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Historic Preservation - Technical Procedures

Spectitle:

Removing Patina Or Tarnish From Solid Brass

Procedure code:

0501032R

Source:

Hspg Prepared For Nps - Sero

Division:

Metals

Section:

Metal Materials

Last Modified:

02/24/2012

Details:

Removing Patina Or Tarnish From Solid Brass



REMOVING PATINA OR TARNISH FROM SOLD BRASS


ALL CLEANING REMOVES SOME SURFACE METAL AND PATINA.  THEREFORE, USE
CAUTION, AS EXCESSIVE CLEANING CAN REMOVE THE TEXTURE AND FINISH OF
THE METAL.

THE CLEANING OR STRIPPING OF METALS MAY INVOLVE THE USE OF
ABRASIVES, LIQUIDS OR SOLVENTS WHICH MAY SPLASH OR RUN OFF ONTO
ADJACENT MATERIALS.  TAKE SPECIAL CARE TO PROTECT ALL ADJACENT
MATERIALS, AND DO NOT USE THIS PROCEDURE ON METALS OTHER THAN
THOSE
SPECIFIED IN THE SUMMARY.


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on removing patina or
         tarnish from solid brass.

    B.   For additional guidance relating to cleaning and
         maintaining brass, see the following procedures:

         1.   For cleaning and polishing solid brass, see 05010-10-P.

         2.   For removing old lacquer or paint from solid brass
              or brass-plate, see 05010-31-R.

         3.   For removing patina or tarnish from solid brass,
              see 05010-32-P.

         4.   For applying a protective coating to brass-plate or
              solid brass, see 05010-12-P.

    C.   Brass is an alloy of copper and zinc.  Brass-plate is a
         thin layer of brass bonded to steel.  Solid brass is more
         durable than brass-plate and, therefore, can withstand
         more rigorous methods of cleaning.  

    D.   Brass may be unfinished or lacquered.  Architectural
         brass hardware and trim is generally maintained in a
         highly polished, "bright" finish.  

         1.   Unfinished brass MUST be polished frequently in
              order to maintain its luster.  All polishing,
              however, removes some brass.

         2.   Lacquered brass will usually last about 10 years
              and does NOT require frequent polishing.

         3.   Lacquer protects the brass finish from
              deterioration, though some brilliance of its
              surface characteristics is sacrificed.  Removal and
              reapplication of the lacquer, however, will not
              harm the brass surface.

    E.   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).


PART 2---PRODUCTS

2.01 MATERIALS

    NOTE:  Chemical products are sometimes sold under a common
    name.  This usually means that the substance is not as pure as
    the same chemical sold under its chemical name.  The grade of
    purity of common name substances, however, is usually adequate
    for stain removal work, and these products should be purchased
    when available, as they tend to be less expensive.  Common
    names are indicated below by an asterisk (*).

    A.   For Removing Thin Sulfate Crusts:

         1.   Household ammonia:

              CAUTION:  DO NOT MIX AMMONIA WITH CHLORINE
              BLEACHES, A POISONOUS GAS WILL RESULT!  DO NOT USE
              BLEACH ON BIRD DROPPINGS.

              a.   Other chemical or common names include
                   Ammonium Hydroxide; Ammonia water*; Aqua
                   ammonia*.

              b.   Potential hazards:  TOXIC; MAY IRRITATE THE
                   EYES.

              c.   Available from chemical supply house, grocery
                   store or pharmaceutical supply distributor, or
                   hardware store.

         2.   Whiting:

              a.   Other chemical or common names include
                   Powdered chalk.  Kitchen flour may also be
                   substituted.

              b.   Available from paint store.

         -OR-

         1.   Orthophosphoric acid (85% concentrated):

              a.   A syrupy or deliquescent tribasic acid used
                   especially in preparing phosphates (as for
                   fertilizers), in rust-proofing metals, and as
                   a flavoring in soft drinks.

              b.   Other chemical or common names include
                   Phosphoric acid.

              c.   Potential Hazards:  CORROSIVE TO FLESH;
                   CORROSIVE TO CONCRETE, STEEL, WOOD OR GLASS.

              d.   Available from chemical supply house or
                   hardware store.

         2.   Thiourea (CS(NH2)2):

              a.   A colorless crystalline bitter compound
                   analogous to and resembling urea that is used
                   especially as a photographic and organic
                   chemical reagent.

              b.   Available from photographic supply distributor
                   (not camera shop).

         3.   Wetting agent such as "Photoflo" (Kodak), or
              approved equal.

         4.   Distilled water:  Available from supermarket or
              hardware store.

         -OR-

         1.   Citric acid:

              a.   Other chemical or common names include
                   Oxytricarballylic acid; 2-hydroxy-1,2,3-propanetricarboxylic acid.

              b.   Potential Hazards:  CORROSIVE TO CONCRETE,
                   STEEL WOOD OR GLASS; FLAMMABLE.

              c.   Available from chemical supply house,
                   drugstore or pharmaceutical supply
                   distributor, grocery store or supermarket, or
                   photographic supply distributor (not camera
                   shop).

         2.   Gum arabic

         3.   Distilled water:  Available from supermarket or
              hardware store.

         -OR-

         1.   Orthophosphoric acid (85% concentrated) (See
              Section 2.02 A.1. alternative above)

         2.   Sodium nitrate

         3.   Distilled water:  Available from supermarket or
              hardware store.

    B.   For thick sulfate crusts:

         1.   Sodium Hexametaphosphate such as "Calgon", or
              approved equal.

              -OR-

              Sulfuric Acid

         2.   Distilled water:  Available from supermarket or
              hardware store.

    C.   For pink stains:

         1.   Oxalic Acid (COOH)2 or (H2C2O4):

              a.   A poisonous strong acid that occurs in various
                   plants as oxalates and is used especially as a
                   bleaching or cleaning agent and in making
                   dyes.

              b.   Other chemical or common names include
                   Ethanedioic acid.

              c.   Potential Hazards:  TOXIC; CORROSIVE TO
                   CONCRETE, STEEL, WOOD OR GLASS.

              d.   Available from chemical supply house, dry
                   cleaning supply distributor, drugstore or
                   pharmaceutical supply distributor, hardware
                   store, or photographic supply distributor (not
                   camera shop).  (Often sold under a
                   manufacturer's brand name; the chemical name
                   may appear on the label.)

         2.   Oxalic acid cellosolve

         3.   Standard solvent (mixture of 75% Toluene, 24%
              Acetone and 1% Butyl Acetone) - (Fisher
              Scientific), or approved equal.

              a.   Toluene (C7H8):

                   1)   A liquid, aromatic hydrocarbon that
                        resembles benzene but is less volatile,
                        flammable and toxic; Is produced
                        commercially from light oils from coke-
                        oven gas and coal tar and from petroleum,
                        and is used as a solvent, in organic
                        synthesis and an antiknock agent for
                        gasoline.

                   2)   Other chemical or common names include
                        Toluol.

                   3)   Potential Hazards:  TOXIC AND FLAMMABLE.

                   4)   Available from chemical supply house,
                        hardware store, paint store or printer's
                        supply distributor.

              b.   Acetone (C3H6O):

                   1)   A volatile fragrant flammable liquid
                        ketone used chiefly as a solvent and in
                        organic synthesis and found abnormally in
                        urine.

                   2)   Other chemical or common names include
                        Dimethyl ketone; Propanone.

                   3)   Potential Hazards:  VOLATILE AND
                        FLAMMABLE SOLVENT.

                   4)   Available from chemical supply house or
                        hardware store.

         4.   Dryer-degreaser such as trichlorethylene, or
              approved equal:

              a.   Trichlorethylene (highly refined solvent):

                   CAUTION:  TRICHLOROETHYLENE IS HIGHLY TOXIC
                   AND MAY REACT WITH STRONG ALKALIS SUCH AS
                   FRESH CONCRETE TO FORM DANGEROUS GASES.

                   1)   Other chemical or common names include
                        Ethinyl trichloride.

                   2)   Potential Hazards:  TOXIC.

                   3)   Available from automotive supply
                        distributor, chemical supply house (both
                        commercial and scientific), dry cleaning
                        supply distributor, paint store,
                        photographic supply distributor (not
                        camera shop), or printer's supply
                        distributor.

    D.   Clean, potable water

    E.   Clean, soft cloths

2.03 EQUIPMENT

    A.   Eye and skin protection

    B.   Heavy gloves and protective gear

    C.   Soft natural bristle brushes


PART 3---EXECUTION

3.01 EXAMINATION

    A.   Before proceeding with steps to clean brass, examine the
         surface(s) to determine the extent of the work required.
         Look for:

         1.   Broken, cracked, missing, distorted or loose parts.

         2.   Coating failures such as chips, losses, peeling,
              cracks, bubbling and wear.

         3.   Corrosion - caused by moisture, sea water and sea
              air, deicing salts, acids, soils, gypsum plasters,
              magnesium oxychloride cements, ashes, clinkers and
              sulphur components.

3.02 PREPARATION

    A.   Protection:  

         1.   General:  Comply with recommendations of
              manufacturers of cleaners, polishes and coatings
              for protecting building surfaces against damage
              from exposure to their products.

         2.   Protect adjacent surfaces from contact with
              chemical cleaners by covering them with liquid
              strippable masking agent or polyethylene film and
              waterproof masking tape.  Apply masking agent to
              comply with manufacturer's recommendations.  Do not
              apply liquid masking agent to porous surfaces.

         3.   Protect persons and surrounding surfaces of
              building where metal surfaces are being restored,
              from damage resulting from metal cleaning and
              refinishing work.

              a.   Prevent cleaning solutions and coatings from
                   coming into contact with persons and other
                   surfaces which could be damaged by such
                   contact.

              b.   Erect temporary protection covers over
                   walkways for persons who must be in area of
                   operations during course of metal cleaning and
                   refinishing work.

              c.   Provide ventilation to eliminate the spread of
                   fumes to unaffected spaces.

    B.   Surface Preparation:  

         1.   Before cleaning, determine if your brass surface is
              solid or plated:  

              a.   A magnet will stick to the steel beneath brass
                   plating; it will not stick to solid brass.  

              b.   Solid brass can withstand much harsher
                   treatment than brass plating can.  

3.03 ERECTION, INSTALLATION, APPLICATION

    NOTE:  WHEN CLEANING, TRY TO RETAIN THE BRASS PATINA, AS THIS
    PROTECTS THE BRASS FROM FURTHER CORROSION.  
   
    A.   For thin sulfate crusts:

         1.   Mix whiting and ammonia.

              -OR-

              Mix 8 ml of 85%  concentrated orthophosphoric acid,
              7 g thiourea, 0.2 ml wetting agent, and enough
              water to make 100 ml.

              -OR-

              Mix 5 g citric acid, 1 g gum arabic, enough
              distilled water to make 100 ml.

              -OR-

              Mix 6 ml of 85% orthophosphoric acid, 2 g sodium
              nitrate, and enough distilled water to make 100 ml.

         2.   Apply mixture and rub over the brass surface using
              a clean, soft cloth.

         3.   Thoroughly rinse the surface with clean, clear
              water and wipe dry with a clean, soft cloth to
              prevent water spotting.

    B.   For thick sulfate crusts:

         1.   Mix 5 g to 15 g of sodium hexametaphosphate with
              enough distilled water to make 100 ml.

              -OR-

              Mix 10 ml of concentrated sulfuric acid with enough
              distilled water to make 100 ml.  Stir the acid into
              the water slowly.

              NOTE:  THE SULFURIC ACID SOLUTION SHOULD BE
              PREPARED AND USED BY PERSONS TRAINED IN HANDLING
              DANGEROUS ACIDS.

              CAUTION:  ALWAYS ADD ACID TO WATER.  NEVER THE
              REVERSE.

         2.   Apply mixture to the brass surface with a clean,
              soft cloth.

         3.   Brush off loosened crust material.

         4.   Thoroughly rinse the surface with clean, clear
              water and wipe dry with a clean, soft cloth to
              prevent water spotting.

    C.   For pink stains (metals suffering from dezincification):

         1.   Dissolve 5% oxalic acid in a mixture of 3 parts
              water and 1 part oxalic acid cellosolve.

         2.   Swab the affected area with the solution.

         3.   Rinse the surface with a standard solvent to remove
              any cleaner residue.

         4.   Wipe the surface with a dryer-greaser using a
              clean, soft cloth and allow to dry.

         5.   Repeat the process as required to remove the pink
              stains.

              NOTE:  CLEAR COATING MUST BE APPLIED TO METAL
              SURFACE WITHIN 4 HOURS OF CLEANING.

         6.   Thoroughly rinse the surface with clean, clear
              water and wipe dry with a clean, soft cloth to
              prevent water spotting.

    D.   Polish the brass with a brass cleaner.  See 05010-03-P
         and 05010-10-P for guidance.

3.04 ADJUSTING/CLEANING

    A.   During the work, remove from the site discarded cleaning
         and coating materials, rubbish, cans and rags at end of
         each work day.

    B.   Upon completion of coating work, remove all protective
         coverings and coatings, and clean window glass and other
         coating-spattered surfaces.  Remove spattered coatings by
         proper methods as recommended by coating manufacturer,
         using care not to damage adjacent surfaces.

                         END OF SECTION