A couple weeks ago I bought a National Magic Lindhorst style vanishing cage off of the Martinka auction. (Very professional auction - BTW).
I wanted the National Magic brand of cage for its construction characteristics and to modify for an experiment. This was quicker and easier than making a new cage to modify. When the cage arrived, I immediately noticed that it had not been properly taken care of by the previous owner(s). The aluminum cage frame had been allowed to become extremely pitted due to contact with perspiration from the performer. I bought an old Owen cage with the same problem about 25 years ago. If left unchecked, the aluminum will completely disappear. Now, that's a real vanishing cage!
Fortunately, I am in a position where I can refurbish such a cage and this corrosion, if caught early enough, really is not an insurmountable problem. I was able to completely clean up the cage and remove virtually all traces of this mistreatment with only one broken brass bar. I'll replace that later. Cleaning up such a cage is not a fun project.
The purpose of this posting to to alert magicians to this problem and provide a suggestion which will help to prevent your expensive cages from being eaten away and prematurely vanishing.
If the performer will (now and then) either wax or polish the cage with something like Flitz, this potential problem can be avoided. Cages are tedious to make and hence costly. Do yourselves a favor and "baby" those cages. They will serve you well for years with the proper care.