Patination Formulas For Bronze

Technical Procedures Disclaimer

Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.

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We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.

This standard includes formulas for patinizing bronze to achieve a specific color. It is intended as a reference only, for validating project and/or vendor recommendations and specifications. Formulas are listed below and designated by color.

For Raw 85-5-5-5

(semi-transparent finish; nitric acid pickle process):

  • Nitric Acid (diluted)

For Basic Green

(Semi-transparent finish; Hot process):

  • Copper Nitrate (1 tsp.)
  • Clean, potable water (1 pint)

Note: A fresh mixture is needed for each coloring.

For Antique Green

(Opaque finish; Cold process):

  • Cupric Nitrate (40 grams)
  • Ammonium Chloride (40 grams)
  • Calcium Chloride (40 grams)
  • Clean, potable water (enough to make 1 liter)

Note: Frog green results after several applications, 1/2 hour intervals, color is not satisfactory alone.

For Yellow Green

(Heavy opaque finish; Cold process):

  • Ammonium Chloride (7 parts/weight)
  • Copper Acetate (4 parts/weight)
  • Clean, potable water (8 parts/weight)

Note: Takes effect after several applications.

For Light Green

(Opaque finish; Cold process):

  • Ammonium Chloride (16 parts)
  • Sodium Chloride (16 parts)
  • Ammonium Hydroxide (16 parts)

Note: Twelve hour Intervals for several days, for deeper green, add 16 parts of copper sulfate.

For Blue Green

(Heavy opaque finish; Cold process):

  • Vinegar

Note: Bury object in sawdust saturated with vinegar for several days, sprinkle more if needed.

For Wine Vinegar Green

(Opaque finish; Cold process):

  • Red or White Wine Vinegar (1/2 liter)
  • Ammonium Hydroxide (1 tbsp.)
  • Muriatic Acid (1 tbsp.)
  • Sodium Chloride - salt (1 tsp.)
  • Ammonium Chloride (100 grams)
  • Clean, potable water

Note: Apply solution for several days at 12 hour intervals.

For Apple Green

(Heavy opaque finish; Cold process):

  • Sodium Chloride (5 parts/weight)
  • Ammonia (4 parts/weight)
  • Ammonium Chloride (5 parts/weight)
  • Glacial Acid (4 parts/weight)
  • Clean, potable water (32 parts/weight)

For Green Russet Bronze

(Cold process):

  • Sodium Thiosulfate (8 ounces)
  • Nitric Acid (0.25 fluid ounces)
  • Clean, potable water (1 gallon)

Note: Normally applied to brass objects

For Green From Brown Patina:

(Cold process)

  • Liver of Sulfur (1 large lump crushed)
  • Clean, potable water (1 pint)
  • Note: Silica bronze only!

-OR-

  • Cupric Nitrate (1 tbsp.)
  • Clean potable water (1 pint)

For Brown:

  • (Cold process)

    • Sodium Thiosulfate (1 part/weight)
    • Ferric Nitrate (8 parts/weight)
    • Clean, potable water (128 parts/weight)
      -OR-
  • (Vat dipping process)

    • Cubric Sulfate (4 ounces)
    • Potassium Chlorate (2 ounces)
    • Clean, potable water (1 gallon)
      Note: Immerse for a minute or so, then immerse in a solution made of 1 ounce liquid sulfur to 1 gallon water. Rinse in how water. Scratch-brush dry with sawdust.
      -OR-
  • (Cold process)

    • Ammonium Carbonate (3 parts)
    • Cupric Acetate (1 part)
    • Tartaric Acid in Vinegar (1 part)
    • Sodium Chloride Salt (1 part)
      Note: Make a paste of these ingredients, smooth it over the bronze
      for 1 hour and rinse with hot water.

-OR-

  • (Vat solution process)

    • Ammonium Chloride (4 parts)
    • Potassium Oxalate (1 part)
    • Acetic Acid (200 parts)
      Note: Heat solution, then dip for 4 to 5 minutes. Dry and repeat
      until desired color is achieved.

For Light To Dark Brown:

  • (Transparent finish; Hot process)

    • Ferric Nitrate (1/2 tsp.)
    • Clean, potable water (1 pint)
    • Note: A fresh mixture is needed for each coloring.
      -OR-
  • (Semi-opaque to opaque finish; Hot or cold process)

    • Liver of Sulfur (1 large lump crushed)
    • Clean, potable water (1 pint)

For matte brown

(Opaque finish; Cold process):

  • Barium Sulfide (1 ounce)
  • Potassium Sulfide (1/4 ounce)
  • Ammonia (2 ounces)
  • Clean, potable water (3-5 quarts)
    Note: Darkens immediately after applications, matte color is best without a preservative.

For Japanese Brown

(Transparent finish; Cold dip process - dip or brush):

  • Copper Sulfate (5 ounces)
  • Cupric Acetate (5 ounces)
  • Copper Carbonate (5 ounces)
  • Clean, potable water (1 gallon)

Note: Works well on 85/3/5 bronze, but will turn black on silica bronze.

For Golden Brown To Red Brown

(Transparent and opaque finish; Cold process):

  • Ferric Nitrate (1 tsp.)
  • Clean, potable water (1 pint)
    Note: For transparent finish, use and air gun; For opaque finish,
    use a stippling brush.

For Orange-Brown

(Hot process):

  • Liver of Sulfur (1 large lump crushed)
  • Clean, potable water (1 pint)
    Note: Heat bronze.
    -OR-
  • Cupric Nitrate (1 tbsp.)
  • Clean, potable water (1 pint)
    -OR-
  • Cupric Chloride (3 ounces)
  • Ammonium Chloride (1/2 ounce)
  • Clean, potable water (1 pint)

For Orange Brown to Rust Brown:

(Semi-opaque to opaque finish; Hot or cold process

    • Ferric Nitrate (1 tbsp.)
    • Ferric Perchloride (1 tbsp.)
    • Clean, potable water (1 pint)
      Note: Combined cold w/cupric nitrate (allow 2 to 3 hours for results).
      -OR-
  • (Opaque finish; Hot process)

    • Ferric Nitrate (1 tbsp.)
    • Cupric Nitrate (1 tbsp.)
    • Clean, potable water (1 pint)
      Note: Stipple with a brush. Many coats may be required. Will appear slightly dark, yet more transparent.
      -OR-
  • (Semi-opaque finish; Hot process)

    • Ferric Nitrate (1 tsp.)
    • Ferric Oxide (1 tsp.)
    • Clean, potable water (1 pint)
      Note: Deeper rust brown in low areas.
      -OR-
    • Golden Antimony Sulfide (1 tbsp.)
    • Caustic Soda - lye (2 ounces)
      Note: At boiling temperature, repeat brush process if not dark
      enough.

For Rust Brown:

  • Ferric Nitrate (3 ounces)
  • Perchloride of Iron (2 ounces)
  • Clean, potable water (1-3 quarts)
    Note: Takes immediate effect.

For Red/Brown (Hot process):

  • Cupric Sulfide (40 grams)
  • Liver of Sulfur (40 grams)
  • Ferric Oxide (10 grams)
  • Clean, potable water (4 liters)
    Note: If just cupric sulfide and liver of sulfur are used, a blue-black will occur.

For Dark Red, Brown:

  • (Hot process)

    • Cupric Sulfide (1 tsp.)
    • Liver of Sulfure (1 tsp.)
    • Clean, potable water (1 pint)
      -OR-
  • (Hot process - 140 F)

    • Nickel Sulfate (1/2 ounce)
    • Cupric Sulfate (1/2 ounce)
    • Potassium Chlorate (1/2 ounce)
    • Clean, potable water (1 gallon)
      Note: Apply with a moderate wet scratch brush to even out color. Works better on 85/3/5 bronze than everdur. Wax improves the color greatly.
      -OR-
  • (Cold process)

    • Sodium Thiosulfate (1 part/weight)
    • Ferric Nitrate (1 part)
    • Clean, potable water (128 parts)
      Note: Works well on everdur.

For Purple-Brown (Hot process):

  • Cupric nitrate (1 tbsp.)
  • Saturated potassium Ferrocyanide (coat)

For Basic Brown to Black

(Transparent finish; Hot or cold process):

  • Potassium Sulfide (1 grape size lump)
  • Clean, potable water (1 pint)
    Note: Solution becomes neutral after the first application.

For Brown To Black

(Semi-opaque finish; Hot or cold process):

  • Antimony Sulfide (2 parts/weight)
  • Sodium Hydroxide or Caustic Soda - lye (4 parts/weight)
  • Clean, potable water (256 parts/weight)
    Note: Works well on 85/3/5 bronze but turns black on silica bronze.

For Chestnut To Dark Brown To Black

(Hot process):

  • Ferric Nitrate (1 cup)
  • Motor Oil
  • Clean, potable water (1 pint)
    Note: Apply nitrate solution to hot bronze, then 1 coat of motor oil. Heat until chestnut brown. 3 coats will be darker. Cool in water or air and apply wax to alleviate stickiness.

For Brown To Black On Silica/Golden Yellow To Orange On 85/3/5

(Hot process or VAT solution):

  • Sodium Thiosulfate (1/2 ounce)
  • Ferric Nitrate (2 ounces)
  • Clean, potable water (1 quart)
    Note: Toxic mixture, use in a sell ventilated place. Either heat the bronze or dip in the mixture heated to the boiling point.

For Blue

(Transparent Finish; Cold Dip Process):

  • Sodium Thiosulfate (60 grams)
  • Nitric Acid (4 grams)
  • Clean, potable water (1 quart)

For Peacock Blue

(Transparent finish; Cold dip process):

  • Sodium Thiosulfate (150 grams/liter)
  • Lead Acetate (25 grams)
  • Cream of Tartar (30 grams)
  • Clean, potable water (1 liter)
    Note: Immerse object for 20-30 minutes, preservative should be
    applied immediately after solution has dried.

For Basic Blue-Black

(Transparent finish; Hot or cold process):

  • Ammonium Sulfide (1 tsp.)
  • Clean, potable water (1 pint)

For Metallic Blue-Black (Cold Dip process):

  • Yellow Barium Sulfide (1 part/weight)
  • Clean, potable water (128 parts/weight)
    Note: Immerse overnight.

For Purple (Transparent finish; Hot process):

  • Copper Nitrate (1 tsp.)
  • Clean, potable water (1 pint)
  • Potassium Ferrocyanide

For Despiau Black (Hot process):

  • Solution 1:

    • Copper Nitrate (1 tsp.)
    • Clean, potable water (1 pint)
  • Solution 2:

    • Ferric Nitrate (1/2 tsp.)
    • Clean, potable water (1 pint)
  • Solution 3:

    • Ammonium Sulfide (1/2 tsp.)
    • Ferric Nitrate (1/2 tsp.)
    • Clean, potable water (1/2 pint)
  • Solution 4:

    • Potassium Sulfate (1/2 tsp.)
    • Ferric Nitrate (1/2 tsp.)
    • Clean, potable water (1/2 pint)
      Note: Form a base patina with Solution #1, then add a light coat of Solution #2, then apply Solution #3, then water, then Solution #4, then water, then Solution #3...until desired intensity is achieved.

For Transparent Black

(Transparent finish; Cold process):

  • Chlormoauric Acid Crystal or Cold Chloride (1/2 gram)
  • Clean, potable water (100 milliliters)
    Note: Paint or spray (with a glass atomizer) one coat; can also be
    used as a dip.

For White

(Opaque finish; Cold process):

  • Gesso (diluted liquid)
  • Powdered colors
    Note: Paint gesso to the surface, a light spray of acrylic can be
    used on patches of exposed bronze.

For Antique White

(Semi-opaque finish; Hot process):

  • Bismuth Nitrate (2 tsp.)
  • Potassium Sulfide (1 pinch)
  • Clean, potable water (1 pint)
    Note: Slightly oxidize object with torch, ferric or copper nitrate
    may be substituted.

For Straw Yellow

(Transparent finish; Hot process):

  • Ferric Nitrate - homemade grounds (1/2 tsp.)
  • Clean, potable water (1/2 pint)
    Note: Pour nitric acid over a pint jar of rusty nails until 1/4
    full, perform outdoors, mixture betters with age but can only be
    used once.

For Nickel Pate

(Opaque finish; Hot process - 110-140 degrees F):

  • Nickel Sulfate (24 ounces)
  • Ammonium Chloride (3.3 ounces)
  • Boric Acid (4 ounces)
  • Clean, potable water (1 gallon)
    Note: 25-50 amps/sq. ft. varied effects by blocking out areas with
    lacquer.

For Chromium Plate

(Opaque finish; Hot process - 120 F):

  • Chromium Acid (53 ounces)
  • Sulfate (.053 ounces)
  • Clean, potable water (1 gallon)
    Note: 200 amps/sq. ft., same characteristic as the nickel plate formula.

For Verde

(Cold dip process):

  • Copper Sulfate (8 parts/weight)
  • Ammonium Chloride (4 parts/weight)
  • Sodium Chloride (4 parts/weight)
  • Zinc Chloride (1 part/weight)
  • Glacial Acetic Acid (3 parts/weight)
  • Clean, potable water (128 parts/weight)
    Note: Immerse for a few minutes, then remove and repeat until
    color appears.

For Light Olive

(Cold process):

  • Copper Chloride (8 ounces)
  • Ferric Chloride (8 ounces)
  • Clean, potable water (1 gallon)
    Note: Normally applied to brass objects.

For Olive Antique

(Cold process):

  • Potassium Polysulfide (0.33 ounces)
  • Methyl Orange Indic Soln (5 milliliters)
  • Clean, potable water (1 gallon)
    -OR-
  • Ferric Nitrate (8 ounces)
  • Sodium Thiosulfate (2 ounces)
  • Clean, potable water (1 gallon)
    Note: Normally applied to brass objects.

For Verde Antique

(Cold process):

  • Sodium Dichromate (12 ounces)
  • Copper Sulfate (4 ounces)
    Note: Normally applied to brass objects.

For Color That Varies

(Hot or cold process):

  • Cupric Chloride (3 ounces)
  • Ammonium Chloride (1/2 ounce)
  • Clean, potable water (1 pint)
    Note: Works well on everdur. If put on cold, patina will turngreen. If put under hot tap water, will turn orange-brown. If put on hot over an ammonium sulfide or liver of sulfur patina first and cupric nitrate second, the bronze will turn orange to brown.

References:

  • Kipper, Patinas for Silicon Bronze, 1995.
  • Hughes and Rowe, The Coloring, Bronzing and Patination of Metals, 1991.