Identify, Retain and Preserve
Identifying, retaining, and preserving architectural
metal features from the restoration period such as columns,
capitals, window hoods, or stairways; and their finishes
and colors. Identification is also critical to differentiate
between metals prior to work. Each metal has unique
properties and thus requires different treatments.
These early 19th century decorative metal window grilles have been retained and preserved. Photo: HABS Collection, NPS.
Altering architectural metal features from the restoration
Failing to properly document architectural metal features
from the restoration period which may result in their
Changing the type of finish, historic color, or accent
scheme unless the work can be substantiated by historical
Protect and Maintain
Protecting and maintaining restoration period architectural
metals from corrosion by providing proper drainage so
that water does not stand on flat, horizontal surfaces
or accumulate in curved, decorative features.
Cleaning architectural metals, when appropriate,
to remove corrosion prior to repainting or applying
other appropriate protective coatings.
The significant bronze doors are receiving
a protective coating of wax after cleaning. Photo: NPS files.
Identifying the particular type of metal prior to
any cleaning procedure and then testing to assure that
the gentlest cleaning method possible is selected or
determining that cleaning is inappropriate for the particular
Cleaning soft metals such as lead, tin, copper,
terneplate, and zinc with appropriate chemical methods
because their finishes can be easily abraded by blasting
Using the gentlest cleaning methods for cast iron,
wrought iron, and steel--hard metals--in order to remove
paint buildup and corrosion. If handscraping and wire
brushing have proven ineffective, low pressure grit
blasting may be used as long as it does not abrade or
damage the surface.
Applying appropriate paint or other coating systems
after cleaning in order to decrease the corrosion rate
of metals or alloys.
Repainting with colors that are documented to the
restoration period of the building.
Applying an appropriate protective coating such
as lacquer to an architectural metal feature such as
a bronze door which is subject to heavy pedestrian use.
Evaluating the existing condition of the architectural
metals to determine whether more than protection and
maintenance are required, that is, if repairs to metal
features from the restoration period will be necessary.
Failing to identify, evaluate, and treat the causes
of corrosion, such as moisture from leaking roofs or
Exposing metals which were intended to be protected
from the environment.
On this building, a strong alkaline paint remover
was used, and apparently was not adequately rinsed
or neutralized. Over a period of months, the newly
applied paint began to peel and streaks of rust
appeared on the iron. Photo: Kim Lovejoy.
Applying paint or other coatings to metals such as
copper, bronze, or stainless steel that were meant to
Using cleaning methods which alter or damage the historic
color, texture, and finish of the metal; or cleaning
when it is inappropriate for the metal.
Removing the patina of historic metal. The patina may
be a protective coating on some metals, such as bronze
or copper, as well as a significant historic finish.
Cleaning soft metals such as lead, tin, copper, terneplate,
and zinc with grit blasting which will abrade the surface
of the metal.
Failing to employ gentler methods prior to abrasively
cleaning cast iron, wrought iron or steel; or using
high pressure grit blasting.
Failing to re-apply protective coating systems to metals
or alloys that require them after cleaning so that accelerated
Using new colors that are not documented to the restoration
period of the building.
Failing to assess pedestrian use or new access patterns
so that architectural metal features are subject to
damage by use or inappropriate maintenance such as salting
Failing to undertake adequate measures to assure the
protection of architectural metal features from the
Repairing, stabilizing, and conserving fragile architectural
metal from the restoration period using well-tested
consolidants, when appropriate. Repairs should be physically
and visually compatible and identifiable upon close
inspection for future research.
Structural cracks, gaps at joints between components,
and a large opening where part of the console
bracket is missing are the problems evident in
this cast-iron assembly. Photo: Ford, Powell &
Repairing architectural metal features from the
restoration period by patching, splicing, or otherwise
reinforcing the metal using recognized preservation
methods. Repairs may also include the limited replacement
in kind--or with a compatible substitute material--of
those extensively deteriorated or missing parts of features
from the restoration period when there are surviving
prototypes such as porch balusters, column capitals
or bases; or porch cresting. The new work should be
unobtrusively dated to guide future research and treatment.
Removing architectural metal from the restoration period
that could be stabilized and conserved; or using untested
consolidants and untrained personnel, thus causing further
damage to fragile historic materials.
Replacing an entire architectural metal feature from
the restoration period such as a column or a balustrade
when repair of the metal and limited replacement of
deteriorated or missing parts are appropriate.
Using a substitute material for the replacement part
that does not convey the visual appearance of the surviving
parts of the architectural metal feature or that is
physically or chemically incompatible.
Replacing in kind an entire architectural metal feature
from the restoration period that is too deteriorated
to repair--if the overall form and detailing are still
evident--using the physical evidence as a model to reproduce
the feature. Examples could include cast iron porch
steps or roof cresting. If using the same kind of material
is not technically or economically feasible, then a
compatible substitute material may be considered. The
new work should be unobtrusively dated to guide future
research and treatment.
The Standards for Restoration call for the repair
of existing features from the restoration period
as well as the re-creation of missing features
from the period. In some instances, when missing
features are replaced, substitute materials may
be considered if they convey the appearance of
the historic materials. In this example at Philadelphia's
Independence Hall, the clock was re-built in 1972-73
using cast stone and wood with fiberglass and
polyester bronze ornamentation. Photo: Lee H.
Removing an architectural metal feature from the restoration
period that is unrepairable and not replacing it.
The following Restoration
work is highlighted to indicate that it involves
the removal or alteration of existing historic
architectural metal features that would be retained
in Preservation and Rehabilitation treatments;
and the replacement of missing architectural metal
features from the restoration period using all
Removing Existing Features from Other Historic
Removing or altering architectural metal features
from other historic periods such as a later cast
iron porch railing or aluminum windows.
Documenting materials and features dating
from other periods prior to their alteration or
removal. If possible, selected examples of these
features or materials should be stored to facilitate
Failing to remove an architectural metal feature
from another period, thus confusing the depiction
of the building's significance.
Failing to document architectural metal features
from other historic periods that are removed from
the building so that a valuable portion of the
historic record is lost.
Re-creating Missing Features
from the Restoration Period
Re-creating a missing architectural metal feature
that existed during the restoration period based
on physical or documentary evidence; for example,
duplicating a cast iron storefront or porch.
Constructing an architectural metal feature that
was part of the original design for the building
but was never actually built; or constructing
a feature which was thought to have existed during
the restoration period, but for which there is