The floor corkers actually use brass irises in most cases unless they are plastic(which wouldn't rust). This is actually oxydation on the brass. It is tricky but the best semi-permanent fix would be to disassemble the iris and clean the parts of the oxydation. This could be a hazard so caution should be observed as noted by Smurfe.After the surfaces are cleanapply several thin coats of a spray laquer(no not liquor) to prevent further oxydation. Reassemble when dry and you should be all set without fear of food contaminatin from oils.
Here is an article that covers such related rusting-oxydation.
Unstable Metals
Many metals are very unstable. Think of it. You just don't go up to upper Minnesota and find steel I beams growing out of the ground. A trip to the hills of Jamaica will not uncover aluminum cans or aluminum siding sprouting from the hillsides. On the contrary - aluminum, steel, copper, zinc and other metals look much different in their natural state. The metal ions are often coupled with other elements. Iron, for example, is often coupled with oxygen. The mineral hematite is simply 2 atoms of iron and 3 atoms of oxygen - Fe2O3. The iron is very happy in this state. Heck, it probably was like that for millions of years!
When we refine metals we change all that. We throw the iron ore into a blast furnace and strip away the oxygen atoms. We produce raw steel. The steel is very unhappy and wants to get back to its original state. It will readily do this in the presence of water. The result is rust! Rust is simply stable iron - Fe2O3
Brass is no different. Brass is simply an alloy of copper and zinc. Both copper and zinc are unstable in their refined states. Combined they are still unstable. The tarnish that develops on brass is basically "rust". Tarnish and rust are actually protective coatings. When this film forms on the surface further oxidation or "rusting" is slowed down. The tarnish or rust hides the remaining pure metal from the outside elements. That is why each time we polish steel, brass, or sterling silver, it begins to tarnish again. The tarnish wants to protect the remaining pure metal.
The Tool Industry
Nearly 25 years ago the tool industry developed a way to coat metals with stable metals. The coating helped improve performance and extend tool life. An ultra-thin layer of gold was applied to titanium nitride drill bits.
About five years ago the light bulb went off in someone's head. They decided to try the same thing with brass. An alloy of nickel was used. Working in a vacuum, they applied an ultra-thin layer - forty millionths of an inch thick! - to the brass. Then a hardener was applied. Zirconium was added in the presence of nitrogen. The result was a metallic protective layer on the polished brass. The most interesting thing was that the layers of the metals were so thin, you could see through them! Tarnish free brass was here. It will soon be available in just about any form. Regular brass hardware and plumbing fixtures are readily available. Just about any brass piece will probably be able to be purchased with a lifetime tarnish-free guarantee.
In fact, I'll bet that within 10 years you will be able to take old brass objects like my porch lights and have them cleaned and coated with the magic metal films. It is just a matter of time before a company offers this service. The technology is here. All you will have to do is arrange the back and forth shipment!
Regular Restoration
For now I'm stuck with restoring my brass fixtures. Outdoor brass suffers and tarnishes more readily than indoor brass. The reason is simple. Moisture accelerates the chemical reaction that results in tarnish. Couple that with the destructive forces of ultraviolet (UV) rays from sunlight and you have a real problem.
UV rays can erode and blast apart the resins that make up clear lacquer coatings on decorative brass. The naked eye can't see this happening. However, it happens the instant you hang those fixtures or brass house numbers. What's worse is that you do not know the quality of the lacquer that was used at the brass factory. Perhaps a cheap lacquer was used. Perhaps only two coats were applied. All this in an effort to save money.
If you want to minimize restoration work on your existing or new brass, then you must coat the brass with 3 to 5 coats of clear lacquer before you place it outside. Spray lacquers are easy to apply and dry rapidly. Experiment on a scrap piece of metal before spraying the real piece.
Exterior brass needs to be recoated each year to prevent tarnish. Don't let your brass get away from you like mine did!
I'll go drink some wine and wait for an answer.
