Removing Patina or Tarnish from Solid Brass

Procedure code:
501032S
Source:
Hspg Prepared For Nps - Sero
Division:
Metals
Section:
Metal Materials
Last Modified:
08/16/2016

PREFACE: 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

  1. This procedure includes guidance on removing patina or tarnish from solid brass.
  2. For additional guidance relating to cleaning and maintaining brass, see the following procedures:
    1. For cleaning and polishing solid brass, see "Cleaning and Polishing Solid Brass".
    2. For removing old lacquer or paint from solid brass or brass-plate, see "Removing Old Lacquer Or Paint From Solid Brass Or Brass-Plate".
    3. For removing patina or tarnish from solid brass, see "Removing Patina Or Tarnish From Solid Brass".
    4. For applying a protective coating to brass-plate or solid brass, see "Classifications Of Aluminum Cleaners".
  3. 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.  
  4. 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.
  5. See "General Project Guidelines" 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 (*).

  1. 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.
      1. Other chemical or common names include Ammonium Hydroxide; Ammonia water*; Aqua ammonia*.
      2. Potential hazards:  TOXIC; MAY IRRITATE THE EYES.
      3. Available from chemical supply house, grocery store or pharmaceutical supply distributor, or hardware store.
    2. Whiting:
      1. Other chemical or common names include Powdered chalk.  Kitchen flour may also be substituted.
      2. Available from paint store.
         -OR-
    3. Orthophosphoric acid (85% concentrated):
      1. 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.
      2. Other chemical or common names include Phosphoric acid.
      3. Potential Hazards: CAUSTIC TO FLESH; CORROSIVE TO CONCRETE, STEEL, WOOD OR GLASS. Available from chemical supply house or hardware store.
    4. Thiourea (CS(NH2)2):
      1. A colorless crystalline bitter compound analogous to and resembling urea that is used especially as a photographic and organic chemical reagent.
      2. Available from photographic supply distributor (not camera shop).
    5. Wetting agent such as "Photoflo" (Kodak), or approved equal.
    6. Distilled water:  Available from supermarket or hardware store.
      -OR-
    7. Citric acid:
      1. Other chemical or common names include Oxytricarballylic acid; 2-hydroxy-1,2,3-propanetricarboxylic acid.
      2. Potential Hazards:  CORROSIVE TO CONCRETE, STEEL WOOD OR GLASS; FLAMMABLE.
      3. Available from chemical supply house, drugstore or pharmaceutical supply distributor, grocery store or supermarket, or photographic supply distributor (not camera shop).
    8. Gum Arabic
    9. Distilled water:  Available from supermarket or hardware store.
      -OR-
    10. Orthophosphoric acid (85% concentrated) (See Section 2.02 A.1. alternative above)
    11. Sodium nitrate
    12. Distilled water:  Available from supermarket or hardware store.
  2. For thick sulfate crusts:
    1. Sodium Hexametaphosphate such as "Calgon", or approved equal.
       -OR-
    2. Sulfuric Acid
    3. Distilled water:  Available from supermarket or hardware store.
  3. For pink stains:
    1. Oxalic Acid (COOH)2 or (H2C2O4):
      1. 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.
      2. Other chemical or common names include Ethanedioic acid.
      3. Potential Hazards:  TOXIC; CORROSIVE TO CONCRETE, STEEL, WOOD OR GLASS.
      4. 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.
      1. 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.
      2. 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:
      1. 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.
  4. Clean, potable water
  5. Clean, soft cloths

2.03 EQUIPMENT

  1. Eye and skin protection
  2. Heavy gloves and protective gear
  3. Soft natural bristle brushes

PART 3---EXECUTION

3.01 EXAMINATION

  1. 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

  1. 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.
      1. Prevent cleaning solutions and coatings from coming into contact with persons and other surfaces which could be damaged by such contact.
      2. Erect temporary protection covers over walkways for persons who must be in area of operations during course of metal cleaning and refinishing work.
      3. Provide ventilation to eliminate the spread of fumes to unaffected spaces.
  2. Surface Preparation:  
    1. Before cleaning, determine if your brass surface is solid or plated:  
      1. A magnet will stick to the steel beneath brass plating; it will not stick to solid brass.  
      2. 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.  

  1. For thin sulfate crusts:
    1. Mix whiting and ammonia.
      -OR-
    2. Mix 8 ml of 85%  concentrated orthophosphoric acid, 7 g thiourea, 0.2 ml wetting agent, and enough water to make 100 ml.
      -OR-
    3. Mix 5 g citric acid, 1 g gum arabic, enough distilled water to make 100 ml.
      -OR-
    4. Mix 6 ml of 85% orthophosphoric acid, 2 g sodium nitrate, and enough distilled water to make 100 ml.
    5. Apply mixture and rub over the brass surface using a clean, soft cloth.
    6. Thoroughly rinse the surface with clean, clear water and wipe dry with a clean, soft cloth to prevent water spotting.
  2. For thick sulfate crusts:
    1. Mix 5 g to 15 g of sodium hexametaphosphate with enough distilled water to make 100 ml.
      -OR-
    2. 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.
    3. Apply mixture to the brass surface with a clean, soft cloth.
    4. Brush off loosened crust material.
    5. Thoroughly rinse the surface with clean, clear water and wipe dry with a clean, soft cloth to prevent water spotting.
  3. 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.
  4. Polish the brass with a brass cleaner.  See "Cleaning and Polishing Brass-Plate" and "Cleaning and Polishing Solid Brass" for guidance.

3.04 ADJUSTING/CLEANING

  1. During the work, remove from the site discarded cleaning and coating materials, rubbish, cans and rags at end ofeach work day.
  2. 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

Last Reviewed 2016-08-16