Articles - Sculpt Nouveau

How Do You Dispose of Your Patina Chemicals? - Bury Them!

Ancient Buried Process by Ron Young

Environmentalists, OSHA, take heed. My favorite means of dealing with old or unwanted patinas is to recycle them using a buried process. Any patina solution may be used and this process is practical for any individual sculptor or small foundry. This process can create rich colors and beautiful textures on copper, brass and bronze. The buried patina mixture will last for years and it may even get better with time.

The buried patina process consists of placing a bronze object into a container filled with a granular material such as sawdust, dirt, or cat litter. This material is then moistened with the patina solution. The contact of the moistened material with the metal object created a variegated surface. The exact finish and color will depend three factors. The first is the texture of the material. The second is the strength and type of the patina solution and the third consideration is the amount of time the object is left in the container.

Fine sawdust will produce a densely textured patina, while a coarse substance such as wood shavings or wood chips will result in a textured surface. The best type of sawdust to use is white pine or Douglas fir. Hardwoods will not absorb the patina, while redwoods contain tannic acids which turn everything black. Soil or dirt is another possibility. Soil will add a degree of unpredictability because it contains various minerals. Cat litter works well too. Begin with a clean, fresh material to avoid unwanted contaminants. After the container has been established, it will not need to be changed. If the material dries out, it may be reactivated by adding water. Choose an airtight container to work in that will not react with the patinas. I use 5 gallon plastic pails or for larger pieces, plastic trash cans. Plastic garbage bags may also be used.

The bronze, brass, or copper object should be sandblasted before being placed in the buried container. Sandblasting cleans the metal, allowing the patina to react, and gives the surface a slight tooth or texture. A hot patina may be applied after sandblasting. This will give a controlled base patina color. Another option is to polish the surface of the metal then place aluminum foil over it. The fumes formed under the aluminum foil will create beautiful rainbow colors on the metal. These techniques may be combined by masking off areas with tape, wax, or a good lacquer.

Wear gloves and safety glasses when working with patina solutions. Pour the saved patina into the sawdust or other material. Mix in the patina solution. Leaving the sawdust too dry will limit the patina to random areas. Over saturated material will allow the patina to settle in pools on the metal and eventually will flake off after drying. A dependable guide is to take a handful of the sawdust and squeeze it; no patina should run out of the sawdust yet it should be visibly damp. Pack the patina mix around the object. The harder the material is pressed around the metal the more dense the patina will be. Next close the container which will hold in the patina fumes and prevent the material from drying out. I have multiple containers at my studio available to hold old patinas. The patina solutions become more predictable as you group certain solutions together.

For the blue/green patinas add all of your old copper carbonate, copper sulfate, copper chloride, copper nitrate, and cobalt nitrate. Household ammonia and vinegar may be added for extra color.

For white/gray patinas have a container for old bismuth nitrate, silver nitrate, and stannic oxide.

For black patinas add any liver of sulfur, ammonium sulfide, or Birchwood Casey's brown or black. To make a dark green out of the black add household ammonia and vinegar to the mixture.

For oranges, gold and browns add any potassium dichromate, ferric nitrate, or ferric vinegar to the mixture.

The patina process will take from one to six days. Check the piece each day to monitor the progress. Remove the object when the patina has reached the point you like. Carefully brush off the loose material. The patina is very fragile at this stage, especially if still wet. Let it air dry before handling it too much. Material will probably be permanently stuck to the surface if the container has been allowed to dry out during the process. If the material you have used is wood, this usually causes crystals to form giving the resulting patina the interesting appearance of antiquity. Another method is to place the metal object on top of the material and allow the fumes alone to create a patina. The true patina color will not be seen for at least a day after removing the object from the container.

Rinsing the object after it has been patinated is an option. Rinsing with cold water may change the patina slightly. Rinsing with hot water will definitely alter the patina. Spraying on acetone will neutralize the chemicals, keeping the colors as they are. Let the object dry for at least a day then spray with a matte varnish. The matte varnish will only set the color, not change it. The piece may be left as is at this stage. An additional layer of wax or lacquer may also be applied; either of these will cause the patina to darken. The patina will become stronger with time.

This ancient patina technique is a timely addition to anyone's collection. The patinas are interesting and beautiful, yet beneficial to the environment. Although, you may find buried patinas so engaging, as I do, that you begin making new patina solutions to just to fill the buried containers. Please, check with your local government agency for further chemical disposal suggestions.

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