Originally Posted by
baglamas
Aluminum forms spontaneously a non-reactive aluminum-oxide film on its surface that inhibits further corrosion. This is called passivation.
This protective film makes aluminum unsuitable as a sacrificial anode, but special aluminum alloys have been developed that do not passivate.
In other words your experiment did not work because you can't use regular aluminum as a sacrificial anode.
The reason that rust formed only on the side that was "up" is that more oxygen is available closer to the surface of the water.
Sacrifical anodes can only be used with an electrolyte (like the water in the experiment). So it's not possible to use this method of protection with objects like razors.
A more practical way to protect a blade made of carbon steel is to keep it clean, and coat it with oil before you store it (even cooking oil will do).
Even better solution: switch to stainless steel.