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Nomenclature
The principal architectural copper alloys, commercial
bronze 220, red brass 230, Muntz-metal 280, architectural
bronze 385 and the silicon bronzes 651 and 655 are generally
referred to in architectural parlance as “bronze.”
The nickel silvers 745 and 796 are commonly identified as
“white bronze’ while the other alloys are frequently
grouped under the heading “yellow bronze.” The
term “statuary bronze” is used to describe the
range of naturally weathered or chemically oxidized brown
to black surfaces. Patinas - both natural and artificial
are often called “green bronze.”
Historically and technically, bronze is defined as an alloy
in which the chief constituents are copper and tin; brass
as an alloy in which the chief constituents are copper and
zinc. Based on these definitions, only the casting alloys
containing two percent or more tin can be classified as
true bronzes. The other alloys, since they contain no tin,
are in reality brasses. The justification for calling these
alloys “bronzes” stems from the fact that they
resemble tin bronze in both natural and weathered colors.
Although the numerical designation system is used to identify
copper alloys, it is doubtful that the term “bronze”
which has connoted enduring beauty for centuries, will ever
be discarded from the architect's vocabulary - nor should
it be.
A Little About Brass
True brass is an alloy of copper and zinc. It tends to oxidize
(tarnish) quickly when exposed to air which is a major reason
why most brass is given a clear coating of lacquer to prevent
this condition. Most conventional polishes such as "Brasso
®", "Twinkle ®", etc. coat the raw
metal with a thin film of oil to inhibit the development
of future tarnishing.
Advantages of using brass
The use of brass provides an excellent, high class,
look. The advantages of brass for architectural applications
include its excellent corrosive resistance, and its joining,
plating, polishing and finishing characteristics. Brass
is easily machined.
Disadvantages of using brass
Brass requires a good deal of maintenance since
it is prone to a blackish tarnish.
Metal care tips for finished, lacquered brass
Most commercial metal polishes usually contain
solvents and detergents to remove the tarnish, mild abrasives
to polish the metal, and oils to act as a barrier between
the raw metal and air.
Brass products can turn "black" due to the over-use
or misuse of polish. The biggest challenge to upkeep most
metals, including brass, is the removal and inhibition of
tarnish. All substances, especially metals, oxidize when
exposed to air. Once tarnish is removed, a chemical barrier
should be created between the bare metal and the air to
inhibit the process from re-occurring.
Many people over-use and flood metal surfaces with polishes
thinking they are better protecting the surface. It is an
incorrect assumption that the use of more polish will provide
more protection. More polish creates a smudging problem
since fingerprints (human body oils) "dissolve"
the solvency of the metal polish. Additionally, too much
polish may discolor the surface.
Polishing
Apply a trace amount creating a thin film. Only apply an
adequate amount of metal polish and spread out the amount
on an absorbent rag. Then, let the rag dry out for 24 hours
before using on most metals. Apply this trace amount of
polish with the grain of the brass with one hand while buffing
it out in a rapid motion (creating friction) with the other
hand.
This burnishing, or buffing, action will harden the polish
and create a surface more difficult to smudge or discolor.
What not to do
Do not use heavy abrasives to clean brass.
Metal care tips for "raw" brass
The care of most raw metals is a 2-step process.
They are:
Step 1. Cleaning
To clean light soils use isopropyl (a.k.a. rubbing alcohol)
applied with the sponge side of a light-duty, "white-padded"
scrubbing sponge. In the event of tougher scuffmarks or
heavier soils, flip over the sponge and gently agitate moving
the white scrub pad with the grain of the metal.
Dampen the sponge side with water, and apply a light scouring
low abrasion cream onto it. Work the abrasion cream into
the sponge, and then stroke with the grain. When completed,
wipe the surface thoroughly clean with a clean, soft rag.
Once surface is cleaned, then go to the next step, polishing.
Step 2. Polishing
Use one of the best tools to polish brass, a "yellow"
treated dust cloth, which provides just the right amount
of oil onto metal. Wipe down the brass with this cloth and
then buff it dry with a soft, cotton cloth. The trace amount
of oil contained in the cloth should not smear or discolor,
especially after buffing.
Use olive oil. Rub brass with a cloth treated with olive
oil after each polishing and the brass will look brighter
and require less polishing. Olive oil retards tarnish.
What not to do
Do not use heavy abrasives to clean brass.
Popular Bronze/Brass Names & Compositions
Alloy 220
- Commercial Bronze - Nominal Composition 90% Copper, 10%
Zinc
Alloy 230
- Red Brass - Nominal Composition 85% Copper, 15% Zinc
Alloy 280
- Muntz Metal - Nominal Composition 60% Copper, 40% Zinc
Alloy 385
- Architectural Bronze - Nominal Composition 57% Copper,
40% Zinc, 3% Lead
Alloy 745
- Nickel Silver - Nominal Composition 65% Copper, 25% Zinc,
10% Nickel
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