Different Effective Approaches To Cleaning Bronze
The desired goal in cleaning bronze can be different than that for cleaning some other materials. You may want to restore a bronze (or brass) item to its original shiny finish, or you may want to retain the patina that has accumulated, and only clean, but not polish, your bronze piece.
When you are cleaning bronze, you are cleaning mostly copper. Bronze is a copper alloy, and most bronze pieces you are apt to encounter will be an alloy of 88% copper and 12% tin. Other alloying elements are at times used instead of tin, the main ones being phosphorous, selenium, and aluminum, each alloy being used for a specific set of purposes. If you have an alloy of 90% copper and 10% zinc, you have brass. The methods used in cleaning brass are for all practical purposes the same as those used in cleaning bronze.
There are many commercial metal cleaners on the market, some of which specifically address bronze (usually bronze, brass, and copper). Depending upon the bronze item or items you wish to clean, you may choose one of the commercial cleaners, or you may avoid them completely. In some cases, commercial cleaners will do more harm than good. Believe it or not, the bronze cleaning methods preferred by most people who own or trade in bronze items, use what could be best described as home remedies.
How To Clean A Grizzly (Statue) - A case in point. There is a small town near where I live that is somewhat of an artist's colony, and has several world-class sculptors among its inhabitants. One day I happened to be watching one such person carefully cleaning a life-sized bronze grizzly bear. He was working on this very large bear with a toothbrush in hand. I was a little hesitant to ask him how one goes about cleaning a large outdoor bronze statue, figuring that the method he was using was some deep, dark, and perhaps patented secret. Here is how goes about cleaning a large statue of a grizzly bear, a moose, a horse, or Julius Caesar.
The Cleaning Job - The goal was to remove the patina, oxidation which causes bronze to turn green, and at the same time apply a protective agent that would keep the patina from returning, at least for several months. To start with, the statue is cleaned with good old soap and water. Not enough soap to make suds, as that may leave a soapy film that would have to be rinsed off later. The first step in the process then was applying soap and water, with plenty of elbow grease, to get everything clean. The toothbrush was used to get into the smallest nooks and crannies, where of course dirt often accumulates. Once the cleaning had been accomplished, the entire statue was wiped dry with a beach towel, plus a few smaller towels (for the ears?).
The Wax Job - When dry, the final step was to apply a protective layer of wax to the surface. This was done with a small paintbrush, again to get at the nooks and crannies, although a soft rag also could have been used in most places. The wax could be heated, or the statue could be waxed on a hot day. The wax? Johnson's Paste Wax! My sculptor acquaintance said that this common commercial paste wax was what he used on almost every outside statue, and most of his colleagues used the same. About the only departure from Johnson's, was the use of Trewax for lighter colored pieces (this particular bear was very dark in color). Once the wax was dry it was a simple matter to buff the statue to a nice shine. And that was it!
One cautionary note was not to use automobile wax as that could give a negative effect, as could some commercial metal polishers. The process mentioned could be taken one step further by applying Armor All, which is a liquid silicon, and a safe way to provide an extra layer of protection.
Another wax product is Renaissance Wax, which is favored by many museum curators. Special care needs to be taken when cleaning antique bronze items. Removing the patina could in these cases be quite undesirable. An antique bronze piece, especially one you would find in an antique dealers shop, would lose its value quickly if the patina were rubbed off, and replaced with a brilliant shine. The antique would take on the look of a cheap reproduction.
Two Alternative Cleaning Solutions - If you have some antique bronze coins, or bronze family heirlooms, you probably desire to keep them old looking, that is, retain the patina, but still be clean. Besides soap and water, you can use a baking soda/lemon juice paste. Rub the pate into the item, let it sit for a few minutes or longer, and then rinse and dry. A flour-vinegar-salt paste is also claimed to do an excellent job of cleaning bronze, again without removing the patina.
When you stop to think about it, as far as cleaning bronze is concerned it's a pretty straightforward process, and you don't have to pay $19.95 (plus shipping and handling, but you get a second bottle free) for the latest and greatest commercial bronze cleaner. Just head for your pantry.