Those of you who remember my witterings from before Christmas will know that I was running a little experiment to see whether a spray sold to prevent photographic developer from oxidising would prevent steel from rusting. I cut two short lengths of steel bar, dunked each into sea water for half its length, allowed to dry and then sealed them in plastic tubs for a couple of weeks, one filled with air and the other with Tetenal Protectan spray. Results: two pieces of steel with surface rust over half their lengths. Looking very closely, it is possible to make out a difference - the rust spots on the "protected" steel are rather smaller and more even than those on the unprotected steel, so the spray does have some effect. However, as a rust preventative it has clearly failed.
In theory, the spray should have expelled all the oxygen from around the steel, preventing it from oxidising. It obviously didn't. It's possible that only a very small amount of oxygen remained and that had I run the experiment for longer, the "protected" steel would not have continued to rust any further, but I see little point persevering.