How to Color Metal Art

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Coloring metal art.
Coloring metal art. (Image: metal image by Katarzyna Szura from Fotolia.com)

When creating metal sculptures, adding color can bring new dimensions to your work, while adding some energy and vibrancy to a piece. There are many ways to color metals, from painting to anodizing, and the technique you choose will depend on the kind of metal, the size of the piece and the overall effect you wish to create.

Things You'll Need

  • Metal artwork (steel, copper, aluminum or bronze)
  • Metal primer
  • Spray paint
  • Acrylic paint
  • Commercial spray cleaner
  • Masking tape
  • Drop cloth
  • Rubber gloves
  • Gun bluing solution
  • Multi-purpose mechanic's oil
  • Steel wool
  • Sand paper
  • Household ammonia
  • Salt
  • Sulfuric Acid
  • 2 plastic buckets
  • 12-volt AC power supply
  • Fabric dye
  • Washing soda
  • Distilled water
  • Plastic spray bottle
  • Boiled linseed oil

Painting Metal

For large areas of color, select a spray paint in the shade you wish to use and a spray-on primer rated for use with metal.

Find a well-ventilated area and lay down a drop cloth. Put on a smock or apron and a pair of rubber or latex gloves.

Clean the surface of the metal with a commercial cleaner to remove grease, dirt and other debris that may prevent the adhesion of the paint. You also may lightly sand the surface of the metal to remove any rust or oxidation clinging to the surface.

Cover with masking tape any surfaces you do not wish to color. Following the instructions on your can of primer, cover the entire piece in smooth, even coat and allow it to dry completely.

Follow the instructions on your can of spray paint and apply an even coat to the entire area you wish to color. You can create artistic effects such as drips and spatters by holding the spray nozzle closer to the metal than recommended, so the paint pools and streaks in places. Using this technique will increase the drying time, however. Once the entire piece is dry, you may add a second or third coat of paint to attain the desired color saturation.

If you plan on displaying your work outdoors, you may want to use a spray-on clear enamel coat to protect the piece against the elements. Once your primer and spray paint have been allowed enough time to dry fully, apply a thin layer of enamel or polyurethane and allow it to dry. Several coats will provide more protection, but allow ample time to dry fully in between coats.

If you only wish to color certain areas of your piece and you are not worried about durability and weatherproofing the piece, you can use latex or acrylic paint and brush-on primer to cover only the surfaces you need. Techniques such as sponge painting can be used to create distinictive patterns and textures as well.

Coloring with Oxidation

If you are working with steel, it is possible to add color through selective oxidizing of the material, giving a rust red appearance to the surface. Dissolve half of a cup of rock salt in a pint of water and put the solution in a plastic spray bottle. Spray the solution wherever you want rust to appear on the sculpture. Leave the solution on the sculpture for at least 48 hours. The oxidation will start out bright orange and gradually become darker over time. When the surface has developed the color you desire, you can stop the oxidation by sealing the surface with boiled linseed oil.

Steel can also be colored with gun bluing, available at most gun stores, that will make a layer of black or dark blue oxide on clean steel. Be sure to wipe down and sand the surface thoroughly to ensure an even coat. Gun bluing is corrosive and poisonous, so wear gloves, protective clothing and eye protection when working with it. You can either dip small pieces in the solution or paint it on to the surface of a piece with a paint brush. The solution should begin to oxidize the surface immediately, but to attain a darker shade, allow the solution to dry on the surface for an hour. Rinse the piece with water and apply a multi-purpose mechanic's oil to the surface to stop the reaction. If the black section appears dull or chalky, you can brighten it by buffing with a piece of fine steel wool, though this will also lighten the coloration. You may repeat the bluing process to attain darker shades as necessary.

Copper is capable of producing many interesting shades of oxide through the use of special patinas and techniques. Always clean and sand the surface of your copper before trying to oxidize the surface, so as to attain even coloring.

The simplest way to oxidize a piece of copper is to bury it in moist soil and leave it for up to a month The result will be a mix of green, blue, black and white oxides in organic, chaotic patterns.

A more controlled method would be to submerge the copper in a solution of distilled water, rock salt and ammonia and allow the copper to soak for several days to a week. This will produce a somewhat more uniform green coloration. More fast-acting results are possible using other chemical patinas.

Anodizing Aluminum

Anodizing is the process of coloring a piece of aluminum oxide by submerging it in sulphuric acid and passing current through the solution. This process is dangerous, as it involves corrosive acid and live current, so please take all safety precautions. Wear protective clothing, gloves and eye protection; always anodize in a well-ventilated area; and never touch live wires or liquid that live current may be going through.

As a safety precaution, mix a gallon of distilled water with two cups of washing soda and dissolve thoroughly. This solution will neutralize small concentrations of sulfuric acid. Dip any tools or containers that come in contact with acid in this solution to stop corrosion. If any acid comes in contact with skin, pour the washing soda solution over the area until completely neutralized.

Take an old 12-volt AC power adapter or battery charger and cut the end off of the wires (making sure that the adapter is not connected to live current). Strip both wires about 2 inches from the ends and label the positive and negative sides with tape.

Create the cathode by cutting a small piece of conductive sheet metal such as steel or copper and connecting it to the negative wire.

Clean the surface of the aluminum that you would like to color to ensure a good electrical connection. Now wrap the negative wire around the piece of aluminum, making sure that it is secure.

Dilute your sulfuric acid in a plastic bucket with distilled water at a ratio of six parts water to one part acid. Always add acid to water to prevent the acid from splashing out of its container. Clean all measuring equipment in the washing soda solution.

Place your cathode in the acid bath, followed by the piece of aluminum. Do not allow the cathode and aluminum to touch. They should be at least several inches apart. You may want to tape to wires to the sides of your bucket to prevent them from touching during the anodizing process. Once the wires are secure, plug the 12-volt AC adapter into an electrical outlet. The aluminum should start to bubble within several minutes. Leave the aluminum to anodize for an hour in a ventilated area.

Meanwhile, mix your fabric die with water in a separate plastic bucket and stir until dissolved.

Remove the 12-volt AC adapter from the electrical socket before touching either the cathode or the aluminum. Carefully remove the aluminum piece from the acid bath and rinse it in water. Place the piece in your plastic bucket of die and leave it for about 20 minutes.

Neutralize the left-over sulfuric solution by slowly adding baking soda to the mixture until it no longer fizzes. Carefully pour the neutral solution down a drain and rinse with water. Clean anything that comes in contact with the acid using the washing soda solution.

Remove your aluminum piece from the dye solution. It should be saturated with color at this point. Place the piece in boiling water for 20 to 30 minutes to seal the colored oxide. Remove from heat and allow to cool. The resulting colored oxide will be corrosion resistant and weatherproof.

Tips & Warnings

  • You can create artistic spatter effects using by spraying liquid spray paint into the plastic cap and then dripping paint directly onto primed metal surfaces.
  • Sulfuric acid is poisonous and highly corrosive. Wear gloves and goggles and handle with the utmost care.
  • Always add acid to water during dilution and always neutralize acid with baking soda before disposal.
  • Never touch exposed wires or conductive materials that are connected to electrical current. Electric shocks could result in injury or death.

References

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