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Historic Preservation - Technical Procedures

Spectitle:
Patination Formulas For Bronze

Procedure code:
0503002S

Source:
Outdoor Sculpture Manual

Division:
Metals

Section:
Metal Coatings

Last Modified:
02/24/2012

Details:
Patination Formulas For Bronze



PATINATION FORMULAS FOR BRONZE


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 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 turn
green.  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.

                         END OF SECTION