Preservation Note 5

On-site Bronze Refinishing

Metals

July-91

Metal Restoration and Cleaning-05900

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The following specification provides two on-site methods for recreating
either a rubbed/satin or mirror finish on architectural bronze. Use
these techniques to:

1\. Restore a damaged or worn historic finish to its original uniform
texture and gloss

2\. Smooth a contemporary brushed finish on new or inappropriately
refinished historic bronze

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Check the building\'s Historic Structure Report (HSR), \"Description as
Originally Built\", to identify the original bronze finish. HSR\'s for
most historic buildings are available in the GSA-NCR Technical Resources
Library, Regional Office Building, 7th and D Streets, SW., Washington,
DC (202) 708-6278. If no HSR has been prepared for the building, retain
an architectural conservator to examine the bronze and determine the
correct historic finish(es). Insert Sections 1-3 (below) into
refinishing specifications for each type of finish (rubbed/satin,
mirror) to be replicated.

See Preservation Notebook No. 4, \"Bronze Finishes\", for additional
information on bronze finishing nomenclature and factory finish
specifications.

COMMON CSI SPECIFICATION LOCATIONS:

05700 ORNAMENTAL METALS

05950 BRONZE CLEANING AND REFINISHING

08710 HARDWARE

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SATIN OR RUBBED FINISH:

PART 1: GENERAL QUALITY ASSURANCE (Add)

Standards: National Association of Architectural Metals Manufacturers
Copper Alloy Finish Standards

US Finish - No. 6 Buff Satin (Natural)

Copper Development Association Finish - M 34 Hand Rubbed

PART 2: MATERIALS (Add to list)

ABRASIVE: SATIN/RUBBED FINISH (MANUAL POLISHING)

1\. 400-600 grit mineral pad, 3M Scotchbrite 7447, or equivalent

(use with toluene- acetone solvent)

2\. #0 bronze wool (use with toluene-acetone solvent)

3\. #0 pumice (use with toluene-acetone solvent)

4\. Emery (use with Turkish oil)

PART 3: EXECUTION: (Insert after repair and initial cleaning citation,
if that work is specified):

BRONZE POLISHING: SATIN OR RUBBED FINISH

1\. Manually rub the metal surface, in the direction of the grain only,
using abrasive with solvent or oil until surface is smooth and uniform
in color, and other visual characteristics.

2\. Alternatively, machine buff using successively finer abrasives,
ending with 320 grit, at a peripheral speed of 6000 ft./min., in the
direction of the grain, then hand rubbing the surface using bronze wool
and solvent or oil-based lubricant to smooth out grinding and buffing
lines.

3\. Finished bronze shall feel smooth to the touch. Directional texture
shall not be visible from a distance of 10 feet or more from the bronze
surface.

MIRROR FINISH:

PART 1: GENERAL

A. QUALITY ASSURANCE (Add)

1\. Standards: National Association of Architectural Metals
Manufacturers Copper Alloy Finish Standards

1\. US Finish - No. 8 Mirror

2\. Copper Development Association Finish - M 22, Specular

PART 2: MATERIALS (Add to list)

ABRASIVE: MIRROR FINISH (MACHINE POLISHING)

1\. Aluminum oxide

2\. Silicon carbine

PART 3: EXECUTION (Insert after repair and initial cleaning citation, if
that work is specified):

BRONZE POLISHING: MIRROR FINISH (Insert after cleaning):

1\. Polish by mechanically buffing the metal surface, in the direction
of the grain only, using cotton buff pads on an \"offset machine, held
sideways, creating a \"flapping\" action. Use aluminum oxide or silicon
carbide compounds, of successively finer grit, ending with 320 grit,
buffed at a speed of 6000 feet/min.

2\. Finish by light buffing with aluminum oxide buffing compounds using
a peripheral wheel speed of 7,000 feet/min., until directional texture
is no longer visible and surface is bright and reflective. Hand polish
edges to blend with machine polished surfaces.

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For more information about architectural metal refinishing, contact the
Regional Historic Preservation Officer, Ms. Andrea Mones O\'Hara, at
(202) 708-8173.