Removing Copper Sulfate From Bronze Features
- Procedure code:
- National Capitol Region Specifications
- Metal Materials
- Last Modified:
REMOVING COPPER SULFATE FROM BRONZE FEATURES
A. This procedure includes guidance on removing copper
sulfate deposits from bronze features. Two methods are
described under Part 3.
B. See 01100-07-S for general project guidelines to be
reviewed along with this procedure. These guidelines
cover the following sections:
1. Safety Precautions
2. Historic Structures Precautions
4. Quality Assurance
5. Delivery, Storage and Handling
6. Project/Site Conditions
7. Sequencing and Scheduling
8. General Protection (Surface and Surrounding)
These guidelines should be reviewed prior to performing
this procedure and should be followed, when applicable,
along with recommendations from the Regional Historic
Preservation Officer (RHPO).
C. Cleaning and refinishing bronze is highly specialized and
should be conducted under the supervision of a metals
conservator. All chemicals and cleaning methods should
be approved prior to use by the metals conservator to
ensure protection of historic metals.
A. Industrial Soap Co.
B. 3M Consumer Products Group
A. Non-ionic Detergent: A controlled suds, silicate
buffered, non-ionic, rinseless-type synthetic detergent,
containing no soap, alkali, solvents, abrasives, acids or
caustics such as "Zyfo" cleaner concentrate (Industrial
Soap Co.), or approved equal.
B. Solvent: 75% toluene + 24% acetone + 19% butal acetate.
C. Abrasive: Abrasive shall be silicon carbide abrasive
pads such as "Scotch-Brite" (3M Company), or approved
D. Water shall be clean, potable, non-staining and free of
materials detrimental to all surfaces to be cleaned.
E. Cloth: Clean, cotton waste.
A. Stiff bristle brushes
B. Wide tip nozzle
C. Oxidizing agent: Aluminum chloride or liquid sulphur
A. Protection: All exterior stone that may come in contact
with the cleaner shall be rinsed before, during and after
cleaning in order to avoid staining the stone.
3.01 ERECTION, INSTALLATION, APPLICATION
A. If the copper sulfate formation has not advanced too far
(light streaking), remove the sulfate layer and expose
the original patina. Select gentlest method - "A" or "B"
which satisfactorily removes sulfate as determined by
1. Method "A":
a. Wash with non-ionic detergent scrubbing the
stained areas with a stiff natural bristle
b. Rinse with cold water to remove all traces of
detergent and residue. Rinse water pressure
shall not exceed 100 psi and shall be sprayed
through nozzles fitted with 15-20 degree wide
tips. Nozzles shall be held perpendicular to
the surface at a working distance of 1.5 to
c. Apply clear protective coating. See 05010-08-
P for guidance.
2. Method "B":
a. Wash with solvent and abrasive pad. Avoid
abrading existing patina finish.
b. Rinse with cold water as specified in 1b
c. Dry with clean, soft cloth.
d. Apply clear protective coating. See 05010-08-
P for guidance.
B. When the finish cannot be restored by removal of sulfate
formation, chemically strip to bare metal and repatinate.
See 05010-24-R for guidance.
END OF SECTION