Artificial patination is the process of inducing a patina layer on metal surfaces through the application of chemical compounds. Unlike natural patination that occurs over time, artificial patination accelerates the patina formation to achieve aesthetic effects and protection. When done correctly, artificial patination can give metal surfaces beautiful and distinctive finishes resembling naturally aged patinas.
Copper Patination Compounds
Copper and its alloys such as bronze and brass are commonly patinated to produce blue, green, brown, and black finishes. This is achieved by using compounds that react with the copper metal to form patina layers consisting of copper carbonates, oxides, sulfides, or chlorides.
Copper Sulfate
Copper sulfate is one of the most popular patinating agents for achieving blue and green patinas on copper, bronze and brass. When copper sulfate reacts with the copper metal surface, it forms copper carbonate and copper chloride compounds.
The blue-green patina color results from a mixture of the blue copper carbonate, green copper chloride, and unreacted copper metal. Copper sulfate is available as pentahydrate crystals which are dissolved in warm water before application.
Procedure:
- Clean and degrease the copper surface
- Make a saturated copper sulfate solution
- Apply solution by brushing or immersion
- Let it react for 5-60 minutes depending on depth of patina desired
- Rinse and neutralize with baking soda and water
- Apply wax or varnish to stabilize patina
Safety Tips:
- Use gloves when handling copper sulfate crystals
- Work in a well-ventilated area
- Avoid ingestion or contact with eyes and skin
Patina Colors:
- Blue-green, turquoise
- Can turn brownish in high humidity environments
Copper Nitrate
Similar to copper sulfate, copper nitrate also reacts with copper metal to form copper carbonate and copper chloride compounds. It produces blue, greenish, or black patina finishes on copper alloys.
The patina colors can range from a soft pale blue to dark blackish-green depending on concentration and application method. Copper nitrate is available as crystals which are dissolved in distilled water to make the patinating solution.
Procedure:
- Clean and polish the copper surface
- Make copper nitrate solution of desired concentration
- Swab or immerse surface in solution for a few seconds to minutes
- Rinse and wash with baking soda water
- Apply wax or varnish to protect patina
Safety Tips:
- Use gloves, mask, and eye protection
- Work in a well-ventilated area
- Avoid ingestion or contact with skin and eyes
Patina Colors:
- Blue, greenish-blue, pale green, dark greenish-black
Iron and Steel Patination Compounds
Iron and steel surfaces can be patinated to produce brown, black, or reddish finishes using iron oxide forming compounds. This protects the metal from corrosion and makes the surface more aesthetically pleasing.
Ferric Nitrate
Ferric nitrate reacts with iron or steel surfaces to form iron oxide layers. This results in yellowish, brown, or black patina finishes depending on concentration and application method.
Procedure:
- Clean and degrease the metal surface
- Make a ferric nitrate solution in distilled water
- Swab or brush solution onto surface
- Let it react for 5-60 minutes
- Rinse and dry
Safety Tips:
- Use gloves, mask, and eye protection
- Avoid ingestion or contact with skin and eyes
Patina Colors:
- Yellowish-brown to black finishes
Ferric Chloride
Ferric chloride is also used to patinate iron and steel to form adherent iron oxide layers. It produces brownish-red, chocolate brown, or black patina colors.
Procedure:
- Clean and degrease the metal surface
- Make a ferric chloride solution in distilled water
- Apply solution by brushing or immersion
- Let react for 5-60 minutes depending on desired patina depth
- Rinse and dry thoroughly
Safety Tips:
- Use gloves, mask, and eye protection
- Work in a well-ventilated area
- Avoid ingestion or contact with skin and eyes
Patina Colors:
- Reddish-brown, chocolate browns, black
Sulfur-Based Patination Compounds
Sulfur-containing compounds are commonly used to patinate copper alloys by forming copper sulfide layers. This produces black, brown, or bluish-grey patinas.
Ammonium Sulfide
Ammonium sulfide reacts with copper alloys to form copper sulfide patinas in shades of black, grey-brown, or indigo blue.
Procedure:
- Clean and degrease the metal surface
- Make an ammonium sulfide solution in distilled water
- Swab or immerse the metal in the solution
- Let react for 5 seconds to 5 minutes
- Rinse and dry
- Apply wax or varnish to stabilize patina
Safety Tips:
- Work in a well-ventilated area
- Avoid ingestion or contact with eyes and skin
Patina Colors:
- Black, charcoal grey, brownish-grey, indigo blue
Potassium Sulfide (Liver of Sulfur)
Potassium sulfide is also known as liver of sulfur in patination processes. It reacts with copper alloys to produce black, brown, or bluish-grey patinas consisting of copper sulfide compounds.
Procedure:
- Clean and degrease the metal surface
- Make a liver of sulfur solution in distilled water
- Apply solution by brushing or immersion
- Let react for 5 seconds to 5 minutes
- Rinse and dry
- Apply wax or varnish to protect patina
Safety Tips:
- Work in a well-ventilated area
- Avoid ingestion or contact with eyes and skin
Patina Colors:
- Black, chocolate browns, charcoal greys, blues
Chloride-Based Patination Compounds
Chloride compounds like sodium chloride and ammonium chloride are used to produce patinas on copper alloys by forming copper chloride compounds. This gives blue, green, or grey patina finishes.
Sodium Chloride (Salt)
Common table salt or sodium chloride can be used to patinate copper alloys by forming copper chloride layers. This produces green or greyish patinas.
Procedure:
- Clean and degrease the metal surface
- Make a saturated salt solution in hot water
- Apply solution by brushing or immersion
- Let react for 5-60 minutes
- Rinse and dry
Safety Tips:
- Avoid ingestion or contact with eyes
Patina Colors:
- Greyish-green or light greenish patinas
Ammonium Chloride
Ammonium chloride reacts with copper surfaces to form adherent patinas consisting of copper chloride compounds. This gives blue, greenish, or grey patina finishes.
Procedure:
- Clean and degrease the metal surface
- Make an ammonium chloride solution in distilled water
- Apply solution by brushing, immersion or fuming
- Let react for a few minutes to an hour
- Rinse and dry
- Apply wax or varnish
Safety Tips:
- Avoid ingestion or contact with eyes and skin
- Work in a well-ventilated area
Patina Colors:
- Greyish-blue, sea green, pale greenish patinas
Acid Solutions for Patination
Dilute acid solutions are sometimes used to etch and patinate metal surfaces. This produces unique mottled, etched finishes.
Vinegar or Acetic Acid
Vinegar contains acetic acid which can be used to patinate copper alloys by forming verdigris (copper acetates). It produces blue, green, or grey patinas depending on metal composition and time of exposure.
Procedure:
- Clean and degrease the metal surface
- Apply or immerse in undiluted white vinegar
- Let react for 5 minutes to 24 hours
- Rinse and dry
- Apply wax or varnish
Safety Tips:
- Use gloves, mask, and eye protection
- Avoid ingestion or contact with eyes and skin
Patina Colors:
- Blue-green, grey-green, pale green patinas
Applying and Protecting Patinas
Proper surface preparation, application method, and patina protection are key to achieving quality, long-lasting patina finishes on metal surfaces.
Surface Preparation
Meticulous cleaning and degreasing of the metal surface is vital before patination. All oils, dirt, corrosion deposits, waxes, and lacquers must be removed for the patinating compounds to react evenly with the bare metal.
Application Methods
Patinating solutions can be applied by immersion, brushing, or swabbing using cotton balls, sponges, or rags. Fuming with ammonium chloride produces unique mottled patinas. Experimentation may be required to find the right application method for each patinating agent.
Protecting Patinas
Unprotected patinas are ephemeral and will wear off quickly with handling. Multiple thin coats of wax, lacquer, or varnish are recommended to stabilize and protect patina finishes for lasting durability and aesthetics.
Safety Precautions
Most patinating chemicals are hazardous and can cause severe injury if handled improperly. Observe the following safety measures:
- Wear gloves, mask, goggles/face shield at all times
- Work in a well-ventilated area
- Avoid ingestion, skin, and eye contact
- Label solutions clearly and store safely
- Follow manufacturer safety instructions
- Dispose waste properly
With responsible use, patinating chemicals offer a safe way to create beautiful patinas on metal that protect and enhance the aesthetic appeal of metal art and artifacts.
Final Thoughts
The variety of colors and textures possible are virtually endless with the use of these common patinating compounds on different metal alloys. Mastering patination techniques takes experimentation but offers satisfying ways for metalsmiths and artists to leave their permanent mark on metal surfaces.