I do several different patina colors on my bronze sculptures. I often get asked how they last. The bronze sculpture itself will last centuries, the patina on the bronze will age with time. Let me try to explain.
Indoors in a normal environment the patina will stay the same for decades. In humid environments, like a bathroom or pool area, they can change just like if they were outdoors. There are ways to prevent oxidation, and that is by waxing the sculpture with a clear paste wax. If you’re interested in waxing, I go into detail about waxing in another post. I have had several sculptures inside for over 20 years and no change has taken place, and no I haven't waxed them. However, if you live in a humid environment or the bronze is in direct sunlight, then I would recommend waxing at least once a year.
Outdoors environment is much more unstable, and waxing is required if you want to keep the patina color. The metal is living and will change with time. Just like we get older and wrinkly, the metal also changes. Many people like to see the changes in metal, others do not. If you don't then you need to wax regularly. Just like wrinkles, you can't go for years without taking care of the bronze and expect it to look like it did 5 years ago. And just like wrinkles, you can't wait until the bronze has begun to change, and then try to undo the aging process.
How will it change? An honest answer is I don't always know. It depends on the environment. Many conditions effect bronze oxidation and the time it happens. Moisture in the air, heavy pollution in the air, a water sprinkler constantly raining on the sculpture, direct sunlight, are just a few of the causes of bronze aging. Usually the bronze will deepen in color and start to turn a deep red, (wine or mahogany, not bright red) or possibly green. The oxidation process takes many years and some collectors covet the natural aging of the patina. The Statue of Liberty is a good example of the aging of a patina. It has developed a deep green verdigris. This verdigris layer protects and seals the bronze from further corrosion.
If you do not want the patina on the sculpture to change a consistent wax routine is required. The waxing of the sculpture needs to start after installing. In areas near the ocean or areas that have heavy pollution up to 4 times a year is recommended. After a rain the wax should bead up on the sculpture, just like it does on your car. If it doesn't it is time to wax. As I stated earlier, you cannot go 5 years without waxing and expect it to look the same as the day it was installed.
Natural patinas with clearcoat. The color is beautiful, like a gold ring. However, they will age. I do not do them for outdoor sculptures. I have done them for indoors. I put a coat of clearcoat on them. I let everyone know that I do not know how they change or how long it takes to change even indoors. The same factors affect the natural/with clear coat indoor sculptures as the outdoor sculptures. Several clients have bought sculptures with natural patinas, and I have not had any comments from them. But again, many clients embrace the natural aging of the patina.
In summary, the bronze sculpture will endure for centuries. The patina will age over time, even with strict maintenance. However, bronze is still the top choice for outdoor sculpture, because of the longevity of the metal. It has been proven to endure the test of time..