000, Muntz Metal, has a reddish yellow appearance. It is made by adding 40% zinc to copper, and most important, it can only be produced
as a flat rolled material (plate, sheet and strip).
Alloy C28000 was used extensively throughout this auditorium.
C38500, Architectural Bronze, is a colour match for C28000. As a result of a minor alloying addition, it can be produced as extrusions, bar
and rod, but not as flat rolled material. C28000 and C38500 are frequently used together for interior metalwork.
C65500, Silicon bronze, is copper with only 3% silicon added. It has a reddish gold natural colour, and is commonly available as plate, sheet,
strip, pipe and tube.
C74500, Nickel Silver, has a warm silver appearance, which some say has the slightest yellow tinge. It is produced by using 10% nickel with
a 65% copper and 25% zinc mix. Sheet, strip, bar, rod and tube are available.
Colour matching becomes important when combining different alloys in different forms to create an interior design. Information is available
from the CCBDA on which materials match when selecting sheet and strip, extrusions, tube and pipe, rod and wire, castings, fasteners, and
welding filler metals.