Why does bronze tarnish and rust?

A Bronze alloys contain copper. When bronze oxidizes (comes in contact with water and oxygen) or “rusts”, the process causes the bronze to turn in a green color. You may recall the Statue of Liberty is green – due to oxidation.

If you have ever been to historical parks such as Monument Avenue, in Richmond VA, Washington DC, Gettysburg PA, or NYC’s avenues of art, you’ll see that the bronze sculptures, of famous American soldiers, mascots, and even some fountains, are green. Other monuments are rich brownish bronze. The difference between the two finishes is whether the park has decided to preserve the bronze with wax, or let it go natural (“verdigris”).

Once oxidized, this verdigris crystalline layer (called a “passivation layer”) actually protects, and seals the metal from additional corrosion. Hence, the Statue of Liberty stays green.

What is patina?

Today’s bronze art objects come from the foundry with a chemical patina (green film). This protective layer changes the outside metal structure to prevent corrosion. Foundries may also add wax, lacquer, or urethane coatings to protect the valued warm bronze color.

How can I let my bronze naturally turn verdigris?

Placing your mascot or statue outdoors will naturally cause it to turn green, verd or verdigris (green patina). Many people find this antique patina of green desirable, and may want to quickly customize their bronze using a tinted finish. Today, many foundries actually acid-etch the metal, to give the effect of antique verdigris.

How long does it take for bronze to get verd?

In direct sun, un-maintained and exposed to the weatherï¿½.more than of 5-10 years and slightly shorter on the beach with salt water spray.

How can I keep my bronze the same original color?

Simply paste wax your monument every year or coat it with clear Permalac ™, urethane, or lacquer spray.

What about white spots?

When you first get your bronze, borax powder – used in casting – can look like crystals. The borax may be still in the metal, but not visible until it gets wet. If you see these crystals, simply wash them off, or clean with paste wax.

You may also see some white spots due to residual ceramic material from casting as well. Again, simply clean it up with paste wax, and touch up the color with Kiwi wax.

After bringing your bronze home, high calcium levels in the water often cause white spots, especially in fountains. This happens often in locations with heavy mineral content. Remove the spots using a good paste wax, and use de-mineralizing chemicals to treat the water. (Note: De-mineralizing agents can be found in most pool supply stores.)

What kind of paste wax is recommended for bronze?

Do not use automobile paste-waxes, as these will permanently damage bronze. Johnson\ï¿½s, Boston, or any non-abrasive, natural paste waxes are recommended.

For quick and shiny cleanups, use a spray-after-wash auto detailer that contains only wax.

Can I use tinted paste wax?

Some foundries use Kiwi shoe paste, which comes in brown, black, cordovan, and oxblood, to create a reddish-brown tint and add depth. This can be done at home. However, itï¿½s not advisable to use it where a heavy coat of wax has already been applied by the foundry.

How long does bronze last?

Almost forever! Archeologists are still discovering Greek and Roman bronze from the Mediterranean Sea, dating thousands of years ago. Interestingly, the very word verdigris comes from the word “verde” (Old French: green) and “verde gris” (Latin: of Greece). These artifacts are still in good and identifiable condition.

How can I repair damage or scratches to my bronze?

For minor touch ups to your bronze art, refinishing kits, metal chemical patinas, and color-solvent dyes are available on the Internet (search under “bronze refinishing kits”).

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