Posted By:
Gilbert MainesAtmospheres go through great pains, it seems in their desire to become uniform. The constitiuents migrate until everything is equal throughout the entire containment. This applys to moisture as well as pollutants and other atmospheric components.
Silica Gel has an affinity for moisture, hydrocarbons, and other compounds potentially harmful to cards. As such, it draws these things out of the atmosphere and retains them in its crystaline lattice.
Sooner of later the Silica Gel becomes ineffective, because it has adsorbed all that it can. At that time you can choose to replace it, regenerate it, or ignore it.
Since the Silica Gel impacts the entire atmosphere inside of the safe, placement of this dessicant is unimportant to the well being of your cards. The atmosphere inside of your safe includes that "space" inside of your slabs and screwdowns, since neither are air tight (if they were this post would be unnecessary).
Edited to try to spell bettah
Of course, the closer the silica gel is positioned in relation to your cards the more quickly it will impact them, however, eventually the entire internal atmosphere of the safe will be equal.
How often you open the safe has a significant impact on the dessicant's ability to do this job.