Patination Formulas For Bronze

Procedure code:
503002G
Source:
Outdoor Sculpture Manual
Division:
Metals
Section:
Metal Coatings
Last Modified:
08/02/2016

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.
Last Reviewed 2016-08-02