Let me tell you a secret the luxury box makers hide: absolute hermetic sealing is often worse than open air. I've consulted for private collectors who dropped $20,000 on custom-built, gasket-sealed mahogany safes. They locked their pieces inside, felt incredibly secure, and opened the vault six months later to find devastating mold on organic porous materials and accelerated tarnishing on the metals.
The reality check here is moisture trapping. If you seal a box on a humid August afternoon in New York, you have just trapped that heavy, moisture-laden air inside a dark, stagnant micro-climate. When the room temperature drops at night, that trapped air reaches its dew point. Micro-condensation forms directly on the metal surfaces. Water acts as an electrolyte. Combine that with the natural sulfur off-gassing from the velvet glue or the wood itself, and you've essentially built a highly efficient corrosion chamber.
The trade-off is brutal. Open displays lead to rapid dust accumulation and gradual oxidation. Airtight safes require obsessive desiccant management. You cannot simply throw a silica packet in there and forget it. Silica gel is a sponge; once it is saturated, it stops working. If you don't bake it to recharge it, your "airtight" safe is useless.
I advise my clients to stop chasing the "perfect" seal. Instead, aim for buffered airflow. You want a container that drastically slows down air exchange without stopping it entirely, combined with reactive polymer linings that scavenge sulfur compounds dynamically. It feels counter-intuitive to leave a tiny gap in your preservation strategy, but allowing materials to breathe is fundamentally safer than risking micro-condensation. It requires slightly more frequent light maintenance, but it avoids the catastrophic structural degradation I routinely witness in bank deposit boxes.