A piece of hammered copper with a muratic acid patina is contrasted with a sheet of decorative copper that has not been treated.
Normally I would put the legal disclaimers at the end of an article, but the title of this piece warrants an upfront notice that simple and safe are two relative terms. While simple can be argued from an age or ability standpoint, “safe” is the term that is more of a concern to me. When statements are made that involve the term “safe” people can have a false sense of security. Even mild acids can be painful and harmful in the eyes, and when dealing with sprays there is always the potential for misted liquids to become airborne and land where they were not intended. When using a spray bottle to apply liquids on copper consider the wind direction and always hold the material downwind. Also, before you begin any application you should know what the neutralizer is for any acid you intend to use and have it handy just in case it is needed quickly. Even mild acids can be quite painful. You will want to see the results of your efforts, so always wear safety goggles to protect your eyes and rubber gloves to protect your hands. It is also a good idea to wear old clothes that you won’t mind spoiling.
Now that you’ve got your copper prepared it’s time to say that creating copper patinas is more of an art than a science. Results will vary, sometimes dramatically, so proceed with an open mind.
The first step to any patina project is preparing the metal, and cleaning off the residue of milling, handling and environmental collectives can be handled with a simple washing of dish soap and hot water may be adequate. For more fouled surfaces cleaners that contain trisodium phosphate are more effective, but also more offensive to skin. Avoid cleaners which leave a coat of oxide on the copper surface. You’ll know if the cleaning process has been done properly if you wash the copper off after cleaning and the water sheets uniformly and does not form beads. Beading indicates the presence of oils or contaminates and additional cleaning will be required.
Salt, or sodium chloride, when combined with acetic acid from the vinegar produces sodium acetate and hydrogen chloride. Hydrogen chloride is a strong acid and the combination of it and sodium acetate will quickly clean a copper surface. This cleaning process will give your metal a very pure surface, which will corrode quickly when exposed to water and the combination of oxygen and carbon dioxide in the air.
Small pieces of copper can be sprayed with vinegar, sprinkled with salt and put in a sealed plastic or glass container with a dish of cloudy ammonia overnight. The following day, rinse the mixture off and let it dry. The results should be a blue patina on a dark background. You can also embed pieces of copper in sawdust that has been dampened with vinegar. This gives an interesting effect but less colorful.
Another option for a green patina is to mix 1 Tbsp ammonium chloride (Sal ammoniac) with 1 Tbsp salt and 1 ounce of ammonia in a spray bottle with 1 quart of bottled or distilled water. Warm or hot water will help dissolve the dry ingredients more quickly. Spray it on a clean copper surface and let stand for three hours for a nice green color. Repeat several times for increased coloration. Sal ammoniac is not something that you’d normally have in your everyday kitchen, but in the spirit of “safe” chemicals I’m throwing this one in the mix. Although the kitchen aspect of this chemical is rapidly dying due to the general disuse of it as an ingredient, in the past, sal ammoniac has been used by bakers to give cookies a crisp texture. If you don’t use it in your favorite cookie recipe, it is available online from a number of sources.
Another blue-green patina can be achieved by placing a piece of copper in a glass or plastic container and covering it with sawdust saturated with ammonia liberally mixed with salt. In an hour or so you’ll begin to see a nice speckled blue-green surface. Varying the mixture and the density of the sawdust will alter the results, perhaps more to your liking.
Muriatic acid will also produce a pretty blue-green color if diluted, then sprayed on and left over night. You can pick up muriatic acid at your local hardware store. Just remember that muriatic is actually a 20% solution of hydrochloric acid so be very careful that you have adequate ventilation and the safety precautions I covered earlier.
Other colors can be obtained with preparations such as gun bluing chemicals which can produce either a blue or brown effect. Another option for brown coloration would be uric acid, which has used to apply patinas on copper and its alloys brass and brass. The most common source is cow urine. The break-down or the ammonia cycle seals and purifies the rich, brown coloration.
I’m sure there are other chemicals and combinations of chemicals that you will want to try, once you become bitten by the patina bug. These are but a few that are simple, relatively safe, and most readily available for experimentation. The most important part of the process is to do it. Get some copper, create something, and add a patina to the finish. It’s fun, it’s creative, and it’s copper!
Important note
In my experience of doing the chemical treatments on copper like the writer said, make sure you have adequate ventilation and if you choose to lighten your work it is best if the item is wet when you do it. When done dry the powder will get in your system and can cause health issues later.
Greg Nielsen
Copper Tech Construction, Inc.
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