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Historic Preservation - Technical Procedures

Spectitle:

Removing Copper Sulfate From Bronze Features

Procedure code:

0501023R

Source:

National Capitol Region Specifications

Division:

Metals

Section:

Metal Materials

Last Modified:

02/24/2012

Details:

Removing Copper Sulfate From Bronze Features



REMOVING COPPER SULFATE FROM BRONZE FEATURES


PART 1---GENERAL

1.01 SUMMARY

    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

         3.   Submittals

         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.

PART 2---PRODUCTS

2.01 MANUFACTURERS

    A.   Industrial Soap Co.
         2930 Market Street
         St. Louis, Missouri 63103

2.02 MATERIALS

    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
         equal.

    D.   Water shall be clean, potable, non-staining and free of
         materials detrimental to all surfaces to be cleaned.
   
    E.   Cloth: Clean, cotton waste.
   
2.03 EQUIPMENT

    A.   Stiff bristle brushes

    B.   Wide tip nozzle

    C.   Oxidizing agent: Aluminum chloride or liquid sulphur


PART 3---EXECUTION

3.01 PREPARATION

    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
         sample panels.

         1.   Method "A":
         
              a.   Wash with non-ionic detergent scrubbing the
                   stained areas with a stiff natural bristle
                   brush.  

              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
                   2.5 feet.
             
              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
                   above.
             
              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