Sculptors have various prefered methods and suggestions for preserving and caring for sculptural art work. My suggestions are based on striking balance between ease of use for the collector and acheiving at least equivalent visual and protective quality to other more intensive routines. The end goal is low maintanance to preserve the "Gallery Fresh Look" for lifetimes to come.
Please do note that "rust never sleeps". Expect an ever chainging surface appearance.
Outdoor Sculpture (Natural Rust Patina)
ZAR exterior water based poly in a clear satin finish can be applied with a brush. I apply a first coat with a sprayer so that the rust patina does not smear. Re-coats are usually required about once a year. It is not necessary to sand "rust break through" spots. The finish will seep into the rust to create a desired coating.
This product unfortunately is not easily found. You can check online for a local specialty paint store that caries the line. If you are having difficulty finding it let me know. I usually have some in stock that I can sell you.
Indoor Frequent Care
Johnson's Paste Wax is commonly found in grocery and hardware stores in the furniture care section. I recommend this product for my indoor pieces which have a brushed steel (shiny) finish. This is especially easy to use if the piece has wood components since it works great for steel and wood. Primary care should be a feather duster only. Secondary care (approximately once a year) would be to wipe the piece with a barely damp cloth and a dab of mild household cleaner. Avoid products with bleach or vinegar. These are acidic and will promote rust which in this case you are trying to avoid. After the piece is thoroughly dry you can wipe on the paste wax and then buff off lightly.
Indoor Extreme Re-finish
In the case that your shiny brushed steel sculpture or furniture has been exposed to salt air or high traffic, you may be noticing rust
In the case that you don't mind or even like the new coloration, just refer to the frequent indoor care link (paste wax). If, however, you are wanting to restore the piece to the shiny finish, then you will have a complex process that you may want a professional to tackle. You need a workshop type environment, an angle grinder with a wire-brush attachment, safety goggles. A respirator is recommended.
First, wire-brush the piece back to its shiny state. Next clean it with lacquer thinner (heavy chemical gloves are a must!). After cleaning be sure not to touch the piece with bare hands. Body oils will break right back through the new finish. Now you are ready to apply the clear coat. The Krylon Crystal Clear spray can is found at most hardware stores and K-Mart. Done.
To prevent the need for this drastic make over in the future, take the "frequent care" steps a bit more often.