If you have a classic car that is plagued with decades of rust, you have a large task ahead to get the body of your car back to its former beauty. Unlike more modern vehicles, you can't just spray a rust inhibiting paint over the area and move on. You need to remove as much as possible and make what cannot be removed stable enough that it will not ruin all your restoration efforts. Here are some treatments to consider.
Media blasting is similar to sand blasting. It removes layers of rust and the old painted finish of your classic car. However, media blasting typically doesn't use sand because the rough particulates can damage the body and classic car parts. So, many auto body shops use materials that are actually designed to be tough on rust and paint, but gentle on the underlying body, leaving a smooth paintable finish. For example, one material is like engineered sand -- every particulate is rounded and they are all the same size. The rounded edges are not harsh, but their sheer volume and force removes just what needs to be removed. For less severe rusty cars, walnut shells can be used for blasting. If you're looking for the gentlest material used for media blasting, soda has also gained popularity.
If you're working with an auto body shop, you can have your car dipped in a chemical bath that dissolves rust, leaving clean steel behind. There are also DIY rust removal options. Some of them include a chemical paste that reacts with the rust. When you wipe the paste off, clean steel remains. This is more labor intensive, but can be less costly than professional treatments. If you're really worried about using chemical treatments on a delicate classic car, know that there are many methods that have been developed as environmentally friendly with low emissions; these are gentle on your car overall.
If the piece you are hoping to restore is not the exterior body, but a part of the engine or the underbody, you can restore the part easily by using a rust convertor instead of a rust stripper. Rust convertors contain tannic acid and an organic polymer that reacts with the rust (iron oxide). The iron oxide becomes iron tannate, and the polymer coats it, sealing the new material. The result is black, stable, and paintable surface that is protected from future rusting because the oxidization process has been stopped by the convertor.
Talk to professionals to learn more about rust inhibitor sprays.